ZJ COOLING SYSTEM 7-1 COOLING SYSTEM CONTENTS page pageDIAGNOSIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 SERVICE PROCEDURES . . . . . . . . . . . . . . . . . . 11ENGINE ACCESSORY DRIVE BELTS . . . . . . . . . 40 SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . 50ENGINE BLOCK HEATER . . . . . . . . . . . . . . . . . . 48GENERAL INFORMATION matic transmission fluid (if equipped). The cooling Throughout this group, references are made to par- system is pressurized and uses a centrifugal waterticular vehicle models by alphabetical designation or pump to circulate coolant throughout the system.by the particular vehicle nameplate. A chart showing An optional factory installed maximum duty cool-a breakdown of alphabetical designations is included ing package is available on most models. This pack-in the Introduction section at the beginning of this age will provide additional cooling capacity formanual. vehicles used under extreme conditions such as trailer towing in high ambient temperatures.COOLING SYSTEM The cooling system regulates engine operating tem- COOLING SYSTEM COMPONENTSperature. It allows the engine to reach normal oper- The cooling system consists of:ating temperature as quickly as possible. It also • A radiatormaintains normal operating temperature and pre- • Cooling fanvents overheating. • Thermal viscous fan drive The cooling system also provides a means of heat- • Fan shrouding the passenger compartment and cooling the auto- • Radiator pressure cap Fig. 2 Engine Cooling System—5.2L Engine—Typical
7-2 COOLING SYSTEM ZJ• Thermostat• Coolant reserve/overflow system• Transmission oil cooler (if equipped with an auto-matic transmission)• Coolant• Water pump• Hoses and hose clampsSYSTEM COOLANT ROUTING For cooling system routings refer to (Figs. 1 or 2). Fig. 1 Engine Cooling System—4.0L Engine— Typical
ZJ COOLING SYSTEM DIAGNOSIS 7-3 DIAGNOSIS INDEX page pageDRB Scan Tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Preliminary Checks . . . . . . . . . . . . . . . . . . . . . . . . . 4On-Board Diagnostics (OBD) . . . . . . . . . . . . . . . . . . 3ON-BOARD DIAGNOSTICS (OBD) It is possible that a DTC for a monitored circuit may not be entered into memory even though a mal-FOR CERTAIN COOLING SYSTEM function has occurred. Refer to On-Board DiagnosticsCOMPONENTS (OBD) in Group 14, Fuel Systems for additional in- The powertrain control module (PCM) has been formation.programmed to monitor certain cooling system com- ACCESSING DIAGNOSTIC TROUBLE CODESponents: A stored Diagnostic Trouble Code (DTC) can be dis-• If the engine has remained cool for too long a pe- played by cycling the ignition key On-Off-On-Off-Onriod, such as with a stuck open thermostat, a Diag- within three seconds and observing the malfunctionnostic Trouble Code (DTC) number 17 can be indicator lamp. This lamp is displayed on the instru-observed at the malfunction indicator lamp. This ment panel as the CHECK ENGINE lamp (Fig. 3).lamp is displayed on the instrument panel as the They can also be displayed through the use of theCHECK ENGINE lamp (Fig. 3). Diagnostic Readout Box (DRB) scan tool. The DRB connects to the data link connector in the engine compartment (Fig. 4). For operation of the DRB, refer to the appropriate Powertrain Diagnostic Procedures service manual. Fig. 3 Check Engine Lamp Location If the problem is sensed in a monitored circuit of-ten enough to indicate an actual problem, a DTC isstored. The DTC will be stored in the PCM memoryfor eventual display to the service technician. If theproblem is repaired or ceases to exist, the PCM can-cels the DTC after 51 engine starts. Certain criteria must be met for a DTC to be en-tered into PCM memory. The criteria may be a spe-cific range of engine rpm, engine temperature and/or Fig. 4 Data Link Connector Location—Typicalinput voltage to the PCM. EXAMPLES: A DTC indicates that the PCM has recognized an • If the lamp (Fig. 3) flashes 1 time, pauses andabnormal signal in a circuit or the system. A DTC flashes 2 more times, a flashing Diagnostic Troublemay indicate the result of a failure, but never iden- Code (DTC) number 12 is indicated. If this code istify the failed component directly. observed, it is indicating that the battery has been disconnected within the last 50 key-on cycles. It
7-4 COOLING SYSTEM DIAGNOSIS ZJcould also indicate that battery voltage has been dis- • Increasing engine speed for more air flow is recom-connected to the PCM. In either case, other DTC’s mended.may have been erased. 2. TRAILER TOWING:• If the lamp flashes 1 time, pauses and flashes 7 Consult Trailer Towing section of owners manual.more times, a flashing Diagnostic Trouble Code Do not exceed limits.(DTC) number 17 is indicated. 3. AIR CONDITIONING; ADD-ON OR AFTER After any stored DTC information has been ob- MARKET:served, the display will end with a flashing DTC A maximum cooling package should have been or-number 55. This will indicate the end of all stored in- dered with vehicle if add-on or after market A/C isformation. installed. If not, maximum cooling system compo- nents should be installed for model involved perERASING TROUBLE CODES After the problem has been repaired, use the DRB manufacturer’s specifications.scan tool to erase a DTC. Refer to the appropriate 4. RECENT SERVICE OR ACCIDENT REPAIR:Powertrain Diagnostic Procedures service manual for Determine if any recent service has been performedoperation of the DRB scan tool. on vehicle that may effect cooling system. This may be:DRB SCAN TOOL • Engine adjustments (incorrect timing) For operation of the DRB scan tool, refer to the ap- • Slipping engine accessory drive belt(s)propriate Powertrain Diagnostic Procedures service • Brakes (possibly dragging)manual. • Changed parts (incorrect water pump rotating in wrong direction)PRELIMINARY CHECKS • Reconditioned radiator or cooling system refilling (possibly under-filled or air trapped in system).ENGINE COOLING SYSTEM OVERHEATING • Rubber and foam air seals not properly installed to Establish what driving conditions caused the com- radiator or A/C condenser after a repair.plaint. Abnormal loads on the cooling system such as • Upper and lower portions of radiator fan shroudthe following may be the cause. not tightly connected. All air must flow through the 1. PROLONGED IDLE, VERY HIGH AMBIENT radiator.TEMPERATURE, SLIGHT TAIL WIND AT IDLE, If investigation reveals none of the previousSLOW TRAFFIC, TRAFFIC JAMS, HIGH items as a cause for an engine overheating com-SPEED, OR STEEP GRADES: plaint, refer to following Cooling System Diag- Driving techniques that avoid overheating are: nosis charts.• Idle with A/C off when temperature gauge is at These charts are to be used as a quick-referenceend of normal range. only. Refer to the group text for information.
ZJ COOLING SYSTEM DIAGNOSIS 7-5 COOLING SYSTEM DIAGNOSIS
7-6 COOLING SYSTEM DIAGNOSIS ZJ COOLING SYSTEM DIAGNOSIS (CONT.)
ZJ COOLING SYSTEM DIAGNOSIS 7-7 COOLING SYSTEM DIAGNOSIS (CONT.)
7-8 COOLING SYSTEM DIAGNOSIS ZJ COOLING SYSTEM DIAGNOSIS (CONT.)
ZJ COOLING SYSTEM DIAGNOSIS 7-9 COOLING SYSTEM DIAGNOSIS (CONT.)
7 - 10 COOLING SYSTEM DIAGNOSIS ZJ COOLING SYSTEM DIAGNOSIS (CONT.)
ZJ COOLING SYSTEM SERVICE PROCEDURES 7 - 11 SERVICE PROCEDURES INDEX page pageAutomatic Transmission Oil Coolers . . . . . . . . . . . . 38 Refilling Cooling System . . . . . . . . . . . . . . . . . . . . 26Coolant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Testing Cooling System for Leaks . . . . . . . . . . . . . 26Coolant Reserve/Overflow System . . . . . . . . . . . . . 28 Thermostat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20Cooling System Cleaning/Reverse Flushing . . . . . . 26 Viscous Fan Drive—All Engines . . . . . . . . . . . . . . 36Cooling System Fan . . . . . . . . . . . . . . . . . . . . . . . 35 Water Pump Bypass Hose—5.2L V-8 Engine . . . . . 18Cooling System Hoses . . . . . . . . . . . . . . . . . . . . . 34 Water Pump Tests . . . . . . . . . . . . . . . . . . . . . . . . . 11Draining Cooling System . . . . . . . . . . . . . . . . . . . . 25 Water Pumps—General Information . . . . . . . . . . . . 11Radiator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Water Pumps—Removal/Installation . . . . . . . . . . . 12Radiator Pressure Cap . . . . . . . . . . . . . . . . . . . . . 28WATER PUMPS—GENERAL INFORMATION A centrifugal water pump circulates coolantthrough the water jackets, passages, intake manifold,radiator core, cooling system hoses and heater core.The pump is driven from the engine crankshaft by asingle serpentine drive belt on all engines. The water pump impeller is pressed onto the rearof a shaft that rotates in bearings pressed into thehousing. The housing has two small holes to allowseepage to escape. The water pump seals are lubri-cated by the antifreeze in the coolant mixture. No ad-ditional lubrication is necessary.CAUTION: All 4.0L 6-cylinder engines are equippedwith a reverse (counterclockwise) rotating waterpump and thermal viscous fan drive assembly. RE-VERSE is stamped or imprinted on the cover of theviscous fan drive and inner side of the fan. The let-ter R is stamped into the back of the water pumpimpeller (Fig. 1). Engines from previous modelyears, depending upon application, may have beenequipped with a forward (clockwise) rotating water Fig. 1 Reverse Rotating Water Pump—4.0Lpump. Installation of the wrong water pump or vis- 6-Cylindercous fan drive will cause engine over heating. DRAINCOCK WITH THE SYSTEM HOT AND UNDER PRESSURE. SERIOUS BURNS FROM THE COOL- A quick test to determine if the pump is working isto check if the heater warms properly. A defective wa- ANT CAN OCCUR.ter pump will not be able to circulate heated coolant (1) Drain the cooling system. Refer to Drainingthrough the long heater hose to the heater core. Cooling System in this group. 5.2L ENGINE: One of the heater hoses is con- (2) Loosen the fan belt. Refer to Belt Service in thenected to the water pump with a metal coolant re-turn tube (Fig. 2). A rubber o-ring forms a seal at the Engine Accessory Drive Belt section of this group.water pump end of the tube. (3) Disconnect the lower radiator hose from the water pump.WATER PUMP TESTS (4) Bend a stiff welding rod or similar device as shown in (Fig. 3). To prevent breakage of rod, mini-LOOSE IMPELLER mum thickness should be 3/16 inch (.187 inches). DO NOT WASTE reusable coolant. If solution is (5) Position the rod in the water pump inlet andclean, drain coolant into a clean container for reuse. attempt to hold the impeller while turning the fan pulley. If equipped with a thermal viscous fan drive,WARNING: DO NOT REMOVE THE CYLINDER rotate the water pump shaft with a wrench attachedBLOCK DRAIN PLUGS OR LOOSEN THE RADIATOR to one of the fan pulley mounting nuts. If the impel-
7 - 12 COOLING SYSTEM SERVICE PROCEDURES ZJ DO NOT WASTE reusable coolant. If solution is clean, drain the coolant into a clean container for re- use. WARNING: DO NOT LOOSEN THE RADIATOR DRAINCOCK WITH THE SYSTEM HOT AND UNDER PRESSURE. SERIOUS BURNS FROM THE COOL- ANT CAN OCCUR. (1) Drain sufficient coolant from the radiator to de- crease the level below the water pump heater hose inlet. (2) Remove the heater hose. (3) Inspect the inlet for metal casting flash or other restrictions. Remove the pump from the engine before re- moving restriction to prevent contamination of the coolant with debris. Refer to Water Pump Removal in this group. WATER PUMPS—REMOVAL/INSTALLATION Fig. 2 Coolant Return Tube—5.2L V-8 Engine REMOVAL—4.0L 6-CYL. ENGINEler is loose and can be held with the rod while the The water pump on all models can be removedfan blades are turning, the pump is defective. Do not without discharging the air conditioning system (ifuse excessive force when rotating pump shaft. If the equipped).impeller turns, the pump is OK. CAUTION: All 4.0L 6-cylinder engines have a re- verse (counter-clockwise) rotating water pump. The letter R is stamped into the back of the water pump impeller (Fig. 1) to identify. Engines from previous model years, depending upon application, may be equipped with a forward (clockwise) rotating water pump. Installation of the wrong water pump will cause engine over heating. The water pump impeller is pressed on the rear of the pump shaft and bearing assembly. The water pump is serviced only as a complete assembly. WARNING: DO NOT REMOVE THE BLOCK DRAIN PLUG(S) OR LOOSEN RADIATOR DRAINCOCK WITH THE SYSTEM HOT AND UNDER PRESSURE. SERIOUS BURNS FROM COOLANT CAN OCCUR. DO NOT WASTE reusable coolant. If the solution is clean, drain coolant into a clean container for re- use. (1) Disconnect negative battery cable at battery. (2) Drain the cooling system. Refer to Cooling Sys- Fig. 3 Impeller Test—Typical tem Draining in this group. Connect the hose and install the coolant, or proceed (3) Loosen (but do not remove at this time) thewith repairs. four fan hub-to-water pump pulley mounting nuts. The engine accessory drive belt must be removedINSPECTING FOR INLET RESTRICTIONS prior to removing the fan. Inadequate heater performance may be caused by a (4) Remove engine drive belt as follows:metal casting restriction in the water pump heater (a) Loosen two rear power steering pump mount-hose inlet. ing bolts A (Fig. 4).
ZJ COOLING SYSTEM SERVICE PROCEDURES 7 - 13 Fig. 6 Bracket Mounting Bolts—4.0L Engine E. Bracket mounting bolt E is located behind the power steering pump (Fig. 6). (7) Remove two bolts A (Fig. 4). (8) Remove locknut C and belt adjustment bolt DFig. 4 P.S. Pump Rear Mounting Bolts—4.0L Engine (Figs. 5 or 6). (9) Remove bolt B (Fig. 5). Position power steering (b) Loosen upper pump pivot bolt B and lower pump to the side. Hold pump in position with wire. lock nut C (Figs. 5 or 6). Do not disconnect hydraulic lines from pump. (10) Remove bolts E, F and G (Fig. 6) and remove pump mounting bracket. (11) Remove idler pulley mounting bolt and remove idler pulley. This must be done to gain clearance for the water pump mounted heater hose fitting when water pump is being removed. WARNING: CONSTANT TENSION HOSE CLAMPS ARE USED ON MOST COOLING SYSTEM HOSES. WHEN REMOVING OR INSTALLING, USE ONLY TOOLS DESIGNED FOR SERVICING THIS TYPE OF CLAMP, SUCH AS SPECIAL CLAMP TOOL (NUMBER 6094) (FIG. 7). SNAP-ON CLAMP TOOL (NUMBER HPC-20) MAY BE USED FOR LARGER CLAMPS. AL- WAYS WEAR SAFETY GLASSES WHEN SERVICING CONSTANT TENSION CLAMPS. CAUTION: A number or letter is stamped into the tongue of constant tension clamps (Fig. 8). If re- placement is necessary, use only an original equip- ment clamp with matching number or letter.Fig. 5 P.S. Pump Front Mounting Bolt/Locknut—4.0L Engine (12) Remove lower radiator hose from water pump. (c) Loosen pump adjusting bolt D (Fig. 4) until Remove heater hose from water pump fitting. belt can be removed. (13) Remove the four fan hub-to-water pump pul- (d) Remove belt. ley mounting nuts. (5) Check condition of all pulleys. (14) Remove the two fan shroud-to-upper radiator (6) The power steering pump must be removed crossmember attaching nuts (Fig. 9).from its cast mounting bracket to gain access to bolt (15) Remove the fan assembly and fan shroud (to- gether as one unit) from the vehicle.
7 - 14 COOLING SYSTEM SERVICE PROCEDURES ZJ Fig. 7 Hose Clamp Tool—Typical Fig. 9 Fan Shroud Mounting Fig. 8 Clamp Number/Letter Location (16) Remove the four pump mounting bolts (Fig.10) and remove pump from vehicle. Discard old gas-ket. Note that one of the four bolts is longer than theother bolts. (17) If pump is to be replaced, the heater hose fit-ting must be removed. Note position of fitting beforeremoval.INSTALLATION—4.0L 6-CYL. ENGINE (1) If pump is being replaced, install the heaterhose fitting to the pump. Use a sealant on the fitting Fig. 10 Water Pump Remove/Install—4.0L 6-Cylindersuch as Mopar™ Thread Sealant With Teflon. Refer Engineto the directions on the package. eign material. Inspect the cylinder block and water (2) Clean the gasket mating surfaces. If the origi- pump mating surfaces for erosion or damage fromnal pump is used, remove any deposits or other for- cavitation.
ZJ COOLING SYSTEM SERVICE PROCEDURES 7 - 15 (3) Install the gasket and water pump (the gasket (12) Position drive belt to pulleys.is installed dry). Tighten mounting bolts to 30 N⅐m (13) Tighten belt adjustment bolt D (Fig. 4) to the(22 ft. lbs.) torque. Rotate the shaft by hand to be proper tension. Refer to the Specifications section atsure it turns freely. the end of this group for belt tension. (4) Connect the radiator and heater hoses to the (14) Tighten bolts A (Fig. 4) to 27 N⅐m (20 ft. lbs.)water pump. torque. (5) Position the fan assembly and fan shroud (to- (15) Tighten pivot bolt B (Fig. 5) to 27 N⅐m (20 ft.gether as one unit) to the engine. lbs.) torque. (6) Position fan shroud to radiator. Be sure the (16) Tighten locknut C (Fig. 5) to 27 N⅐m (20 ft.alignment tabs at the lower part of shroud are placed lbs.) torque.into the slots near lower part of radiator. Install and (17) After the power steering pump has been tight-tighten the two fan shroud mounting nuts. ened, recheck belt tension. (7) Install fan assembly to water pump hub. (18) Fill cooling system with coolant and check forTighten fan drive mounting nuts to 24 N⅐m (18 ft. leaks. Refer to Refilling Cooling System in thislbs.) torque. Be sure of at least 25 mm (1.0 inches)between tips of fan blades and fan shroud. group. (8) Position power steering pump bracket to en- (19) Connect battery cable to battery.gine. Install bolts E, F and G (Fig. 6). Tighten bolts F (20) Start and warm the engine. Check for leaks.and G to 38 N⅐m (28 ft. lbs.) torque. Tighten bolt E to REMOVAL—5.2L V-8 ENGINE27 N⅐m (20 ft. lbs.) torque. The water pump on 5.2L engines is bolted directly (9) Position power steering pump to mountingbracket. Install pivot bolt B (Fig. 5) finger tight. In- to the engine timing chain case/cover.stall locknut C and adjustment bolt D (Figs. 5 or 6) A gasket is used as a seal between the water pumpfinger tight. and timing chain case/cover. (10) Install two adjustment bolts A (Fig. 4) finger If water pump is replaced because of bearing/shafttight. damage, or leaking shaft seal, the mechanical cooling (11) Install idler pulley. fan assembly should also be inspected. Inspect for fa- tigue cracks, loose blades, or loose rivets that couldCAUTION: When installing the serpentine engine have resulted from excessive vibration. Replace fan ifaccessory drive belt, the belt MUST be routed cor- any of these conditions are found. Also check condi-rectly. If not, the engine may overheat due to the tion of the thermal viscous fan drive. Refer to Viscouswater pump rotating in the wrong direction. Refer to Fan Drive in this group.figure 11 for appropriate belt routing. Or, refer to the The water pump on all models can be removedBelt Routing Label located in the engine compartment. without discharging the air conditioning system (if equipped). (1) Disconnect negative battery cable from battery. (2) Drain cooling system. Refer to Draining Cooling System in this group. Do not waste reusable coolant. If solution is clean, drain coolant into a clean container for reuse. (3) The thermal viscous fan drive is attached (threaded) to the water pump hub shaft (Fig. 12). Re- move fan/viscous fan drive assembly from water pump by turning mounting nut counterclockwise as viewed from front. Threads on viscous fan drive are RIGHT HAND. A Snap-On 36 MM Fan Wrench (number SP346 from Snap-On Cummins Diesel Tool Set number 2017DSP) can be used. Place a bar or screwdriver between water pump pulley bolts (Fig. 12) to prevent pulley from rotating. Do not attempt to remove fan/viscous fan drive assembly from vehi- cle at this time. Fig. 11 Belt Routing—4.0L 6-Cylinder Engine
7 - 16 COOLING SYSTEM SERVICE PROCEDURES ZJ Fig. 12 Fan Blade and Viscous Fan Drive—5.2L Fig. 13 Fan Shroud Nuts Engine rotating tensioner clockwise (as viewed from front)WARNING: CONSTANT TENSION HOSE CLAMPS (Fig. 14). When all belt tension has been relaxed, re-ARE USED ON MOST COOLING SYSTEM HOSES. move accessory drive belt.WHEN REMOVING OR INSTALLING, USE ONLYTOOLS DESIGNED FOR SERVICING THIS TYPE OFCLAMP, SUCH AS SPECIAL CLAMP TOOL (NUMBER6094) (FIG. 7). SNAP-ON CLAMP TOOL (NUMBERHPC-20) MAY BE USED FOR LARGER CLAMPS. AL-WAYS WEAR SAFETY GLASSES WHEN SERVICINGCONSTANT TENSION CLAMPS.CAUTION: A number or letter is stamped into thetongue of constant tension clamps (Fig. 8). If re-placement is necessary, use only an original equip-ment clamp with matching number or letter. (4) If water pump is being replaced, do not unboltfan blade assembly (Fig. 12) from thermal viscousfan drive. (5) Remove two fan shroud-to-radiator nuts (Fig.13). Do not attempt to remove fan shroud at thistime. (6) Remove fan shroud and fan blade/viscous fandrive assembly from vehicle as a complete unit. After removing fan blade/viscous fan drive assem-bly, do not place thermal viscous fan drive in hori- Fig. 14 Belt Tensioner Assembly—5.2L Enginezontal position. If stored horizontally, silicone fluid in (8) Remove four water pump pulley-to-water pumpviscous fan drive could drain into its bearing assem- hub bolts (Fig. 12) and remove pulley from vehicle.bly and contaminate lubricant. (9) Remove lower radiator hose clamp and remove Do not remove water pump pulley bolts at this lower hose at water pump.time. (10) Remove heater hose clamp (Fig. 15) and (7) Remove accessory drive belt as follows: Thedrive belt is equipped with a spring loaded automatic heater hose from heater hose coolant return tube.belt tensioner (Fig. 14). Relax tension from belt by
ZJ COOLING SYSTEM SERVICE PROCEDURES 7 - 17 (11) Loosen heater hose coolant return tube mount- INSPECTIONing bolt and nut (Fig. 15) and remove tube from wa- Replace water pump assembly if it has any of theter pump. Discard the old tube o-ring. following conditions: • The body is cracked or damaged • Water leaks from shaft seal. This is evident by traces of coolant below vent hole • Loose or rough turning bearing. Also inspect vis- cous fan drive • Impeller rubs either the pump body or timing chain case/cover INSTALLATION—5.2L V-8 ENGINE (1) Clean gasket mating surfaces. (2) Using a new gasket, install water pump to en- gine as follows: Guide water pump nipple into bypass hose as pump is being installed. Install water pump bolts (Fig. 16). Tighten water pump mounting bolts to 40 N⅐m (30 ft. lbs.) torque. (3) Position bypass hose clamp to bypass hose. (4) Spin water pump to be sure that pump impeller does not rub against timing chain case/cover. (5) Install a new o-ring to the heater hose coolant return tube (Fig. 15). Coat the new o-ring with anti- freeze before installation. Fig. 15 Coolant Return Tube—5.2L Engine (6) Install coolant return tube to engine (Fig. 15). Be sure the slot in tube bracket is bottomed to the (12) Remove seven water pump mounting bolts mounting bolt. This will properly position return(Fig. 16). tube. (7) Connect radiator lower hose to water pump. (8) Connect heater hose and hose clamp to coolant return tube. (9) Install water pump pulley. Tighten bolts to 27 N⅐m (20 ft. lbs.) torque. Place a bar or screwdriver between water pump pulley bolts (Fig. 12) to prevent pulley from rotating. (10) Relax tension from belt tensioner (Fig. 14). In- stall drive belt. CAUTION: When installing the serpentine accessory drive belt, belt must be routed correctly. If not, en- gine may overheat due to water pump rotating in wrong direction. Refer to (Fig. 17) for correct belt routing. Or, refer to the Belt Routing Label located in the engine compartment. The correct belt with Fig. 16 Water Pump Bolts—5.2L Engine—Typical correct length must be used. (13) Loosen clamp at water pump end of bypass (11) Position fan shroud and fan blade/viscous fanhose (Fig. 12). Slip bypass hose from water pump drive assembly to vehicle as a complete unit.while removing pump from vehicle. Discard old gas- Be sure the upper and lower portions of the fanket. shroud are firmly connected. All air must flow through the radiator.CAUTION: Do not pry water pump at timing chain (12) Install two fan shroud-to-radiator nuts (Fig.case/cover. The machined surfaces may be dam- 13).aged resulting in leaks. Be sure of at least 25 mm (1.0 inches) between tips of fan blades and fan shroud. (13) Install fan blade/viscous fan drive assembly to water pump shaft.
7 - 18 COOLING SYSTEM SERVICE PROCEDURES ZJ WITHOUT AIR CONDITIONING (A/C) REMOVAL (1) Partially drain cooling system. Refer to Drain- ing Cooling System in this group. Do not waste reusable coolant. If solution is clean, drain coolant into a clean container for reuse. WARNING: CONSTANT TENSION HOSE CLAMPS ARE USED ON MOST COOLING SYSTEM HOSES. WHEN REMOVING OR INSTALLING, USE ONLY TOOLS DESIGNED FOR SERVICING THIS TYPE OF CLAMP, SUCH AS SPECIAL CLAMP TOOL (NUMBER 6094) (FIG. 19). SNAP-ON CLAMP TOOL (NUMBER HPC-20) MAY BE USED FOR LARGER CLAMPS. AL- WAYS WEAR SAFETY GLASSES WHEN SERVICING CONSTANT TENSION CLAMPS. CAUTION: A number or letter is stamped into the tongue of constant tension clamps (Fig. 20). If re- placement is necessary, use only an original equip- Fig. 17 Belt Routing—5.2L Engine ment clamp with matching number or letter. (14) Fill cooling system. Refer to Refilling the Cool-ing System in this group. (15) Connect negative battery cable. (16) Start and warm the engine. Check for leaks.WATER PUMP BYPASS HOSE—5.2L V-8 ENGINE A water pump bypass hose (Fig. 18) is used be-tween the intake manifold and water pump on all5.2L V-8 engines. To test for leaks, refer to TestingCooling System for Leaks in this group. Fig. 19 Hose Clamp Tool—Typical (2) Loosen both bypass hose clamps (Fig. 19) and position to center of hose. Remove hose from vehicle. INSTALLATION (1) Position bypass hose clamps (Fig. 19) to center of hose. (2) Install bypass hose to engine. (3) Secure both hose clamps (Fig. 19). (4) Fill cooling system. Refer to Refilling the Cool- ing System in this group. (5) Start and warm the engine. Check for leaks. WITH AIR CONDITIONING (A/C) REMOVAL Fig. 18 Water Pump Bypass Hose—5.2L Engine If equipped with A/C, the generator and A/C com- pressor along with their common mounting bracket
ZJ COOLING SYSTEM SERVICE PROCEDURES 7 - 19 (1) Disconnect negative battery cable from battery. (2) Partially drain cooling system. Refer to Drain- ing Cooling System in this group. Do not waste reusable coolant. If solution is clean, drain coolant into a clean container for reuse. (3) Remove upper radiator hose clamp (Fig. 19) and hose at radiator. (4) Unplug wiring harness from A/C compressor. (5) Remove air duct at throttle body. (6) Disconnect A/C lines from clip at intake mani- fold. (7) Remove heater hose coolant return tube mount- ing bolt and nut (Fig. 22). Remove tube from engine and discard the old tube o-ring. Fig. 20 Clamp Number/Letter Location(Fig. 21) must be partially removed. Removing gener-ator or A/C compressor from their mounting bracketis not necessary. Also, discharging A/C system is notnecessary. Do not remove any refrigerant lines fromA/C compressor. Fig. 22 Coolant Return Tube—5.2L Engine (8) Remove accessory drive belt as follows: The drive belt is equipped with a spring loaded automatic belt tensioner (Fig. 23). Relax tension from belt by rotating tensioner clockwise (as viewed from front) (Fig. 23). When all belt tension has been relaxed, re- move accessory drive belt. (9) The drive belt idler pulley must be removed to gain access to one of A/C compressor/generator bracket mounting bolts. Remove idler pulley bolt and remove idler pulley (Fig. 21). (10) Remove oil dipstick tube mounting bolt at side of A/C-generator mounting bracket. Fig. 21 Generator and A/C Compressor Mounting (11) Disconnect speed control cable and throttle ca- Bracket—5.2L Engine ble at throttle body. Refer to Accelerator Pedal and Throttle Cable in Group 14, Fuel System for throttleWARNING: THE A/C SYSTEM IS UNDER PRESSURE cable removal and installation. Refer to Group 8H forEVEN WITH ENGINE OFF. REFER TO REFRIGER- removal and installation of speed control cable.ANT WARNINGS IN GROUP 24, HEATING AND AIR (12) Remove bracket-to-intake manifold boltsCONDITIONING. (number 1 and 2—figure 21).
7 - 20 COOLING SYSTEM SERVICE PROCEDURES ZJ wrong direction. Refer to figure 24 for correct belt routing. Or, refer to the Belt Routing Label located in the engine compartment. The correct belt with correct length must be used. Fig. 23 Belt Tensioner Assembly—5.2L Engine (13) Remove six bracket bolts (number 3—figure21). (14) Lift and position generator and A/C compres-sor (along with their common mounting bracket) to Fig. 24 Belt Routing—5.2L Enginegain access to bypass hose. A block of wood may be (11) Install air duct to throttle body.used to hold assembly in position. (12) Install upper radiator hose to radiator. (15) Loosen and position both hose clamps to cen- (13) Connect wiring harness to A/C compressor.ter of bypass hose. Remove hose from vehicle. (14) Connect A/C lines to clip at intake manifold. (15) Fill cooling system. Refer to Refilling the Cool-INSTALLATION ing System in this group. (1) Position bypass hose clamps to center of hose. (16) Start and warm the engine. Check for leaks. (2) Install bypass hose to engine. (3) Secure both hose clamps (Fig. 19). THERMOSTAT (4) Install generator-A/C mounting bracket assem-bly to engine. Tighten bolts (number 1 and 2—figure DESCRIPTION AND OPERATION21) to 54 N⅐m (40 ft. lbs.) torque. Tighten bolts (num- A pellet-type thermostat controls the operatingber 3—figure 21) to 40 N⅐m (30 ft. lbs.) torque. temperature of the engine by controlling the amount (5) Install a new o-ring to the heater hose coolant of coolant flow to the radiator. On all engines thereturn tube (Fig. 22). Coat the new o-ring with anti- thermostat is closed below 195°F (90°C). Above thisfreeze before installation. temperature, coolant is allowed to flow to the radia- (6) Install coolant return tube to engine (Fig. 22). tor. This provides quick engine warm up and overall Be sure the slot in tube bracket is bottomed to the temperature control.mounting bolt. This will properly position return An arrow, plus the word UP is stamped on thetube. front flange next to the air bleed. The words TO (7) Connect throttle body control cables. RAD are stamped on one arm of the thermostat. (8) Install oil dipstick mounting bolt. They indicate the proper installed position. (9) Install idler pulley. Tighten pulley bolt to 54 The same thermostat is used for winter and sum-N⅐m (40 ft. lbs.) torque. mer seasons. An engine should not be operated with- (10) Relax tension from belt tensioner (Fig. 23). In- out a thermostat, except for servicing or testing.stall drive belt. Operating without a thermostat causes other prob- lems. These are: longer engine warmup time, unreli-CAUTION: When installing serpentine accessory able warmup performance, increased exhaustdrive belt, belt must be routed correctly. If not, en- emissions and crankcase condensation. This conden-gine may overheat due to water pump rotating in sation can result in sludge formation.
ZJ COOLING SYSTEM SERVICE PROCEDURES 7 - 21CAUTION: Do not operate an engine without a ther- CAUTION: A number or letter is stamped into themostat, except for servicing or testing. tongue of constant tension clamps (Fig. 20). If re- placement is necessary, use only an original equip- The more common type of thermostat failure, usu- ment clamp with matching number or letter.ally found on high milage vehicles, is a thermostatfailed in the shut position. The temperature gauge (if (2) Remove radiator upper hose and heater hose atequipped) will give an indication of this condition. thermostat housing.Depending upon length of time that vehicle is oper- (3) Disconnect wiring connector at engine coolantated, pressure cap may vent. This will expel steam temperature sensor.and coolant to coolant reserve/overflow tank and to (4) Remove thermostat housing mounting bolts,surface below vehicle. Refer to the Diagnosis section thermostat housing, gasket and thermostat (Fig. 25).of this group. Discard old gasket.ON-BOARD DIAGNOSTICSFOR CERTAIN COOLING SYSTEM COMPONENTS All models are equipped with On-Board Diagnosticsfor certain cooling system components. Refer to On-Board Diagnostics (OBD) in the Diagnosis section ofthis group for additional information. If the power-train control module (PCM) detects low engine cool-ant temperature, it will record a Diagnostic TroubleCode (DTC) in the PCM memory. The DTC numberfor low coolant temperature is 17. Do not change athermostat for lack of heat as indicated by the in-strument panel gauge or heater performance unless aDTC number 17 is present. Refer to the Diagnosissection of this group for other probable causes. Forother DTC numbers, refer to On-Board Diagnosticsin the General Diagnosis section of Group 14, FuelSystems. The DTC can also be accessed through the DRBscan tool. Refer to the appropriate Powertrain Diag-nostic Procedures manual for diagnostic informationand operation of the DRB scan tool. Fig. 25 Thermostat Removal/Installation—4.0L EngineREMOVAL—4.0L 6-CYLINDER ENGINE (5) Clean the gasket mating surfaces.WARNING: DO NOT LOOSEN THE RADIATORDRAINCOCK WITH THE SYSTEM HOT AND PRES- INSTALLATION—4.0L 6-CYLINDER ENGINESURIZED. SERIOUS BURNS FROM THE COOLANT (1) Install the replacement thermostat so that theCAN OCCUR. pellet, which is encircled by a coil spring, faces the engine. All thermostats are marked on the outer DO NOT WASTE reusable coolant. If the solution flange to indicate the proper installed position.is clean, drain the coolant into a clean container for (a) Observe the recess groove in the engine cylin-reuse. der head (Fig. 26). (1) Drain the coolant from the radiator until the (b) Position thermostat in groove with arrow andlevel is below the thermostat housing. air bleed hole on outer flange pointing up. (2) Install replacement gasket and thermostatWARNING: CONSTANT TENSION HOSE CLAMPS housing.ARE USED ON MOST COOLING SYSTEM HOSES.WHEN REMOVING OR INSTALLING, USE ONLY CAUTION: Tightening the thermostat housing un-TOOLS DESIGNED FOR SERVICING THIS TYPE OF evenly or with the thermostat out of its recess, mayCLAMP, SUCH AS SPECIAL CLAMP TOOL (NUMBER result in a cracked housing.6094) (FIG. 19). SNAP-ON CLAMP TOOL (NUMBERHPC-20) MAY BE USED FOR LARGER CLAMPS. AL- (3) Tighten the housing bolts to 22 N⅐m (16 ft. lbs.)WAYS WEAR SAFETY GLASSES WHEN SERVICING torque.CONSTANT TENSION CLAMPS. (4) Install hoses to thermostat housing.
7 - 22 COOLING SYSTEM SERVICE PROCEDURES ZJ Fig. 26 Thermostat Recess—4.0L Engine Fig. 27 Generator Support Bracket—5.2L Engine (5) Install electrical connector to coolant tempera- bolt of automatic belt tensioner (Fig. 28).ture sensor. (c) Rotate tensioner assembly clockwise (as (6) Be sure that the radiator draincock is tightly viewed from front) until tension has been relievedclosed. Fill the cooling system to the correct level from belt.with the required coolant mixture. Refer to RefillingCooling System in this group. (7) Start and warm the engine. Check for leaks.REMOVAL—5.2L V-8 ENGINEWARNING: DO NOT LOOSEN RADIATOR DRAIN-COCK WITH SYSTEM HOT AND PRESSURIZED. SE-RIOUS BURNS FROM COOLANT CAN OCCUR. Do not waste reusable coolant. If solution is clean,drain coolant into a clean container for reuse. If thermostat is being replaced, be sure that re-placement is specified thermostat for vehicle modeland engine type. Factory installed thermostat housings on 5.2L en-gines are installed on a gasket with an anti-stickcoating. This will aid in gasket removal and clean-up. (1) Disconnect negative battery cable at battery. (2) Drain cooling system until coolant level is be-low thermostat. Refer to Draining Cooling System inthis group. (3) Air Conditioned vehicles: Remove supportbracket (generator mounting bracket-to-intake mani- Fig. 28 Automatic Belt Tensioner—5.2L Enginefold) located near rear of generator (Fig. 27). (4) On air conditioning equipped vehicles, the gen- (d) Remove belt from vehicle.erator must be partially removed. (e) Remove two generator mounting bolts. Do not (a) Remove generator drive belt as follows: Drive remove any wiring at generator. If equipped with belts on the 5.2L engine are equipped with a spring 4WD, unplug 4WD indicator lamp wiring harness loaded automatic belt tensioner (Fig. 28). (located near rear of generator). (b) Attach a socket/wrench to pulley mounting
ZJ COOLING SYSTEM SERVICE PROCEDURES 7 - 23 (f) Remove generator. Position generator to gain access for thermostat gasket removal. (5) Remove upper radiator hose clamp (Fig. 19)and upper radiator hose at thermostat housing. (6) Position wiring harness (behind thermostathousing) to gain access to thermostat housing. (7) Remove thermostat housing mounting bolts,thermostat housing, gasket and thermostat (Fig. 29).Discard old gasket. Fig. 30 Thermostat Position—5.2L Engine (a) Install generator. Tighten bolts to 41 N⅐m (30 ft. lbs.) torque. (b) Install support bracket (generator mounting bracket-to-intake manifold) (Fig. 27). Tighten bolts to 54 N⅐m (40 ft. lbs.) torque. CAUTION: When installing the serpentine accessory drive belt, belt must be routed correctly. If not, en- Fig. 29 Thermostat—5.2L Engine gine may overheat due to water pump rotating in wrong direction. Refer to (Fig. 31) for correct 5.2LINSTALLATION—5.2L V-8 ENGINE engine belt routing. Or, refer to the Belt Routing La- (1) Clean mating areas of intake manifold and bel located in the engine compartment. The correctthermostat housing. belt with correct length must be used. (2) Install thermostat (spring side down) into re-cessed machined groove on intake manifold (Fig. 29). (c) Position drive belt over all pulleys except (3) Install gasket on intake manifold and over idler pulley (located between generator and A/Cthermostat (Fig. 29). compressor). (4) Position thermostat housing to intake manifold. (d) Attach a socket/wrench to pulley mountingNote the word FRONT stamped on housing (Fig. 30). bolt of automatic belt tensioner (Fig. 28).For adequate clearance, this must be placed towards (e) Rotate socket/wrench clockwise. Place beltfront of vehicle. The housing is slightly angled for- over idler pulley. Let tensioner rotate back intoward after installation to intake manifold. place. Remove wrench. Be sure belt is properly (5) Install two housing-to-intake manifold bolts. seated on all pulleys.Tighten bolts to 23 N⅐m (200 in. lbs.) torque. (8) Fill cooling system. Refer to Refilling Cooling System in this group.CAUTION: Housing must be tightened evenly and (9) Connect negative battery cable to battery.thermostat must be centered into recessed groove (10) Start and warm the engine. Check for leaks.in intake manifold. If not, it may result in a crackedhousing, damaged intake manifold threads or cool- COOLANTant leak. GENERAL INFORMATION (6) Install upper radiator hose to thermostat hous- The cooling system is designed around the coolant.ing. Coolant flows through the engine water jackets ab- (7) Air Conditioned vehicles: sorbing heat produced during engine operation. The
7 - 24 COOLING SYSTEM SERVICE PROCEDURES ZJ centage of antifreeze can cause the engine to over- heat because specific heat of antifreeze is lower than that of water. CAUTION: Richer antifreeze mixtures cannot be measured with normal field equipment and can cause problems associated with 100 percent ethyl- ene-glycol. COOLANT SELECTION-ADDITIVES Coolant should be maintained at the specified level with a mixture of ethylene glycol-based antifreeze and low mineral content water. Only use an anti- freeze containing ALUGARD 340-2 ™. CAUTION: Do not use coolant additives that are claimed to improve engine cooling. COOLANT SERVICE It is recommended that the cooling system be Fig. 31 Belt Routing—5.2L Engine drained and flushed at 84,000 kilometers (52,500 miles), or 3 years, whichever occurs first. Then everycoolant carries heat to the radiator and heater core. two years, or 48,000 kilometers (30,000 miles),Here it is transferred to ambient air passing through whichever occurs first.the radiator and heater core fins. The coolant also re-moves heat from the automatic transmission fluid in COOLANT LEVEL CHECK-ROUTINEvehicles equipped with an automatic transmission. Do not remove radiator cap for routine cool- ant level inspections. The coolant level can beCOOLANT PERFORMANCE checked at coolant reserve/overflow tank. The required ethylene-glycol (antifreeze) and water The coolant reserve/overflow system provides amixture depends upon climate and vehicle operating quick visual method for determining coolant levelconditions. The coolant performance of various mix- without removing radiator pressure cap. With enginetures follows: idling and at normal operating temperature, observe Pure Water-Water can absorb more heat than a coolant level in reserve/overflow tank. The coolantmixture of water and ethylene-glycol. This is for pur- level should be between ADD and FULL marks.pose of heat transfer only. Water also freezes at ahigher temperature and allows corrosion. ADDING ADDITIONAL COOLANT-ROUTINE 100% Ethylene-Glycol-The corrosion inhibiting Do not remove radiator cap to add coolant to system. When adding coolant to maintain correctadditives in ethylene-glycol need the presence of wa- level, do so at coolant reserve/overflow tank. Use ater to dissolve. Without water, additives form depos- 50/50 mixture of ethylene-glycol antifreeze containingits in system. These act as insulation causing Alugard 340-2 ™ and low mineral content water. Re-temperature to rise to as high as 149°C (300°F). This move radiator cap only for testing or when refillingtemperature is hot enough to melt plastic and soften system after service. Removing cap unnecessarily cansolder. The increased temperature can result in en- cause loss of coolant and allow air to enter system,gine detonation. In addition, 100 percent ethylene- which produces corrosion.glycol freezes at -22°C (-8°F). 50/50 Ethylene-Glycol and Water-Is the recom- COOLANT LEVEL CHECK-SERVICEmended mixture, it provides protection against freez- The cooling system is closed and designed to main-ing to -37°C (-35°F). The antifreeze concentration tain coolant level to top of radiator.must always be a minimum of 44 percent, year-round in all climates. If percentage is lower, engine WARNING: DO NOT OPEN RADIATOR DRAINCOCKparts may be eroded by cavitation. Maximum protec- WITH ENGINE RUNNING OR WHILE ENGINE IS HOTtion against freezing is provided with a 68 percent AND COOLING SYSTEM IS UNDER PRESSURE.antifreeze concentration, which prevents freezingdown to -67.7°C (-90°F). A higher percentage will When vehicle servicing requires a coolant levelfreeze at a warmer temperature. Also, a higher per- check in radiator, drain several ounces of coolant
ZJ COOLING SYSTEM SERVICE PROCEDURES 7 - 25from radiator drain cock. Do this while observing (2) Attach one end of a hose to the draincock. Putcoolant reserve/overflow system tank. The coolant the other end into a clean container. Open draincocklevel in reserve/overflow tank should drop slightly. If and drain coolant from radiator. This will empty thenot, inspect for a leak between radiator and coolant coolant reserve/overflow tank. The coolant does notreserve/overflow system connection. Remove radiator have to be removed from the tank unless the systemcap. The coolant level should be to top of radiator. If is being refilled with a fresh mixture. When tank isnot and if coolant level in reserve/overflow tank is at empty, remove radiator cap and continue drainingADD mark, check for: cooling system.• An air leak in coolant reserve/overflow tank or its To drain the 4.0L 6-cylinder engine of coolant, re-hose move the cylinder block drain plug located on the• An air leak in radiator filler neck side of cylinder block (Fig. 32).• Leak in pressure cap seal to radiator filler neck To drain the 5.2L V-8 engine of coolant, remove the cylinder block drain plugs located on the sides of cyl-LOW COOLANT LEVEL-AERATION inder block above the oil pan rail (Fig. 33). If the coolant level in radiator drops below top ofradiator core tubes, air will enter cooling system. Low coolant level can cause thermostat pellet to besuspended in air instead of coolant. This will causethermostat to open later, which in turn causes highercoolant temperature. Air trapped in cooling systemalso reduces amount of coolant circulating in heatercore resulting in low heat output.DEAERATION As the engine operates, any air trapped in coolingsystem gathers under the radiator cap. The next timethe engine is operated, thermal expansion of coolantwill push any trapped air past radiator cap into thecoolant reserve/overflow tank. Here it escapes to theatmosphere into the tank. When the engine coolsdown the coolant, it will be drawn from the reserve/overflow tank into the radiator to replace any re-moved air.DRAINING COOLING SYSTEMWARNING: DO NOT REMOVE THE CYLINDER Fig. 32 Drain Plug—4.0L 6-Cylinder EngineBLOCK DRAIN PLUGS OR LOOSEN THE RADIATORDRAINCOCK WITH SYSTEM HOT AND UNDERPRESSURE. SERIOUS BURNS FROM COOLANTCAN OCCUR. DO NOT WASTE reusable coolant. If the solutionis clean, drain the coolant into a clean container forreuse.DRAINING ENTIRE SYSTEM Use this procedure if the entire cooling system is tobe drained, such as for engine removal. (1) DO NOT remove radiator cap first. With enginecold, raise vehicle on a hoist and locate radiatordraincock.• 4.0L 6-cyl. Engine: Radiator draincock is locatedon the right/lower side of radiator facing to rear of Fig. 33 Drain Plugs—5.2L V-8 Enginevehicle.• 5.2L V-8 Engine: Radiator draincock is located on PARTIAL DRAININGthe left/lower side of radiator facing to rear of vehi- Use this procedure if the coolant is to be partiallycle. drained, such as for engine thermostat removal.
7 - 26 COOLING SYSTEM SERVICE PROCEDURES ZJ (1) With engine cold, slowly remove the radiator REVERSE FLUSHING RADIATORcap. Raise vehicle on a hoist and locate radiator Disconnect the radiator hoses from the radiator fit-draincock. tings. Attach a section of radiator hose to the radia-• 4.0L Engine: Radiator draincock is located on the tor bottom outlet fitting and insert the flushing gun.right/lower side of radiator facing to rear of vehicle. Connect a water supply hose and air supply hose to• 5.2L Engine: Radiator draincock is located on the the flushing gun.left/lower side of radiator facing to rear of vehicle. CAUTION: The cooling system normally operates at (2) Attach one end of a hose to the draincock. Put 97-to-124 kPa (14-to-18 psi) pressure. Exceedingthe other end into a clean container. this pressure may damage the radiator or hoses. (3) Open draincock and drain desired amount ofcoolant from radiator. Allow the radiator to fill with water. When radiator is filled, apply air in short blasts allowing radiator toREFILLING COOLING SYSTEM refill between blasts. Continue this reverse flushing (1) Tighten the radiator draincock and the cylinder until clean water flows out through rear of radiatorblock drain plug(s) (if removed). cooling tube passages. For more information, refer to (2) Fill system using a 50/50 mixture of water and operating instructions supplied with flushing equip-antifreeze as described in the Coolant Section of this ment. Have radiator cleaned more extensively by agroup. Fill radiator to top and install radiator cap. radiator repair shop.Add sufficient coolant to the reserve/overflow tank toraise level to FULL mark. REVERSE FLUSHING ENGINE (3) With heater control unit in the HEAT position, Drain the cooling system. Remove the thermostatoperate engine with radiator cap in place. housing and thermostat. Install the thermostat hous- (4) After engine has reached normal operating ing. Disconnect the radiator upper hose from the ra-temperature, shut engine off and allow it to cool. diator and attach the flushing gun to the hose. Disconnect the radiator lower hose from the waterWhen engine is cooling down, coolant will be drawn pump. Attach a lead away hose to the water pumpinto the radiator from the reserve/overflow tank. inlet fitting. (5) Add coolant to reserve/overflow tank as neces- Connect the water supply hose and air supply hosesary. Only add coolant to the reserve/overflow to the flushing gun. Allow the engine to fill with wa-tank when the engine is cold. Coolant level in a ter. When the engine is filled, apply air in shortwarm engine will be higher due to thermal ex- blasts, allowing the system to fill between air blasts.pansion. To purge the cooling system of all air, this Continue until clean water flows through the leadheat up/cool down cycle (adding coolant to cold en- away hose. For more information, refer to operatinggine) must be performed three times. Add necessary instructions supplied with flushing equipment.coolant to raise tank level to the FULL mark after Remove the lead away hose, flushing gun, watereach cool down period. supply hose and air supply hose. Remove the thermo- stat housing and install thermostat. Install the ther-COOLING SYSTEM CLEANING/REVERSE FLUSHING mostat housing with a replacement gasket. Refer to Thermostat Replacement. Connect the radiatorCAUTION: The cooling system normally operates at hoses. Refill the cooling system with the correct an-97-to-124 kPa (14-to-18 psi) pressure. Exceeding tifreeze/water mixture.this pressure may damage the radiator or hoses. CHEMICAL CLEANING In some instances, use a radiator cleaner (MoparCLEANING Radiator Kleen or equivalent) before flushing. This Drain cooling system and refill with water. Run en- will soften scale and other deposits and aid the flush-gine with radiator cap installed until upper radiator ing operation.hose is hot. Stop engine and drain water from sys-tem. If water is dirty, fill system with water, run en- CAUTION: Be sure instructions on the container aregine and drain system. Repeat until water drains followed.clean.REVERSE FLUSHING TESTING COOLING SYSTEM FOR LEAKS Reverse flushing of the cooling system is the forc-ing of water through the cooling system. This is done ULTRAVIOLET LIGHT METHODusing air pressure in the opposite direction of normal All Jeep models have a leak detection additivecoolant flow. It is usually only necessary with very added to the cooling system before they leave the fac-dirty systems with evidence of partial plugging. tory. The additive is highly visible under ultraviolet
ZJ COOLING SYSTEM SERVICE PROCEDURES 7 - 27light (black light). If the factory original coolant has Attach pressure tester 7700 (or an equivalent) tobeen drained, pour one ounce of additive into the the radiator filler neck (Fig. 35).cooling system. The additive is available through thepart’s department. Place the heater control unit inHEAT position. Start and operate the engine untilthe radiator upper hose is warm to the touch. Aimthe commercially available black light tool at thecomponents to be checked. If leaks are present, theblack light will cause the additive to glow a brightgreen color. The black light can be used along with a pressuretester to determine if any external leaks exist (Fig.34). Fig. 35 Pressurizing System—Typical Operate the tester pump to apply 124 kPa (18 psi) pressure to the system. If the hoses enlarge exces- sively or bulge while testing, replace as necessary. Observe the gauge pointer and determine the condi- tion of the cooling system according to the following criteria: • Holds Steady: If the pointer remains steady for two minutes, there are no serious coolant leaks in the system. However, there could be an internal leak that does not appear with normal system test pres- sure. Inspect for interior leakage or do the Internal Leakage Test. Do this if it is certain that coolant is being lost and no leaks can be detected. • Drops Slowly: Shows a small leak or seepage is oc- curring. Examine all connections for seepage or slight Fig. 34 Leak Detection Using Black Light—Typical leakage with a flashlight. Inspect the radiator, hoses, gasket edges and heater. Seal any small leak holesPRESSURE TESTER METHOD with a Sealer Lubricant or equivalent. Repair leak The engine should be at the normal operating tem- holes and reinspect the system with pressure ap-perature. Recheck the system cold if the cause of plied.coolant loss is not located during warm engine exam- • Drops Quickly: Shows that a serious leakage is oc-ination. curring. Examine the system for serious externalWARNING: HOT, PRESSURIZED COOLANT CAN leakage. If no leaks are visible, inspect for internalCAUSE INJURY BY SCALDING. leakage. Large radiator leak holes should be repaired by a reputable radiator repair shop. Carefully remove the radiator pressure cap fromthe filler neck and check the coolant level. Push INTERNAL LEAKAGE INSPECTIONdown on the cap to disengage it from the stop tabs. Remove the oil pan drain plug and drain a smallWipe the inner part of the filler neck and examine amount of engine oil. Coolant, being heavier, willthe lower inside sealing seat for nicks, cracks, paint, drain first, or operate engine to churn oil, then exam-dirt and solder residue. Inspect the reserve/overflow ine dipstick for water globules. Inspect the transmis-tank tube for internal obstructions. Insert a wire sion dipstick for water globules. Inspect thethrough the tube to be sure it is not obstructed. transmission fluid cooler for leakage. Operate the en- Inspect the cams on the outside part of the filler gine without the pressure cap on the radiator untilneck. If the cams are bent, seating of pressure cap thermostat opens.valve and tester seal will be affected. Replace cap ifcams are bent.
7 - 28 COOLING SYSTEM SERVICE PROCEDURES ZJ Attach a Pressure Tester to the filler neck. If pres- Start the engine and accelerate rapidly three timessure builds up quickly, a leak exists as result of a (to approximately 3000 rpm) while observing thefaulty cylinder head gasket or crack in the engine. coolant. If internal engine combustion gases are leak-Repair as necessary. ing into the cooling system, bubbles will appear in the coolant. If bubbles do not appear, there is no in-WARNING: DO NOT ALLOW PRESSURE TO EX- ternal combustion gas leakage.CEED 124 KPA (18 PSI). TURN THE ENGINE OFF.TO RELEASE THE PRESSURE, ROCK THE TESTER COOLANT RESERVE/OVERFLOW SYSTEMFROM SIDE TO SIDE. WHEN REMOVING THE This system works along with the radiator pressureTESTER, DO NOT TURN THE TESTER MORE THAN cap. This is done by using thermal expansion and1/2 TURN IF THE SYSTEM IS UNDER PRESSURE. contraction of the coolant to keep the coolant free of trapped air. It provides: If there is no immediate pressure increase, pump • A volume for coolant expansion and contraction.the Pressure Tester until the indicated pressure is • A convenient and safe method for checking/adjust-within the system range. Vibration of the gauge ing coolant level at atmospheric pressure. This ispointer indicates compression or combustion leakage done without removing the radiator pressure cap.into the cooling system. • Some reserve coolant to the radiator to cover mi- nor leaks and evaporation or boiling losses.WARNING: DO NOT DISCONNECT THE SPARK As the engine cools, a vacuum is formed in thePLUG WIRES WHILE THE ENGINE IS OPERATING. cooling system of both the radiator and engine. Cool- ant will then be drawn from the coolant tank and re-CAUTION: Do not operate the engine with a spark turned to a proper level in the radiator.plug shorted for more than a minute. The catalytic The coolant reserve/overflow system has a radiator mounted pressurized cap, an overflow tube and aconverter may be damaged. plastic coolant reserve/overflow tank (Fig. 36) Isolate the compression leak by shorting each mounted to the right inner fender.spark plug to the cylinder block. The gauge pointershould stop or decrease vibration when spark plugfor leaking cylinder is shorted. This happens becauseof the absence of combustion pressure.COMBUSTION LEAKAGE TEST (WITHOUTPRESSURE TESTER) DO NOT WASTE reusable coolant. If the solutionis clean, drain the coolant into a clean container forreuse.WARNING: DO NOT REMOVE THE CYLINDERBLOCK DRAIN PLUGS OR LOOSEN THE RADIATORDRAINCOCK WITH THE SYSTEM HOT AND UNDERPRESSURE. SERIOUS BURNS FROM COOLANTCAN OCCUR. Drain sufficient coolant to allow for thermostat re-moval. Refer to Thermostat Replacement. Disconnectthe water pump drive belt. Disconnect the upper radiator hose from the ther- Fig. 36 Coolant Reserve/Overflow Tank—Typicalmostat housing. Remove the housing and thermostat.Install the thermostat housing. RADIATOR PRESSURE CAP Add coolant to the radiator to bring the level to All radiators are equipped with a pressure cap.within 6.3 mm (1/4 in) of the top of the thermostat This cap releases pressure at some point within ahousing. range of 97-to-124 kPa (14-to-18 psi). The pressure relief point (in pounds) is engraved on top of the capCAUTION: Avoid overheating. Do not operate the (Fig. 37).engine for an excessive period of time. Open the The cooling system will operate at pressuresdraincock immediately after the test to eliminate slightly above atmospheric pressure. This results in aboil over of coolant. higher coolant boiling point allowing increased radi-
ZJ COOLING SYSTEM SERVICE PROCEDURES 7 - 29ator cooling capacity. The cap (Fig. 37) contains a WARNING: THE WARNING WORDS —DO NOTspring-loaded pressure relief valve. This valve opens OPEN HOT— ON THE RADIATOR PRESSURE CAPwhen system pressure reaches the release range of (FIG. 37) ARE A SAFETY PRECAUTION. WHEN HOT,97-to-124 kPa (14-to-18 psi). PRESSURE BUILDS UP IN COOLING SYSTEM. TO PREVENT SCALDING OR INJURY, THE RADIATOR CAP SHOULD NOT BE REMOVED WHILE THE SYS- TEM IS HOT AND/OR UNDER PRESSURE. There is no need to remove the radiator cap ex- cept for the following purposes: • To check and adjust antifreeze freeze point. • To refill system with new antifreeze. • For conducting service procedures. • When checking for vacuum leaks. WARNING: IF VEHICLE HAS BEEN RUN RECENTLY, WAIT AT LEAST 15 MINUTES BEFORE REMOVING RADIATOR CAP. WITH A RAG, SQUEEZE RADIATOR UPPER HOSE TO CHECK IF SYSTEM IS UNDER PRESSURE. PLACE A RAG OVER THE CAP AND WITHOUT PUSHING DOWN, ROTATE CAP COUNTER-CLOCKWISE TO THE FIRST STOP. AL- LOW FLUID TO ESCAPE THROUGH OVERFLOW HOSE INTO COOLANT RESERVE/OVERFLOW TANK. SQUEEZE RADIATOR UPPER HOSE TO DE- TERMINE WHEN PRESSURE HAS BEEN RE- LEASED. WHEN COOLANT AND STEAM STOP BEING PUSHED INTO TANK AND SYSTEM PRES- SURE DROPS, REMOVE RADIATOR CAP COM- PLETELY. Fig. 37 Radiator Pressure Cap—Typical PRESSURE TESTING RADIATOR CAPS Remove cap from radiator. Be sure that sealing A vent valve in the center of the cap allows a small surfaces are clean. Moisten rubber gasket with watercoolant flow through the cap when coolant is below and install the cap on pressure tester (tool 7700 orboiling temperature. The valve is completely closed an equivalent) (Fig. 38).when boiling point is reached. As the coolant cools, it Operate the tester pump and observe the gaugecontracts and creates a vacuum in cooling system. pointer at its highest point. The cap release pressureThis causes the vacuum valve to open and coolant in should be 97-to-124 kPa (14-to-18 psi). The cap isreserve/overflow tank to be drawn through connect- satisfactory when the pressure holds steady. It is alsoing hose into radiator. If the vacuum valve is stuck good if it holds pressure within the 97-to-124 kPashut, radiator hoses will collapse on cool-down. (14-to-18 psi) range for 30 seconds or more. If the A rubber gasket seals the radiator filler neck. This pointer drops quickly, replace the cap.is done to maintain vacuum during coolant cool-downand to prevent leakage when system is under pres- CAUTION: Radiator pressure testing tools are verysure. sensitive to small air leaks, which will not cause cooling system problems. A pressure cap that doesRADIATOR CAP-TO-FILLER NECK SEAL— not have a history of coolant loss should not be re-PRESSURE RELIEF CHECK placed just because it leaks slowly when tested With radiator cap installed on filler neck, remove with this tool. Add water to tool. Turn tool upsidecoolant reserve/overflow tank hose from nipple on down and recheck pressure cap to confirm that capfiller neck. Connect a hand operated vacuum pump needs replacement.to nipple. Operate pump until a reading of 47-to-61kPa (14-to-18 in. Hg) appears on gauge. If the read-ing stays steady, or drops slightly and then remains INSPECTIONsteady, the pressure valve seal is good. Replace radi- Visually inspect the pressure valve gasket on theator cap if reading does not hold. cap. Replace cap if the gasket is swollen, torn or
7 - 30 COOLING SYSTEM SERVICE PROCEDURES ZJ WARNING: CONSTANT TENSION HOSE CLAMPS ARE USED ON MOST COOLING SYSTEM HOSES. WHEN REMOVING OR INSTALLING, USE ONLY TOOLS DESIGNED FOR SERVICING THIS TYPE OF CLAMP, SUCH AS SPECIAL CLAMP TOOL (NUMBER 6094) (FIG. 39). SNAP-ON CLAMP TOOL (NUMBER HPC-20) MAY BE USED FOR LARGER CLAMPS. AL- WAYS WEAR SAFETY GLASSES WHEN SERVICING CONSTANT TENSION CLAMPS. CAUTION: A number or letter is stamped into the tongue of constant tension clamps (Fig. 40). If re- placement is necessary, use only an original equip- ment clamp with matching number or letter. Fig. 38 Pressure Testing Radiator Pressure Cap—Typicalworn. Inspect the area around radiator filler neck forwhite deposits that indicate a leaking cap.RADIATORGENERAL INFORMATION All vehicles are equipped with a cross flow type ra-diator with plastic side tanks. Fig. 39 Hose Clamp Tool—Typical Plastic tanks, while stronger than brass, are sub-ject to damage by impact, such as from tools orwrenches. Handle radiator with care.RADIATOR COOLANT FLOW CHECK The following procedure will determine if coolant isflowing through the cooling system. If engine is cold, idle engine until normal operatingtemperature is reached. Then feel the upper radiatorhose. If hose is hot, the thermostat is open and wateris circulating through cooling system.RADIATOR REMOVALWARNING: DO NOT REMOVE THE CYLINDERBLOCK DRAIN PLUGS OR LOOSEN THE RADIATORDRAINCOCK WITH THE SYSTEM HOT AND UNDERPRESSURE. SERIOUS BURNS FROM COOLANTCAN OCCUR. REFER TO COOLING SYSTEM DRAIN-ING IN THIS GROUP. Do not waste reusable coolant. If the solution isclean, drain the coolant into a clean container for re- Fig. 40 Clamp Number/Letter Locationuse.
ZJ COOLING SYSTEM SERVICE PROCEDURES 7 - 31 Fig. 41 Air Seals—TypicalCAUTION: When removing the radiator or A/C con-denser for any reason, note the location of all radi-ator-to-body and radiator-to-A/C condenser rubberair seals (Fig. 41). These are used at the top, bot-tom and sides of the radiator and A/C condenser.To prevent overheating, these seals must be in-stalled to their original positions. (1) Disconnect the negative battery cable at bat-tery. (2) Observe the previous WARNINGS and CAU-TIONS. (3) Drain coolant from radiator. Refer to DrainingCooling System in this group. (4) 4.0L Engine: Remove the four fan hub-to-wa-ter pump pulley mounting nuts (Fig. 42). Carefullyremove the fan assembly from the water pump pulleyand position to center of fan shroud. Fan belt re-moval is not necessary as the water pump studs willhold the pump pulley in position. Do not remove fan/viscous fan drive assembly fromvehicle at this time. 5.2L Engine: The thermal viscous fan drive is at- Fig. 42 Fan Mounting Nuts—4.0L 6-Cyl. Enginetached (threaded) to the water pump hub shaft (Fig. (number SP346 from Snap-On Cummins Diesel Tool43). Remove fan/viscous fan drive assembly from wa- Set number 2017DSP) can be used. Place a bar orter pump by turning mounting nut counterclockwise screwdriver between water pump pulley bolts (Fig.as viewed from front. Threads on viscous fan driveare RIGHT HAND. A Snap-On 36 MM Fan Wrench