The document discusses cooling system operation and diagnosis. It describes how coolant flows through the engine, thermostat operation, radiator and pressure cap function, and diagnosing cooling system problems. Specifically, it explains that coolant circulates through the engine and radiator to maintain optimal engine temperature, with the thermostat and pressure cap regulating coolant flow and pressure to prevent overheating or low temperature issues.

1. COOLING SYSTEM OPERATION AND DIAGNOSIS 21

2. Objectives The student should be able to: Prepare for ASE Engine Repair (A1) certification test content area “D” (Lubrication and Cooling Systems Diagnosis and Repair). Describe how coolant flows through an engine. Discuss the operation of the thermostat.

3. Objectives The student should be able to: Explain the purpose and function of the radiator pressure cap. Describe the operation and service of water pumps. Discuss how to diagnose cooling system problems.

4. COOLING SYSTEM

5. Cooling System Purpose and Function Cooling system operation depends on design and operating conditions Basis of cooling system design

6. Cooling System Purpose and Function Basis of cooling system design Heat output of engine Radiator size

7. Cooling System Purpose and Function Basis of cooling system design Type of coolant Size of water pump (coolant pump)

8. Cooling System Purpose and Function Basis of cooling system design Type of fan, thermostat, system pressure

9. Cooling System Purpose and Function Cooling system must allow engine to warm up to operating temperature rapidly and then maintain temperature

10. Cooling System Purpose and Function Peak combustion temperature from 4,000°F to 6,000°F (2,200°C to 3,300°C)

11. Cooling System Purpose and Function Average combustion temperatures from 1,200°F to 1,700°F (650°C to 925°C)

12. Cooling System Purpose and Function Continued operation at these temperatures will weaken engine parts Cooling system keeps head and cylinder walls at temperature for maximum efficiency

13. Cooling System Purpose and Function Cooling system removes about one-third of heat One-third of heat escapes through exhaust system

14. Figure 21-1 Typical combustion and exhaust temperatures.

15. Cooling System Low-Temperature Engine Problems Operating temperatures must be above minimum temperature Failure to reach specified temperature may cause engine-related faults

16. Cooling System Low-Temperature Engine Problems PO128 diagnostic trouble code (DTC) Code indicates “coolant temperature below thermostat regulating temperature”

17. Cooling System Low-Temperature Engine Problems Usually a defective thermostat staying open or partly open

18. Cooling System Low-Temperature Engine Problems Moisture created by combustion process Can condense and flow into oil

19. Cooling System Low-Temperature Engine Problems Moisture created by combustion process Each gallon of fuel produces moisture equal to one gallon of water

20. Cooling System Low-Temperature Engine Problems Moisture created by combustion process Condensed moisture combines with unburned hydrocarbons and additives

21. Cooling System Low-Temperature Engine Problems Moisture created by combustion process Forms carbonic acid, sulfuric acid, nitric acid, hydrobromic acid, hydrochloric acid

22. Cooling System Most manufacturers offer block heaters Plug into household current (110 volts AC) Heating element warms coolant

23. Cooling System High-Temperature Engine Problems Maximum engine temperature limits required to protect engine Higher than normal temperatures can cause engine-related issues

24. Cooling System High-Temperature Engine Problems Oxidation of engine oil producing hard carbon and varnish Varnish causes hydraulic valve lifter plungers to stick

25. Cooling System High-Temperature Engine Problems Higher than normal temperatures causes oil to become thinner Thinned oil will cause excessive oil consumption

26. Cooling System High-Temperature Engine Problems High coolant temperatures raise combustion temperature and cause detonation (spark knock or ping)

27. COOLING SYSTEM OPERATION

28. Cooling System Operation Purpose and Function Coolant flows through engine, picks up heat Coolant flows to radiator, heat is passed to outside air

29. Figure 21-2 Coolant circulates through the water jackets in the engine block and cylinder head.

30. Figure 21-3 Coolant flow through a typical engine cooling system.

31. Cooling System Operation Cooling System Operation Coolant temperature rises up to 15°F (8°C) as goes through engine and cools as it goes through radiator

32. Cooling System Operation Cooling System Operation Coolant flow rate may be 1 gallon (4 liters) per minute for each engine horsepower

33. Cooling System Operation Cooling System Operation Hot coolant comes out of thermostat housing on top of engine in most engines

34. Cooling System Operation Cooling System Operation Engine coolant outlet connects to radiator by upper radiator hose and clamps

35. Cooling System Operation Cooling System Operation Coolant is cooled by air flowing through radiator Coolant leaves radiator through outlet and lower radiator hose

36. Cooling System Operation Cooling System Operation Coolant flows to the inlet on water pump, which recirculates it through engine

37. Cooling System Operation Cooling System Operation NOTE: Some newer engine designs place thermostat on inlet side of water pump. Thermostat closes until coolant temperature causes it to open. Placement on inlet side reduces rapid temperature changes.

38. THERMOSTATS

39. Thermostats Purpose and Function Thermostat controls minimum normal temperature Thermostat is temperature-controlled valve place at engine coolant outlet on most engines

40. Thermostats Thermostat Operation Encapsulated wax-based plastic pellet heat sensor on engine side of thermostatic valve Engine heat swells the heat sensor

41. Figure 21-4 A cross section of a typical wax-actuated thermostat showing the position of the wax pellet and spring.

42. Thermostats Thermostat Operation Mechanical link opens thermostat valve Open thermostat allows some coolant to flow to radiator

43. Thermostats Thermostat Operation Remaining coolant flows through bypass to engine Rated temperature of thermostat indicates temperature at which thermostat opens

44. Figure 21-5 (a) When the engine is cold, the coolant flows through the bypass.

45. Figure 21-5 (b) When the thermostat opens, the coolant can flow to the radiator.

46. Thermostats Thermostat Operation Thermostat fully open at about 20°F higher than opening temperature

47. Chart 21-1 The temperature of the coolant depends on the rating of the thermostat.

48. Figure 21-6 A thermostat stuck in the open position caused the engine to operate too cold. If a thermostat is stuck closed, this can cause the engine to overheat.

49. Thermostats Thermostat Operation NOTE: Bypass around closed thermostat allows coolant to circulate during engine warm-up. Bypass may be cast or drilled into engine and pump parts.

50. Figure 21-7 This internal bypass passage in the thermostat housing directs cold coolant to the water pump.

51. Figure 21-8 A cutaway of a small block Chevrolet V-8 showing the passage from the cylinder head through the front of the intake manifold to the thermostat.

52. Thermostats Thermostat Testing Hot Water Method Thermostat is removed and suspended in water using 0.015 in. (0.4mm) feeler gauge with a thermometer

53. Thermostats Thermostat Testing Hot Water Method Container is heated until thermostat opens

54. Thermostats Thermostat Testing Hot Water Method Opening temperature should be within 5°F (4°C) of temperature on thermostat

55. Thermostats Thermostat Testing Infrared Thermometer Method Infrared thermometer (pyrometer) measures temperature near thermostat

56. Thermostats Thermostat Testing Infrared Thermometer Method As engine warms, temperature reaches thermostat opening temperature

57. Thermostats Thermostat Testing Infrared Thermometer Method As thermostat opens, coolant temperature drops

58. Thermostats Thermostat Testing Infrared Thermometer Method As thermostat cycles, temperature ranges from opening temperature to 20°F (11°C) above opening temperature

59. Thermostats Thermostat Testing Infrared Thermometer Method NOTE: If temperature rises more than 20°F (11°C) check for restriction, low coolant flow, clogged radiator

60. Thermostats Scan Tool Method Scan tool reads actual temperature detected by ECT sensor

61. Thermostats Thermostat Replacement Overheating engine may result from faulty thermostat Engine that does not get warm always indicates faulty thermostat

62. Thermostats Thermostat Replacement To replace thermostat, drain coolant from radiator to below level of thermostat

63. Thermostats Thermostat Replacement Remove hose from thermostat housing neck Remove housing to expose thermostat

64. Thermostats Thermostat Replacement Clean gasket flanges and thermostat housing Place thermostat in engine with sensing pellet toward engine

65. Figure 21-10 Some thermostats are an integral part of the housing. This thermostat and radiator hose housing is serviced as an assembly. Some thermostats snap into the engine radiator fill tube underneath the pressure cap.

66. Thermostats Thermostat Replacement Install thermostat housing with new gasket or O-ring CAUTION: Failure to set thermostat into recessed groove will cause housing to tilt.

67. Thermostats Thermostat Replacement Tightening bolts will usually crack housing, creating leak

68. RADIATORS

69. Radiators Types Serpentine fin core Plate fin core

70. Radiators Types In each type, coolant flows through oval-shaped core tubes Heat is transferred to cooling fins

71. Radiators Types Air flows through radiator and removes heat Older radiators made from yellow brass

72. Figure 21-11 The tubes and fins of the radiator core.

73. Figure 21-12 (a) A radiator may be either a down-flow or a crossflow type.

74. Figure 21-12 (b) A radiator may be either a down-flow or a crossflow type.

75. Radiators Types Since 1980s, radiators made from aluminum with nylon-reinforced plastic side tanks

76. Radiators Types Core tubes are 0.0045 to 0.012 in. (0.1 to 0.3 mm) sheet brass or aluminum

77. Radiators Types Two Basic Designs: Down-flow radiators Cross-flow radiators

78. Radiators How Radiators Work Main limitation of heat transfer is from radiator to the air Heat transfers from water to fins up to seven times faster than from fins to air

79. Radiators How Radiators Work Radiator must remove heat equal to heat energy produced by engine Each horsepower equals 42 BTUs (10,800 calories) per minute

80. Radiators How Radiators Work Radiator capacity by be increased by increasing core thickness or packing more material in same volume, or both

81. Radiators How Radiators Work NOTE: Lower air dam in front of vehicle directs air through radiator. Damaged or missing air dam can cause engine to overheat.

82. Radiators How Radiators Work When transmission oil cooler is used, it is placed in outlet tank

83. Figure 21-13 Many vehicles equipped with an automatic transmission use a transmission fluid cooler installed in one of the radiator tanks.

84. PRESSURE CAPS

85. Pressure Caps Operation Cap has spring-loaded valve that closes cooling system vent Cooling pressure builds up to pressure setting of cap

86. Pressure Caps Operation Cap releases excess pressure Pressure raises boiling temperature of coolant Boiling temperature increases about 3°F (1.6°C) per pound of pressure

87. Pressure Caps Operation Pressure raises boiling temperature of coolant At sea level, water boils at 212°F (100°C)

88. Pressure Caps Operation Pressure raises boiling temperature of coolant 15 PSI (100kPa) pressure cap increases boiling temp to 257°F (125°C)

89. Pressure Caps Functions Specified coolant system temperature serves two purposes: Allows engine to run at efficient temperature, close to 200°F (93°C)

90. Pressure Caps Functions Specified coolant system temperature serves two purposes: The higher the coolant temperature, the more heat it can transfer

91. Pressure Caps Functions Specified coolant system temperature serves two purposes: For proper cooling, system must have right pressure cap

92. Pressure Caps Functions Vacuum valve allows coolant to flow back to radiator when it cools down NOTE: Proper pressure cap especially important at high altitudes.

93. Figure 21-14 The pressure valve maintains the system pressure and allows excess pressure to vent. The vacuum valve allows coolant to return to the system from the recovery tank.

94. Pressure Caps Functions NOTE: Proper pressure cap especially important at high altitudes. Boiling point of water lowered by about 1°F for every 550 ft increase in altitude

95. Pressure Caps Functions NOTE: Proper pressure cap especially important at high altitudes. In Denver, Colorado (altitude 5,280 ft), water boils at 202°F

96. Pressure Caps Metric Radiator Caps All radiator caps indicate their normal pressure rating Most original equipment radiator caps rated at 14 to 16 PSI (97 to 110kPa)

97. Pressure Caps Metric Radiator Caps Many vehicles from Japan and Europe measure pressure in unit called bar One bar is about 14.7 PSI

98. Chart 21-2 Comparison showing the metric pressure as shown on the top of the cap to pounds per square inch (PSI).

99. Pressure Caps Metric Radiator Caps NOTE: Many radiator repair shops use 7PSI (0.5bar) radiator caps. A 7 PSI cap provides boil protection of 21°F (3°F × 7 PSI = 21°F) above boiling point

100. Pressure Caps Metric Radiator Caps NOTE: Many radiator repair shops use 7PSI (0.5bar) radiator caps. The coolant can still boil before the “hot” dash warning light comes on

101. Pressure Caps Metric Radiator Caps NOTE: Many radiator repair shops use 7PSI (0.5bar) radiator caps. Lower boil point can cause cavitation and damage water pump

102. Pressure Caps Metric Radiator Caps NOTE: Many radiator repair shops use 7PSI (0.5bar) radiator caps. Always follow vehicle manufacturer’s recommended radiator cap

103. COOLANT RECOVERY SYSTEMS

104. Coolant Recovery Systems Purpose and Function Excess pressure causes coolant to overflow Most cooling systems connect to plastic reservoir to hold excess coolant

105. Figure 21-15 The level in the coolant recovery system raises and lowers with engine temperature.

106. Coolant Recovery Systems Purpose and Function When system cools, pressure is reduced creating partial vacuum Vacuum pulls coolant from reservoir back into cooling system

107. Coolant Recovery Systems Purpose and Function System called coolant recovery system

108. Coolant Recovery Systems Surge Tank Some vehicles use surge tank Surge tank located at highest level of cooling system

109. Coolant Recovery Systems Surge Tank Surge tank holds about 1 quart (1 liter) of coolant Hose attaches bottom of surge tank to inlet side of water pump

110. Coolant Recovery Systems Surge Tank Smaller bleed hose attaches side of surge tank to highest point of radiator Bleed line allows some coolant circulation through surge tank

111. Coolant Recovery Systems Surge Tank Air is forced from system if pressure exceeds rating of radiator cap

112. Figure 21-16 Some vehicles use a surge tank, which is located at the highest level of the cooling system, with a radiator cap.

113. WATER PUMPS

114. Water Pumps Operation Water pump is driven by one of two methods: Crankshaft belt Camshaft

115. Water Pumps Operation Coolant recirculates from radiator to engine and back to radiator Low-temperature coolant leaves radiator by bottom outlet

116. Water Pumps Operation Coolant flows to engine block and then to cylinder heads NOTE: Some engines use reverse-cooling. Coolant flows from radiator to cylinder heads before flowing to engine block.

117. Water Pumps Operation Water pump is not positive displacement pump Water pump is centrifugal pump

118. Water Pumps Operation Pump pulls coolant in at the center of the impeller Centrifugal force throws coolant outward to be discharged at impeller tips ?

119. Figure 21-17 Coolant flow through the impeller and scroll of a coolant pump for a V-type engine.

120. Water Pumps Operation Higher engine speeds produce more heat Pump impeller speed increases with engine speed

121. Water Pumps Operation Coolant leaving pump impeller feeds through a scroll Scroll connects to front of engine to direct coolant into engine block

122. Water Pumps Operation On V-type engines, two outlets are often used Occasionally, diverts are needed to equalize coolant flow between engine banks

123. Water Pumps Water Pump Service Worn impeller can reduce amount of coolant flow If water pump seal fails, coolant will leak from weep hole

124. Figure 21-19 This severely corroded water pump could not circulate enough coolant to keep the engine cool. As a result, the engine overheated and blew a head gasket.

125. Water Pumps Water Pump Service Weep hole allows coolant to escape Defective bearing is noisy and must be replaced

126. Figure 21-20 The bleed weep hole in the water pump allows coolant to leak out of the pump and not be forced into the bearing. If the bearing failed, more serious damage could result.

127. Water Pumps Water Pump Service Before replacing water pump because of noisy bearing, check Drive belt tension Bent fan

128. Water Pumps Water Pump Service Before replacing water pump because of noisy bearing, check Fan for balance

129. Water Pumps Water Pump Service If pump drive belt is too tight, excessive force may be exerted on pump bearing

130. Water Pumps Water Pump Service If cooling fan is bent or out of balance, vibration can damage pump bearing

131. Figure 21-21 A cutaway of a typical water pump showing the long bearing assembly and the seal. The weep hole is located between the seal and the bearing. If the seal fails, then coolant flows out of the weep hole to prevent the coolant from damaging the bearing.

132. COOLANT FLOW IN THE ENGINE

133. Coolant Flow in the Engine Types of Systems Coolant flows through engine in one of following ways Parallel flow system Coolant flows into block under pressure and then crosses the head gasket to the head through main coolant passages beside each cylinder

134. Coolant Flow in the Engine Types of Systems Coolant flows through engine in one of following ways Series flow system Coolant flows around cylinders on each bank

135. Coolant Flow in the Engine Types of Systems Coolant flows through engine in one of following ways Series flow system Coolant flows to rear of block where coolant flows across head gasket

136. Coolant Flow in the Engine Types of Systems Coolant flows through engine in one of following ways Series flow system Coolant then enters rear of heads

137. Coolant Flow in the Engine Types of Systems Coolant flows through engine in one of following ways Series flow system In heads, coolant flows forward to crossover passage on intake manifold outlet at highest point in engine cooling passage

138. Coolant Flow in the Engine Types of Systems Coolant flows through engine in one of following ways Series-parallel flow system Combination of series-flow and parallel-flow systems

139. Coolant Flow in the Engine Types of Systems Coolant flows through engine in one of following ways Series-parallel flow system Any stem goes directly to top of radiator

140. Coolant Flow in the Engine Types of Systems Coolant flows through engine in one of following ways Series-parallel flow system Bleed holes or steam slits let out the steam

141. Coolant Flow in the Engine Coolant Flow and Head Gasket Design Most but not all V-type engines use cylinder heads that are interchangeable side to side

142. Coolant Flow in the Engine Coolant Flow and Head Gasket Design Double check that cylinder head is matched to block and that head gasket is installed correctly

143. Figure 21-22 A Chevrolet V-8 block that shows the large coolant holes and the smaller gas vent or bleed holes that must match the head gasket when the engine is assembled.

144. COOLING FANS

145. Cooling Fans Electronically Controlled Cooling Fan Two Types One two-speed cooling fan

146. Cooling Fans Electronically Controlled Cooling Fan Two Types Two cooling fans (one for normal cooling; one for high heat conditions)

147. Cooling Fans Electronically Controlled Cooling Fan PCM commands low-speed fans under these conditions ECT exceeds approximately 223°F (106°C)

148. Cooling Fans Electronically Controlled Cooling Fan PCM commands low-speed fans under these conditions A/C refrigerant pressure exceeds 190 PSI (1,310 kPa)

149. Cooling Fans Electronically Controlled Cooling Fan PCM commands low-speed fans under these conditions After engine is shut off, coolant temperature is greater than 284°F (140°C) and system voltage is more than 12 volts.

150. Cooling Fans Electronically Controlled Cooling Fan PCM commands the high-speed fan under these conditions ECT reaches 230°F (110°C)

151. Cooling Fans Electronically Controlled Cooling Fan PCM commands the high-speed fan under these conditions A/C refrigerant pressure exceeds 240 PSI (1,655 kPa)

152. Cooling Fans Electronically Controlled Cooling Fan PCM commands the high-speed fan under these conditions Certain DTCs set

153. Cooling Fans Electronically Controlled Cooling Fan To prevent excessive fan cycling, fan may not turn off until ignition is turned off or vehicle speed exceeds 10 mph (16km/h)

154. Cooling Fans Electronically Controlled Cooling Fan Many rear-wheel-drive vehicles and all transverse engines drive the fan with an electric motor

155. Figure 21-23 A typical electric cooling fan assembly showing the radiator and related components.

156. Cooling Fans Electronically Controlled Cooling Fan NOTE: Most electric cooling fans are computer controlled. Most are turned off when vehicle exceeds 35 mph (55 km/h). Ram air keeps radiator cool. If computer senses temperature is too high, computer turns on cooling fan.

157. Cooling Fans Thermostatic Fans On some rear-wheel-drive vehicles, a thermostatic cooling fan is driven by a belt from the crankshaft

158. Cooling Fans Thermostatic Fans The cooling systems transfers more heat at higher speeds

159. Cooling Fans Thermostatic Fans Two Types of Thermostatic Fans: Silicone coupling: fan drive is mounted between drive pulley and fan HINT: When diagnosing overheating, examine cooling fan. If silicone is leaking, fan may not function correctly.

160. Cooling Fans Thermostatic Fans Two Types of Thermostatic Fans: Thermostatic spring: thermostatic spring added to silicone coupling fan drive Thermostatic spring operates valve that allows fan to freewheel when radiator is cold

161. Cooling Fans Thermostatic Fans Two Types of Thermostatic Fans: Thermostatic spring: thermostatic spring added to silicone coupling fan drive When radiator warms to 150°F (65°C), spring opens valve that allows drive to operate like silicone coupling drive

162. Figure 21-24 A typical engine-driven thermostatic spring cooling fan.

163. HEATER CORES

164. Heater Cores Purpose and Function Some heat absorbed by cooling system passes through tubes to small core of the heater

165. Heater Cores Purpose and Function Air passes across heater fends and sent to passenger compartment

166. Figure 21-25 A typical heater core installed in a heating, ventilation, and air-conditioning (HVAC) housing assembly.

167. Heater Cores Heater Problem Diagnosis To find cause of lack of heat to heater follow these steps

168. Heater Cores Heater Problem Diagnosis Step 1: Feel upper radiator hose; it should be too hot to hold; it should have pressure. If hose is not hot, replace thermostat.

169. Heater Cores Heater Problem Diagnosis Step 1: Feel upper radiator hose; it should be too hot to hold; it should have pressure. If hose is not pressurized, test or replace radiator pressure cap.

170. Heater Cores Heater Problem Diagnosis Step 1: Feel upper radiator hose; it should be too hot to hold; it should have pressure. If okay, see step 2.

171. Heater Cores Heater Problem Diagnosis Step 2: With engine running, feel both heater hoses. Both should be too hot to hold. If hoses are warm or cool, check heater control valve.

172. Heater Cores Heater Problem Diagnosis Step 2: With engine running, feel both heater hoses. Both should be too hot to hold. If one hose is hot and other warm or cool, remove hoses and flush heater core.

173. Heater Cores Heater Problem Diagnosis Step 3: If both hoses are hot but heat is insufficient, check for airflow blend door malfunction.

174. Heater Cores HINT: Heat from heater that comes and goes is likely the result of low coolant level. It may work at lower engine speeds but not at higher speeds.

175. COOLING SYSTEM TESTING

176. Cooling System Testing Visual Inspection Many faults can be identified with visual inspection Water pump drive belt for tension or faults

177. Cooling System Testing Visual Inspection Many faults can be identified with visual inspection Cooling fan for faults

178. Cooling System Testing Visual Inspection Many faults can be identified with visual inspection Heater and radiator hoses for condition and leaks

179. Cooling System Testing Visual Inspection Many faults can be identified with visual inspection Coolant overflow or surge tank coolant level

180. Cooling System Testing Visual Inspection Many faults can be identified with visual inspection Evidence of coolant loss

181. Cooling System Testing Visual Inspection Many faults can be identified with visual inspection Radiator condition

182. Figure 21-26 A heavily corroded radiator from a vehicle that was overheating. A visual inspection discovered that the corrosion had eaten away many of the cooling fins, yet did not leak. This radiator was replaced and it solved the overheating problem.

183. Cooling System Testing Pressure Testing Using hand-operated pressure tester, remove radiator cap Operating plunger on pump pressurizes cooling system

184. Figure 21-27 Pressure testing the cooling system. A typical handoperated pressure tester applies pressure equal to the radiator cap pressure. The pressure should hold; if it drops, this indicates a leak somewhere in the cooling system. An adapter is used to attach the pump to the cap to determine if the radiator can hold pressure, and release it when pressure rises above its maximum rated pressure setting.

185. Cooling System Testing Pressure Testing CAUTION: Do not pump up pressure beyond that specified by vehicle manufacturer, usually 14 PSI (100 kPa).

186. Cooling System Testing Pressure Testing If system is free from leaks, pressure will stay and not drop

187. Cooling System Testing Pressure Testing If pressure drops check for leaks Heater hoses Radiator hoses

188. Cooling System Testing Pressure Testing If pressure drops check for leaks Radiator Heater core

189. Cooling System Testing Pressure Testing If pressure drops check for leaks Cylinder head Core plugs in block or cylinder head

190. Cooling System Testing Pressure Testing Perform pressure testing whenever there is leak or suspected leak Pressure tester can also be used to test radiator cap

191. Figure 21-28 The pressure cap should be checked for proper operation using a pressure tester as part of the cooling system diagnosis.

192. Cooling System Testing Coolant Dye Leak Testing Use fluorescent dye in coolant Operate vehicle to reach normal operating temperature

193. Cooling System Testing Coolant Dye Leak Testing Use black light to inspect cooling system

194. Figure 21-29 Use dye specifically made for coolant when checking for leaks using a black light.

195. COOLANT TEMPERATURE WARNING LIGHT

196. Coolant Temperature Warning Light Purpose and Function Most vehicles have heat sensor to engine operating temperature indicator light

197. Coolant Temperature Warning Light Purpose and Function If light comes on (or temperature gauge goes into red danger zone) coolant is 250°F to 258°F (120°C to 126°C)

198. Figure 21-30 When an engine overheats, often the coolant overflow container boils.

199. Coolant Temperature Warning Light Precautions If coolant temperature warning light comes on, follow these steps Step 1: Shut off air conditioning and turn on heater. Set blower speed to high.

200. Coolant Temperature Warning Light Precautions If coolant temperature warning light comes on, follow these steps Step 2: Shut engine off and let it cool. Step 3: Do not remove radiator cap while engine is hot.

201. Coolant Temperature Warning Light Precautions If coolant temperature warning light comes on, follow these steps Step 4: Do not continue to drive. Step 5: If engine does not feel or smell hot, problem may be faulty hot light sensor or gauge.

202. Coolant Temperature Warning Light Common Causes of Overheating Low coolant level Plugged, dirty, or blocked radiator

203. Coolant Temperature Warning Light Common Causes of Overheating Defective fan clutch or electric fan Incorrect ignition timing (if adjustable)

204. Coolant Temperature Warning Light Common Causes of Overheating Low engine oil level Broken fan drive belt

205. Coolant Temperature Warning Light Common Causes of Overheating Defective radiator cap Dragging brakes

206. Coolant Temperature Warning Light Common Causes of Overheating Frozen coolant (in freezing weather) Defective thermostat

207. Coolant Temperature Warning Light Common Causes of Overheating Defective water pump (impeller slipping on internal shaft) Blocked cooling passages in block or cylinder head(s)

208. COOLING SYSTEM INSPECTION

209. Cooling System Inspection Coolant Level Normal maintenance involves checking coolant level and visual inspection for leaks and condition of hoses and belts

210. Cooling System Inspection Coolant Level CAUTION: Check coolant only when engine is cool. Removing pressure cap from hot engine will cause coolant to boil immediately. Vapors will blow coolant from system. Coolant will be lost; someone may be injured.

211. Cooling System Inspection Accessory Drive Belt Tension Four ways manufacturers specific belt tension is within specifications Belt tension gauge Install belt and operate engine for five minutes

212. Cooling System Inspection Accessory Drive Belt Tension Four ways manufacturers specific belt tension is within specifications Belt tension gauge Adjust tension to factory specifications or use Chart 21-3

213. Chart 21-3 The number of ribs determines the tension range of the belt.

214. Cooling System Inspection Accessory Drive Belt Tension Four ways manufacturers specific belt tension is within specifications Belt tension gauge Replace serpentine belt with more than three cracks in 3 in. span

215. Cooling System Inspection Accessory Drive Belt Tension Four ways manufacturers specific belt tension is within specifications Marks on tensioner Many tensioners have marks indicating normal operating tension range

216. Cooling System Inspection Accessory Drive Belt Tension Four ways manufacturers specific belt tension is within specifications Marks on tensioner Check service information for location of tensioner mark

217. Figure 21-31 Typical marks on an accessory drive belt tensioner.

218. Cooling System Inspection Accessory Drive Belt Tension Four ways manufacturers specific belt tension is within specifications Torque wrench reading Some manufacturers specify use of beam-type torque wrench

219. Cooling System Inspection Accessory Drive Belt Tension Four ways manufacturers specific belt tension is within specifications Deflection Depress belt between the two pulleys that are farthest apart

220. Cooling System Inspection Accessory Drive Belt Tension Four ways manufacturers specific belt tension is within specifications Deflection Deflection should be 1/2 in.

221. COOLING SYSTEM SERVICE

222. Cooling System Service Flushing Coolant Step 1: Drain system. Step 2: Fill system with clean water and flushing/cleaning chemical.

223. Cooling System Service Flushing Coolant Step 3: Start engine; run until it reaches operating temperature with heater on. Step 4: Drain system and fill with water.

224. Cooling System Service Flushing Coolant Step 5: Repeat until drain water runs clear. Step 6: Fill system with 50/50 antifreeze/water mix or premixed coolant.

225. Cooling System Service Flushing Coolant Step 7: Run engine until it reaches operating temperature with heater on. Step 8: Adjust coolant level as needed.

226. Cooling System Service Flushing Coolant Bleed air from cooling system Attach clear hose to bleeder valve; put other end in container

227. Cooling System Service Flushing Coolant Bleed air from cooling system Check service information for specific bleeding procedures and location of bleeder fittings

228. Figure 21-32 (a) Many vehicle manufacturers recommend that the bleeder valve be opened whenever refilling the cooling system.

229. Figure 21-32 (b) Chrysler recommends that a clear plastic hose (1/4 in. ID) be attached to the bleeder valve and directed into a suitable container to keep from spilling coolant onto the ground and on the engine and to allow the technician to observe the flow of coolant for any remaining oil bubbles.

230. Cooling System Service Coolant Exchange Machine Many coolant exchange machines can perform one of more of these operations Exchange old coolant with new coolant

231. Cooling System Service Coolant Exchange Machine Many coolant exchange machines can perform one of more of these operations Flush cooling system

232. Cooling System Service Coolant Exchange Machine Many coolant exchange machines can perform one of more of these operations Pressure or vacuum check system for leaks

233. Cooling System Service Coolant Exchange Machine Exchange machine helps eliminate air pockets

234. Cooling System Service Coolant Exchange Machine Air pockets show these symptoms Lack of heat from heater

235. Cooling System Service Coolant Exchange Machine Air pockets show these symptoms Overheating

236. Figure 21-33 Using a coolant exchange machine helps eliminate the problem of air getting into the system which can cause overheating or lack of heat due to air pockets getting trapped in the system.

237. Cooling System Service Hose Inspection A hose should be replaced any time it appears abnormal

238. Figure 21-34 All cooling system hoses should be checked for wear or damage.

239. Cooling System Service Hose Inspection HINT: To make hose removal easier and to avoid damage to radiator, slit hose lengthwise with utility knife. Peel hose off.

240. Cooling System Service Hose Inspection Position hose and hose clam so clamp is close to the bead on the neck

241. Cooling System Service Disposing of Used Coolant Dispose of coolant according to state or local laws Some communities allow draining into sewer

242. Cooling System Service Disposing of Used Coolant Groundwater contamination can occur if coolant is spilled on ground Check with recycling companies for recommended disposal methods

243. Cooling System Service Cleaning the Radiator Exterior Overheating can result from exterior and interior radiator plugging

244. Cooling System Service Cleaning the Radiator Exterior Exterior plugging can be seen if you look through the radiator Exterior can be cleaned with water pressure from hose

245. TECH TIP Overheating Can Be Expensive A faulty cooling system seems to be a major cause of engine failure. Engine rebuilders often have nightmares about seeing their rebuilt engine placed back in service in a vehicle with a clogged radiator. BACK TO PRESENTATION Most engine technicians routinely replace the water pump and all hoses after an engine overhaul or repair. The radiator should also be checked for leaks and proper flow whenever the engine is repaired or replaced. Overheating is one of the most common causes of engine failure.

246. TECH TIP Do Not Take Out the Thermostat! Some vehicle owners and technicians remove the thermostat in the cooling system to “cure” an overheating problem. In some cases, removing the thermostat can cause overheating rather than stop it. This is true for three reasons. BACK TO PRESENTATION Without a thermostat the coolant can flow more quickly through the radiator. The thermostat adds some restriction to the coolant flow, and therefore keeps the coolant in the radiator longer. This also allows additional time for the heat transfer between the hot engine parts and the coolant. The presence of the thermostat thus ensures a greater reduction in the coolant temperature before it returns to the engine. Heat transfer is greater with a greater difference between the coolant temperature and air temperature. Therefore, when coolant flow rate is increased (no thermostat), the temperature difference is reduced Without the restriction of the thermostat, much of the coolant flow often bypasses the radiator entirely and returns directly to the engine. If overheating is a problem, removing the thermostat will usually not solve the problem. Remember, the thermostat controls the temperature of the engine coolant by opening at a certain temperature and closing when the temperature falls below the minimum rated temperature of the thermostat.

247. TECH TIP Working Better Under Pressure A problem that sometimes occurs with a high-pressure cooling system involves the water pump. For the pump to function, the inlet side of the pump must have a lower pressure than its outlet side. If inlet pressure is lowered too much, the coolant at the pump inlet can boil, producing vapor. BACK TO PRESENTATION The pump will then spin the coolant vapors and not pump coolant. This condition is called pump cavitation. Therefore, a radiator cap could be the cause of an overheating problem. A pump will not pump enough coolant if not kept under the proper pressure for preventing vaporization of the coolant.

248. REAL WORLD FIX The Collapsed Radiator Hose Story An automotive student asked the automotive instructor what brand of radiator hose is the best. Not knowing exactly what to say, the instructor asked if there was a problem with the brand hose used. The student had tried three brands and all of them collapsed when the engine cooled. BACK TO PRESENTATION The instructor then explained that the vehicle needed a new pressure cap and not a new upper radiator hose. The student thought that because the lower hose did not collapse that the problem had to be a fault with the hose. The instructor then explained that the lower radiator hose has a spring inside to keep the lower hose from collapsing due to the lower pressure created at the inlet to the water pump. The radiator cap was replaced and the upper radiator hose did not collapse when the engine cooled.

249. FREQUENTLY ASKED QUESTION How Much Coolant Can a Water Pump Move? A typical water pump can move a maximum of about 7,500 gallons (28,000 liters) of coolant per hour, or recirculate the coolant in the engine over 20 times per minute. ? BACK TO PRESENTATION This means that a water pump could be used to empty a typical private swimming pool in an hour! The slower the engine speed, the less power is consumed by the water pump. However, even at 35 mph (56 km/h), the typical water pump still moves about 2,000 gallons (7,500 liters) per hour or 0.5 gallon (2 liters) per second! Figure 21-18 A demonstration engine running on a stand, showing the amount of coolant flow that actually occurs through the cooling system.

250. TECH TIP Release the Belt Tension Before Checking a Water Pump The technician should release water pump belt tension before checking for water pump bearing looseness. To test a water pump bearing, it is normal to check the fan for movement; however, if the drive belt is tight, any looseness in the bearing will not be felt. BACK TO PRESENTATION

251. WARNING Some electric cooling fans can come on after the engine is off without warning. Always keep hands and fingers away from the cooling fan blades unless the electrical connector has been disconnected to prevent the fan from coming on. Always follow all warnings and cautions. BACK TO PRESENTATION

252. REAL WORLD FIX Highway Overheating A vehicle owner complained of an overheating vehicle, but the problem occurred only while driving at highway speeds. The vehicle, equipped with a 4-cylinder engine, would run in a perfectly normal manner in city driving situations. BACK TO PRESENTATION The technician flushed the cooling system and replaced the radiator cap and the water pump, thinking that restricted coolant flow was the cause of the problem. Further testing revealed coolant spray out of one cylinder when the engine was turned over by the starter with the spark plugs removed. A new head gasket solved the problem. Obviously, the head gasket leak was not great enough to cause any problems until the engine speed and load created enough flow and heat to cause the coolant temperature to soar. The technician also replaced the oxygen (O 2 ) sensor, because the IAT-type coolant contains phosphates and silicates that often contaminate the sensor. The deteriorated oxygen sensor could have contributed to the problem.

253. TECH TIP The Water Spray Trick Lower-than-normal alternator output could be the result of a loose or slipping drive belt. All belts (V and serpentine multigroove) use an interference angle between the angle of the Vs of the belt and the angle of the Vs on the pulley. A belt wears this interference angle off the edges of the V of the belt. BACK TO PRESENTATION As a result, the belt may start to slip and make a squealing sound even if tensioned properly. A common trick to determine if the noise is from the belt is to spray water from a squirt bottle at the belt with the engine running. If the noise stops, the belt is the cause of the noise. The water quickly evaporates and therefore, water just finds the problem—it does not provide a short-term fix.

254. TECH TIP Always Replace the Pressure Cap Replace the old radiator cap with a new cap with the same pressure rating. The cap can be located on the following: Radiator Coolant recovery reservoir Upper radiator hose BACK TO PRESENTATION

255. WARNING Never remove a pressure cap from a hot engine. When the pressure is removed from the system, the coolant will immediately boil and will expand upward, throwing scalding coolant in all directions. Hot coolant can cause serious burns. BACK TO PRESENTATION