Introduction to lub and cooling sys

INTRODUCTION TO LUBRICATION SYSTEM
The purpose of the lubrication is as follows:
1) To reducefriction between the moving parts.
2) To reducewear of the mating parts.
3) To act as a cooling medium for removing heat.
4) To keep the engine partsclean, especially piston ring & ring grooves, oil
ways and filter. During the circulation, lubricantdissolves many impurities.
5) It provides cushioning effectby absorbing shocksbetween bearing and
the other engine partsthus reducing engine noise and extending engine life.
6) To form a good seal between piston ring and cylinder wall.
7) To prevent deposition of carbon.
8) It prevents corrosion of the metallic components.
The functions of the lubricating oil in an engine are as follows;
1) To minimise friction and wear between mating parts.
2) To cool the engine by carrythe heat away.
3) To seal the gap between piston ring and cylinder liner walls & thus
prevent escape of gases from cylinder (i.e.: Minimise blow-by).
4) To cushion the partsagainst vibration and impact.
5) To clean the parts along with lubrication. Thus carryaway the impurities.
PROPERTIES OF ENGINE LUBRICATION OIL:
Engine lubrication oil must have certain propertiesor characteristic for its
satisfactory functioning. Theyare as follows;
1)Viscosity:

It is propertyof the lubricating oil that offersresistance to flow.
• It is propertydue to which 2 bearing surfacearekept apart.
• The viscosity of lubricantshould be sufficient to ensure hydrodynamic
lubrication. If it is morethan required value, it will cause higher power loss due
to increased oil resistance.
• Viscosity is inversely proportional to temperature. Viscositydecreases
with rise in temperature& increases with fallof temperature.
• Viscosity Index (VI) isan indication of changeof viscosity with respect to
temperature. Higher viscosity index means less changeof oil viscosity with
respect to rise in temperature.
• Most lubrication oils are selected on the basis of the viscosity and
viscosity index.
2)Flash point:
Flash pointis defined as the lowest temperatureat which the lubricating oil will
flash when a small flame is passed across its surface.
Flash pointof oil should be sufficiently high so as to avoid flashing of oil vapors
at the temperatureoccurring in common use.
3)Resistance to corrosion:
The oil should not have tendency to corrodethe pipe lines, crankcaseand other
engine partswith which it comes in contact.
4)Physicalstability:
The lubricating oil must be stable physically at the lowest and the highest
temperatureencountered. Itshould not vaporize at high temperatureand there
should not be separation of solids at lower temperature.
5)Pour Point:
The lowest temperatureat which lubricating oil will pour. It is ability of
lubricating oil to flow at lowest temperature.
6)Adhesiveness:

It is propertyof lubricating oil due to which the oil particles stick with the metal
surface.
7)Chemicalstability:
Lubricating oil should be chemically stable. It should not have tendency of oxide
formation. Theoil should notdecompose at high temperatureto form carbon.
8)Cleanliness:
The oil should be sufficiently clean and stable, so that the crankoil holes and oil
lines arekept clean.
It containsagents, called detergents. These detergents remove the impurities
from engine partsduring oil circulation. These impurities may either be filtered
out or removed with changeof oil at periodic intervals.
9)Resistance against extreme pressure:
In modern engines, lubricating oil are subjected to extreme pressure,
particularlyin bearingsand the valve actuating mechanisms.
The oil must stick to metal surfaceeven under high pressureto reduce the
friction between mating parts.
ADDITIVES FOR LUBRICANTS:
Additives are chemical substances which areadded to the lubricating oil either
to reinforcesome of its naturalpropertiesor to provideit certain new
propertieswhich it does notpossesses originally.
Oil additives are classified as follows;
1. Viscosity index improvers
2. Oxidation Inhibitors
3. Corrosion inhibitors
4. Detergents and Dispersants
5. Anti-scuffing additives

6. Anti-foaming additives
7. Extreme Pressureadditives
8. Pour pointdepressants
9. Rust inhibitors
1.Viscosityindex improver:
These arethe additives which minimise or resist the decrease of oil viscosity
with the increasein temperature.
The additives areusually polymers such as acriloid plastics. These are long chain
molecules, on heating the molecule unwind and prevent movement of the
hydrocarbon molecules. Thusoil viscosity does notdecrease with temperature.
2.Oxidation Inhibitors:
At high temperatureoil in the crankcasereacts with air, the oil oxidation takes
place. This oxidized oil formsvarious harmful substances. These are extremely
sticky tar like substances. They may clog oil channelsand restrict the action of
piston ring and valve. Oxidation inhibitors prevent formation of such harmful
substances.
3.Corrosion inhibitors:
Corrosion inhibitorsprevent the formation of acids which could cause bearing
corrosion.
4.Detergentsand Dispersants:
Additives which handlehigh temperaturedeposits are called “detergents” &
additives which deal with low temperaturedeposits are called “dispersants”.
Dispersantsprevent clotting of oil. Without dispersant, the small particles will
form largeparticles which might block the oil filter and oil passages.

5.Anti-scuffing additives:
This additive help to polish mating partssuch as piston, cylinder wall, cams etc.
and there by preventtheir tendency of scuffing.
6.Anti-foaming additives:
The engine oil may have tendency to form foam dueto enginevibration, which
causes churning of oil in the sump. Heat and churning mixtureproducefoam.
This foam decreases lubricating propertiesof the oil.
Thus anti foaming additives are added which suppressthe foaming tendency of
lubricating oil.
7.ExtremePressureadditives:
At high pressure and temperature, the oil film between moving parts is likely to
break down and allow metal to metal contact. Thus causing wear of the mating
parts.
These additives provideextra film strength by forming a chemical film and
reducethe wear of mating parts.
8.Pour pointdepressants:
These serve to lower the pour point of the oil by coating the wax crystals in the
oil so that they would not stick together and facilitate the oil flow.
9.Rustinhibitors:
Rust inhibitorsare added which displaces water from metal surface so that oil
coats them.
ENGINE PARTS TO BE LUBRICATED:
The engine parts which need to be lubricated are as follows;

1. Main crankshaftbearings
2. Big end bearings
3. Small end bearings
4. Camshaftbearings
5. Piston ringsand cylinder walls
6. Timing gear
7. Valve mechanism
TYPES OF LUBRICATION SYSTEM
The various systems adopted for the lubrication of automobileengine are;
1. PetroilSystem
2. Splash System
3. PressureSystem
4. DrySump System
5. Wet Sump System
1. PETROIL SYSTEM:
The features of this Petroilsystem are as follows;
• This system is used for small 2 stroke engines e.g. in scooter & motor
cycle engines. It is the simplest type of engine lubrication systems.
• Certain amountof lubricating oil is mixed with the petrol itself, the usual
ratio being 2 – 3%.
• If the lubricating oil is less, there is danger of oil starvation. The
insufficientlubrication casing damageto the engine.
• If the lubrication oil is more, there will be excessive carbon deposits in
the cylinder head & the engine will also emit black smoke.

• When the petrolmixture enters the crankcase, due to high temperature
there, the petrolcomponentvaporizes leaving thin film of lubricating oil on the
crankcase, cylinder walls, crankshaft& bearings.
• The main requirementof the lubricating oil for 2 stroke engine is; it
should mix with petrol& burn withoutleaving residue.
2. SPLASH SYSTEM:
The features of this Splash system are as follows;
• This system is employed in the engines of the motor cycles. It’sthe
cheapest method of engine lubrication.
• The lubricating oil is stored in an oil trough or sump.
• A scoop or a dipper is made in the lowest partof the connecting rod.
• When the engine runs, the scoop causes the oil to splash each time it
passes through its B.D.C. position.
• This affects the lubrication of engine walls, gudgeon bearings, big end
bearingsetc.

3. Pressure System:
The features of this Pressuresystem are as follows;
• This system is most widely used system in modern cars.
• In this system, the engine partsare lubricated under pressurefeed. The oil
pump takes the oil from the wet sump through a filter to main oil gallery at a
pressure of 200 – 400 kPa.
• The oil from main gallery goes to the main bearing, some lubricantfallbacks
to the sump & some is splashed to lubricatecylinder walls.
• From crankpin it goes to the piston pin through a hole in the connecting rod.

• Lubrication of camshaftand timing gear is gone through separateoil lines
from the oil gallery.
• Sometimes rocker armsare mounted on the hollow shaft, which carryoil
under pressure. The hollow shaft feeds oil for the lubrication of the rocker arm.
• During oilscirculation, the oil gains heat from various engine parts, which is
given out to the sump wall. In some heavy duty engines separate oil cooler is
also employed
4. Dry Sump System:
The features of this DrySump system areas follows;
• In this system the lubricating oil is not stored in the oil sump.
• This system is employed in some racing car engines for situations where the
vehicle has to be operated at very steep angles.
• If ordinarypressuresystem of lubrication is used in such a case, the situation
may arise when there is no oil at the place where oil pump is installed.
 To avoid such situation dry sump system is used.
• Two pumps areused instead of single oil pump
• The scavenge pump A is installed in the crankcaseportion which is the
lowest.
• It pumps oil to a separate reservoir B, from wherethe pressure pump C
pimps the oil through filter D, to the cylinder bearings.
• The oil pressureis maintained at 400 – 500 kPa for main & big end
bearings.

5 Wet Sump System
 In the wet-sump lubricationsystem,the bottom of the crank case
contains an oil pan or sump that serves as oil supply, oil storage
tank and oil cooler
 The oil dripping from the cylinders, bearings and other parts, fall
under gravity back into the sump, from where it is picked up by
pump and recirculated through the engine lubrication system.
There are three varieties in wet-sump lubrication system

COMPONENTS OF LUBRICATION SYSTEM
Oil filter:
Oil filter used in the engine lubricating system of most of the motor vehicles to
filter out the dirt or grit particles from the oil.
The oil filter systems are of the two types.
1. By pass system
2. Full flowsystem
By-pass system:
In by pass system some oil goes to the engine bearing bypassing (without going
through) filter.
In this system if filter is clogged due to any reason, the engine will not halt and
graduallywhole oil gets filtered in running of engine.

Full flow system:
In full flow system whole oil passes through the filter and then goes to bearing.
In this system if filter is clogged due to any reason, the engine will halt due to
absence of oil.
Oil Pump: oil pump is generally located inside the crankcasebelow the oil level.
The function of oil pump is to supplyoil under pressureto the various engine
parts to be lubricated.

The differenttypes of the oil pumpsused for engine lubrication are as follows
1. Gear pump
2. Rotor pump
3. Plunger pump
4. Vane pump
1. Gear pump
How does a gear pump work
Gear pumps use the actions of rotating cogs or gears to transfer fluids. The
rotating element develops a liquid seal with the pump casing and creates
suction at the pump inlet. Fluid, drawn into the pump, is enclosed within the
cavities of its rotating gears and transferred to the discharge. There aretwo
basic designs of gear pump: external and internal (Figure1).
External Gear Pump

 External gear pump consists of two identical, interlocking gears supported by
separate shafts.
 One gear is driven by a motor and this drives the other gear (the idler). In
some cases, both shafts may be driven by motors.
 The shafts are supported by bearingson each side of the casing.
1. As the gears come out of mesh on the inlet side of the pump, they create
an expanded volume. Liquid flows into the cavities and is trapped by the
gear teeth as the gearscontinue to rotate againstthe pump casing.
2. The trapped fluid is moved from the inlet, to the discharge, around the
casing.
3. As the teeth of the gearsbecome interlocked on the dischargeside of the
pump, the volume is reduced and the fluid is forced out under pressure.
No fluid is transferred backthrough the centre, between the gears, because
they areinterlocked. Close tolerances between the gears and the casing allow
the pump to develop suction at the inlet and prevent fluid from leaking back
from the dischargeside (although leakageis morelikely with low viscosity
liquids).
External gear pump designs can utilise spur, helical or herringbonegears.

 An internal gear pump operates on the same principle butthe two
interlocking gears are of differentsizes with one rotating inside the other.
 The larger gear (therotor) is an internal gear i.e. it has the teeth projecting
on the inside.
 Within this is a smaller external gear (the idler – only the rotor is driven)
mounted off-centre. T
 his is designed to interlock with the rotor such that the gear teeth engage at
one point.
 A pinion and bushing attached to the pump casing holdsthe idler in
position.
 A fixed crescent-shaped partition or spacer fills the void created by the off-
centre mounting position of the idler and acts as a seal between the inlet
and outlet ports.
1. As the gears come out of mesh on the inlet side of the pump, they create
an expanded volume. Liquid flows into the cavities and is trapped by the
gear teeth as the gearscontinue to rotate againstthe pump casing and
partition.
2. The trapped fluid is moved from the inlet, to the discharge, around the
casing.
3. As the teeth of the gearsbecome interlocked on the dischargeside of the
pump, the volume is reduced and the fluid is forced out under pressure.
Internalgear pump designs only use spur gears.

Advantages
 Only two moving parts
 Only onestuffing box
 Non-pulsating discharge
 Excellent for high-viscosity
liquids
 Constant and even discharge
regardlessof pressureconditions
 Operates well in either direction
 Can be made to operatewith
one direction of flow with either
rotation
 Low NPSH required
 Single adjustable end clearance
 Easy to maintain
Disadvantages
 Usually requires
moderatespeeds
 Medium pressure
limitations
 One bearing runs in
the product
pumped
 Overhung load on
shaft bearing

 Flexible design offersapplication
customization
2. Rotary Vane Pump
 The rotor is attached to the drive shaft and is rotated by an outside
power source, such as an electric motor or gasoline engine.
 The rotor is slotted, and each slot is fitted with a rectangular vane.
 These vanes, to some extent, are free to move outward in their
respective slots.
 The rotor and vanes are enclosed in a housing, the inner surface of
which is offset with the drive axis.
As the rotor turns, centrifugal force keeps the vanes snug against the
wall of the housing. The vanes divide the area between the rotor and
housing into a series of chambers. The chambers vary in size
according to their respective positions around the shaft. The inlet port
is located in that part of the pump where the chambers are expanding
in size so that the partial vacuum (low-pressure area) formed by this
expansion allows liquid to flow into the pump. The liquid is trapped
between the vanes and carried to the outlet side of the pump. The
chambers contract in size on the outlet side, and this action forces the
liquid through the outlet port and into the system.
The pump is referred to as unbalanced because all of the pumping
action takes place on one side of the shaft and rotor. This causes a
side load on the shaft and rotor. Some vane pumps are constructed
with an elliptical-shaped housing that forms two separate pumping
areas on opposite sides of the rotor

Advantages
 Handles thin liquids at
relatively higher pressures
 Compensates for wear
through vane extension
 Sometimes preferred for
solvents, LPG
 Can run dry for short periods
 Can have one seal or stuffing
box
 Develops good vacuum
Disadvantages
 Can have two stuffing boxes
 Complex housing and many
parts
 Not suitable for high
pressures
 Not suitable for high
viscosity
 Not good with abrasives
4 Plunger Type

Plunger pumps are positive displacement devices used for pumping a
range of different liquids, including those with a relatively high
concentration of solid content
plunger pumps utilize a moving plunger in a cylinder that serves to
displace a fixed volume of fluid in each operating cycle.
The functional principle of the plunger pump
 The plunger moves forward and displaces the available volume through its
own volume and increases the pressureof the fluid to be pumped.
 The suction valve closes and the pressure valve opens the way into the
process area for the pressurized fluid.
Advantages Disadvantages
 Wide pressure range - can achieve very
high pressures
 High operating and mainten
 Pressure can be controlled without
affecting flow rate.
 Typically heavy and bulky
 Pressure and flow rate changes have
little effect on performance.
 Typically only handles lowe
 Capable of moving viscous fluids,
slurries, and abrasives with proper valve
design.
 Pulsating flow
Oil pressure Regulator valve:
 A pressureregulator is a valve that automatically cuts off the flow of oil at a
certain pressure. Regulatorsare used to allow high-pressurefluid supply
lines to be reduced to safe and usable pressures.

Operation of a pressurerelief valve
 Under normal pressureconditions, the oil pressurerelief valve is forced
down against a spring.
 Oil goes directly through the pump to the engine.
 This allows oil to flow backinto the crankcasepreventing excessive oil
pressure.
 The spring tension of the relief valve determines the maximum oil pressure.
Oil pressuregauge:
 An oil pressuregauge is mounted on the instrument panelof all cars
equipped with pressurelubricating system to tell the driver what the oil
pressureis in the engine. The oil pressure gaugesare of the following types.
1. Pressureexpansion type.
2. Electric type.
POSITIVE CRANKCASE VENTILATION:
Blow-by:

 During the combustion the gases inside the combustion chamber gets past
(leak) through piston ringsand enters the crankcase which is called blow-by.
 As blow-bycontains vapoursand sulphur, they might cause corrosion of
parts and sludge formation in lubricating oil. Hence it is importantto remove
blow-byfrom crankcase.
 Removal of blow-bycan be achieved by passing a constant stream of fresh
air through thecrankcase which is known as crankcaseventilation.
 In positive crankcase ventilation, the blow-byis returned to the engine
through the intake manifold, instead of being exhausted into the
atmosphere. (Air outshown in fig is connected to intake manifold)
CLASSIFICATION OF LUBRICATING OIL:
The classification of the lubricating oil is based on their origin; there are3 types
of lubricating oil.
A. Liquid – mineraloil, Vegetable oil animal oil etc…
B. Semi solid – greases.
C. Synthetic Lubricants.
A. LIQUID LUBRICATING OIL:
I. Mineral Oil:

These oils are derived from petroleum & are most widely used in automobiles.
The advantages are;
a. Greater chemical stability at higher temperature.
b. Lesser tendency to form emulsionswith water.
c. These areeconomical.
ii. Vegetable oil:
These areproduced from seeds, fruitsof plants, trees etc… They get oxidized
easily and become gummy.
Caster oil, once found extensive use in automobileindustry because of its high
viscosity & high film strength.
iii. Animaloil:
These areobtained from the animal fat. These are not at all suitable for
automotive engine lubrication, becausethey areoxidized easily & become
gummyafter some use.
ll. SEMI SOLID – Grease:
These aresuspension of metallic soaps (calcium or sodium soaps) dispersed in a
lubricating oil. Greasefinds use in automobiles at place where retention of
liquid lubricantsis difficult and where high temperatureis encountered e.g. -
Axles.
Grease is classified according to its purpose, like water pump grease, chassis
grease, and multipurposegrease or on the basis of type of soap base.
a) Calcium – based greases:
This grease is fairlywater proof & useful in water pumps, chassis & wheel
bearings.
b) Sodium - based grease:

This grease is able to withstand moderatelyhigh temperature& tend to absorb
water, which reduces rusting problem.
c) Aluminium - based grease:
This grease is not suitable for high temperature& are useful on chassis,
transmission & chains.
d) Lithium – based grease:
They can withstand high temperature& are used on wheel bearing, universal
joints, brake cable etc., they are also referred asmultipurposegreases.
ll. SYNTHETICLUBRICANTS:
The examples of synthetic lubricantare silicon fluid, polyglycol ethers &
aliphatic diester oils.
Following are advantagesof synthetic oil:
 Higher viscosity index.
 Reduced lacquer formation.
 Reduce loss due to evaporation.
 Considerablyless oil consumption.
 Less frequencyof changing lubricating oil.
 Less engine deposits.
 Increased fuel economy.
Cooling System
The cooling systemserves three important functions

 it removes excess heat from the engine
 it maintains the engine operating temperature where it works
most efficiently
 it brings the engine up to the right operating temperature as
quickly as possible
Components of Cooling System
Coolant
 The main purpose of the coolantin your engine is to remove the excess heat
through the radiator.
 Engine coolantis also called antifreeze because chemicals are added to keep
it from freezing in cold climates so you can continueto operateyour vehicle
In cold climate, there is always a danger that water may get frozen. The volume
of water when converted to ice increases, this may result in damageof entire
system. This may result in bursting of radiator core& cylinder jackets.
To avoid this some additives are added in the cooling water.
Someadvantages of Anti-Freeze solution are
I. The freezing pointof the water is lowered when additives areadded in
the water.
II. In hot climate, anti-freeze increases the boiling pointof the cooling
water.
Whatcauses overcooling
Overcooling most commonlyoccurswhen the coolant bypasses a defective
water temperatureregulator and flows directly to the radiator preventing the
engine from reaching normaloperating temperature

Effects of under cooling and over cooling:
 Engine should be cooled within a particular temperaturelimits.
 It should notbe too cooled or too heated up.
 Getting the engine too much cooled is called overcooling. And if the engine
is over heated it is to under cool.
 Both under cooling and over cooling have individual disadvantages.
 Over cooling results in the increase of viscosity of the lubricating oil, which in
turn result in the increase of friction between the moving parts.
If the engine gets warmed up excessively, it should be cooled so as to keep the
correct alignment of the engine. Undercooling also keeps the enginein correct
position and increase the life of the engine. Evaporation of lubricating oil that
lubricates the piston and cylinder wall is also another reason of under cooling.
This will result in metal to metal contactof the piston and cylinder wall leading
to piston crown. Burning of and warping of exhaustvalves setting up of thermal
stresses in the cylinder, cylinder head and piston. This may lead to cracking of
them.
Properties of the anti-freeze:
1) It should mix readily with water
2) It should prevent freezing of the mixtureat lowest temperature
encountered.
3) Is should circulate freely in the cooling system.
4) It should not damagecooling system by corrosiveaction.
5) It should not lose its anti-freezing propertyafter extended use.
6) It should be reasonable cheap.
7) It should not waste by evaporation.
8) It should not deposit foreign matter on the water jackets or in the
radiator.

Coolant additives:
An antifreeze is an additive which lowers the freezing point of
a water-based liquid
Commonly used coolant additives
1) Wood alcohol (Methyl alcohol)
2) Denatured alcohol(ethyl alcohol)
3) Glycerine 4) Ethylene glycol
5) Propyleneglycol
6) Mixture of alcohol & glycerine
The Alcoholis much volatile & evaporation losses are high. The mixture should
be checked regularlywith hydrometer to maintain adequatestrength.
Glycerine is less volatile but it is costly & it attacks rubber hose pipe.
Ethyl glycol is permanenttype anti freeze material because it remains liquid
even at boiling point of the water.
Glycerine & Glycol; although they are costly butthey do notevaporate easily &
hence prove cheaper in long run.
THERMOSTAT:

 The thermostat valve is used in the water cooling system to regulatethe
circulation of water in system & to maintain the normal working
temperatureof the engine partsduring the differentoperating conditions.
Working principle:
 It works automaticallyin the cooling system. When the engine is started
from cold, the thermostat valve is closed & it prevents the flow of water
from engine to radiator so that the engine readilyreaches to normal working
temperature.
 After engine reaches to desired temperaturethe thermostat valve opens.
 Thermostatvalves are most efficient over small temperaturerangeof 80˚ to
100˚C.
Location of a thermostat on an engine

Two types of thermostat valve are used in Automobile;
1) Bellows type thermostat
2) Wax type thermostat.
1) Bellows type Thermostat:
Features
 It consists of metallic bellow particularlyfilled with some volatile liquid like
acetone, alcohol or ether which boils between 70 - 85˚C.
 A valve is attached to one end of the bellows, while to the other end is
attached a framewhich fits into the cooling passage.
 The thermostat is fitted in to the coolanthose pipe at the engine outlet.
The working of bellow type thermostat

 The engine is warming up, when it is started. It is desired thatthe cooling
system should not operate so that engine warmsup quickly.
 During this temperaturethe thermostat valve remains closed, the liquid
inside the valve has not changed its state and exerts no pressureon the
valve.
 The thermostat valve is closed, while the coolantpump is running. Thus to
avoid excessive pressure build up, a bypass is provided to circulate coolant
back to the pump inlet.
 As the coolant temperaturereachesa predetermined valve (about80˚C) the
liquid inside thermostat is converted into vapour which exerts a pressure on
the valve, thus the valve opens & the water circulation through the radiator
starts.
 The valve is fully opened at about90 - 95˚C.
This is how the thermostatcontrols flowof water through theradiator
according to the engine cooling requirement.
2) Wax type Thermostat:

Operation of a Wax type thermostat
 In operation, as the wax heats up, its volume increases greatly. This has the
effect of forcing the thrust pin out.
 The thrust pin cannot move because it is mounted in a framethat is secured
to the engine block.
 However, the partof the thermostatwith the wax can move against the
spring, causing the thermostat to open.
 As the wax cools, the spring ensures the thermostat closes.
WATER EXPANSION TANK:

Instead of using overflowpipe, an expansion reservoir is provided in modern
engines.
 It is so connected with the radiator that, it receives the excess coolant as the
engine temperatureincreases due to coolantexpansion.
 When the cooling water cools down, its volume decreases and the coolant in
the reservoir returnsto the radiator keeping the system full of coolant.
 The reservoir is usually made of the translucentplastic so thatit can indicate
level of the coolant anytime.
 This system is also called as “CoolantRecovery System”.
The Expansion tank has following advantages;
1) Loss of coolantis prevented as the coolantis recovered from the expansion
tank.
2) Air does not enter cooling system with this arrangement. Thuscorrosion of
cooling jacket is prevented & deterioration of antifreeze is reduced.
3) Relatively smaller upper tank may be used with this type of radiator.
TEMPERATURE INDICATOR:
It helps the driver to prevent serious damageto the engine due to overheating.

For e.g.: If the thermostatgets stuck and does not open, the water circulation
will stop and the engine temperaturewill go very high. However, if the
temperaturegaugeis provided, the driver can stop the engine and take
preventive action against engine overheating.
Thus the temperaturegauge is necessary.
There are 2 types of temperaturegauges:
1) Bourdon tube type.
2) Electrically operated type.
1)Bourdon Tubetype:
The working of this temperature gauge:

• A bourdon tubeis placed inside the gauge, which is connected to the
element.
• The element consists of some volatile liquid and is inserted in the cooling
water circuit, generally this element is placed near the thermostat.
• As the temperatureof cooling water increases, the liquid in the element
evaporates and exerts its pressure in the capillary, which is later transmitted to
Bourdon tube.
• Dueto this pressurethe bourdon tubetries to straighten outthus moves
a pointer attached to it, to show the temperatureon the scale.
2) Electrically Operated type:
The working of this temperature gauge is explained below:

• This gauge contains an element made of such a material that its electrical
resistance decreases with increase of temperature.
• The element is connected to the coils inside the dash unit as shown in the
figure. The gaugeelement is inserted into coolant at some appropriateplace
• As the cooling water temperaturerises, the resistance of the element
decreases, which causes morecurrentto flow in the coil (2), thus increasing the
e.m.f..
• The coil (2) pullsthe armaturewhich carriesindicator pointer, thereforeas
temperatureincreases the pointer moves clockwise to show the higher
temperature.
PRESSURE CAP:
 Pressurecap formsan air tight seal due to which the coolantis maintained at
some pressure higher than the atmosphere.
 High pressure causes rise in boiling pointof the coolant. Approximatelyfor
10 kPa increase in pressure, the B.P raises by 2.5˚C
The construction features of pressure cap

 Radiator filler neck is covered with a pressurecap.
 It consists of two valves
a) Pressureblow off valve (Relief valve)
b) Vacuum valve
a) In severe working condition, the coolantstarts boiling & vaporizes, thus the
pressurein the system exceeds a certain predetermined value (50 – 100 kPa),
the pressure blow off valve
(relief valve) opens & releases the excess pressureto the atmosphere
through overflowpipe.
b) A vacuum valve is provided in the cap to admit air when pressurein the
system falls, atmospheric pressure, due to condensation of the stem vapour.
This valve operateswhen vacuum exceeds about5 kPa.
Advantagesof using PressureCap are:
 The engine can operateat higher temperaturewithoutboiling the coolant.
As the rate of the heat transfer from the cooling system to the atmosphere
depends on the
differencebetween result in additional coolanttemperature and the
atmospheric temperature, this will heat transfer to the atmosphere. This means
that for the same
engine, smaller radiator can be used.
 The preparation of air – fuel mixtureis improved at the higher operating
temperature.
 With seal cap, loss of coolantdue to evaporation is prevented.
 At high altitude, the atmospheric pressure is low, which causes the coolant
to boil at lower temperature. With pressure cap, a higher pressureis
maintained inside, irrespective of atmospheric pressure. Thus overheating of
engine is avoided.

Water / coolant Pump
The construction and the working of the water or coolantpump are discussed
below;
 A coolantpump is a necessity for the forced circulation type of engine
cooling system.
 The pump is mounted at the frontend of the engine and is driven from the
crankshaftby means of a V belt. Centrifugal type pump is the one used for
this purpose.
 The coolant from the radiator entersthe pump at the centre where the inlet
is located
 The flow of the coolantdepends on the pump speed which is proportionalto
the engine speed.

 This is desirable since at the higher engine speed moreheat will be
developed which requiresmore cooling.
 When the impeller rotates, the coolant between the vanes is thrown
outward due to the centrifugal force, thusforcing the cooled coolantat
periphery, with a forcedepending upon the speed of rotation of the pump
spindle.
 This coolant leaving the peripheryof the impeller tangentially and having
max kinetic energy then enters the involute or scroll.
 The cross section area of this scroll graduallyincreases towardsoutlet port.
Thus enlarging scroll convertskinetic energy of the coolantto pressure
energy.
In this way coolant pressureis created at the pump outlet that forcesthe
coolantthrough the cooling system.
FAN AND FAN BELT:
The purposeof the fan is to suck the air through the radiator.
• When vehicle is going at high speed, the natural flowof air passing through
radiator is sufficient for cooling.
 So the fan that is always running will be consuming unnecessary energy&
wasting the engine break power, which is not desired.
• But, when vehicle is going at low speed the natural flow of air is insufficient
to producethe desired cooling effect, here fan is required.
The construction featuresof the fan:
1. A fan is mounted behind the radiator on the same shafton which water
pump is mounted
2. It is driven by the same V belt that drives pump & the generator.
3. The fan has 4 to 7 blades.
4. It is made of moulded plastic material e.g. – Nylon or Polypropylene.

Operation of a fan
 For effective and economical running, it is required that fan must give
sufficient air flow at all vehicle loads & speed.
 Flow of the air must be optimum; it should not be excess or inadequate.
 Thus the fan running at one constantspeed is not desired; the fan must run
at variable speeds.
 The reason why fan should run at variablespeed is discussed in above given
function.
Two common fan systems are:
1) electric drive
2) viscous drive
1) electric drive
 The fan is driven by a separate electric motor which is only switched on
when the cooling water reaches a predetermined temperature(e.g. 90°C).
 The electrical circuit for the motor is controlled either by a thermostatic
switch, usually a bimetallic type, fitted in the region of the header hose, or
by a relay energized by a signal from the electronic controlunit (ECU).
 Modern engine managementsystems use a coolanttemperaturesensor to
monitor the engine temperaturefor fuelling/ignition purposes.
 The sensor signal is also used to controlthe operation of the cooling fan.
 When the engine has reached a predetermined temperaturethe engine
management
 ECU provides a controlsignal to the cooling fan relay

2) viscous drive
 This type of drive has a disc-shaped clutch plate that is placed in a container
of silicone fluid. The viscous drag of the fluid, caused by its resistance to
shear, provides a non-positivedrive that is designed to slip at an increasing
rate as the engine speed rises.
Viscous drives for fansare made in two forms:
1) torque-limiting and
2) air temperature-sensing.
The torque-limiting fan drive
 the name suggests, is capableof transmitting to the fan a maximum torque
that depends on the viscosity of the fluid.
 A clutch disc is sandwiched between the two halves of the casing, which is
fitted with fluid seals to prevent leakage of the silicone fluid. Aluminium alloy
is normallyused as a material for the disc and casing.
 This lightweight material is chosen because it has good thermal conductivity
for dissipating the heat generated by the shearing action of the fluid. Fins on
the outside of the casing also aid heat transfer from the coupling to the air.

The air-sensing fan drive,
 as well as being torque limiting, varies the fan speed to suit the temperature
of the air that has passed through the radiator.
 It does this by controlling the amountof fluid in contactwith the drive plate.
When the temperaturesensor detects that the coolant is below about75°C,
the fluid is evacuated from the drive chamber and the fan drive is
disengaged.
 This saves more power than with a torque-limiting fan and also reduces fan
noise.
Viscous Fan
RADIATOR:
The function of the radiator is to ensure close contact of hot coolantcoming out
of the engine with outside air, so as to ensure high rate of the heat transfer
from coolantto the air.
Construction:
The construction featuresof pressurecap are discussed below;

1) It consists of upper tank and lower tank. Between these tanks lies the
Core.
2) The upper tank is connected to water outlet of the engine by the hose
pipe.
3) The lower tank is connected to the water jacket inlet via a water pump.
4) Core is radiating element which cools the water.
5) An overflow pipe in header tank & drain pipe in lower tank are also
provided.
6) The size of radiator is proportional to heat energy developed in the engine
& to displacement volume of engine.
There are 2 types of radiator core:
a) Tubular type core
b) Cellular type core
a) Tubular type core:
 In this type, coolantflows through tubes & air passes around them.
 The air passing around the tubes absorb heat from the coolant.

b) Cellular type core:
• In this type, the air passes through tubes& coolantflows in the space
around them.
• The core has largenumber of individual air cells which are surrounded by
the water.
The working principle of a radiator
 The hot coolantfrom the engine enters the radiator atthe top.
 The cross flow of air, cools down the coolantin the radiator core. When the
coolantis cooled it flows downwards.
 Thus the coolant is collected in the collector tank from whereit is pumped to
the engine for engine cooling purpose.
Material used:
• Copper & yellow brass; are used due to high thermal conductivity & good
resistance to corrosion.
• Aluminium is also used because it is light in weight and is economical.

TYPES OF ENGINE COOLING SYSTEM:
There are 2 methods for cooling of automobileengine; they are A) Air cooling
system
A) Air Cooling System:
B) Water Cooling system
Air Cooling system
 Currentof air flows over the heated metal surfacefrom where the heat is to
be removed.
 The heat dissipated depends upon following factors:
a) Surfacearea of the metal into contact with air.
b) Mass flow rate of the air.
c) Temperaturedifferencebetween the heated surfaceand air.
d) Conductivity of the metal.
 Thus for an effective cooling the surfacearea of the metal which is in contact
with the air should be increased. This is doneby using “fins” over the
cylinder barrels.

Advantages of Air cooling system
1) It is lighter in weight due to the absence of the radiator, cooling jackets
and coolant.
2) Maintenanceis easier the problem of leakage does not exist.
3) Anti-freezeis not required.
4) Engine warmsup faster than water cooled design.
5) It can operatein cold climate where water may freeze.
6) It can be used in areas wherethere is scarcity of the cooling water.
Disadvantages of Air cooling system:
1) Less efficient cooling, because the coefficientof the heat transfer for the
air is less than that for water.
2) It is not easy to maintain even cooling all around thatcylinder, distortion
of the cylinder may take place.
3) Limited use in motor cycle and scooters where cylinders are exposed to
air stream.
4) Morenoisy operation.
Water Cooling system
In water cooling system, the cooling medium used is water.
 In this system engine cylinder aresurrounded bythe water jackets through
which cooling water flows.
 Heat flows from the cylinder wall into water, which goes to radiator; water is
cooled by air drawn through radiator.

 Usually antifreeze is added to cooling water, which it is often referred as
“coolant”.
Water cooling systems are of 2 types:
I) Thermo-syphon system
II) Pump Circulation system
I) Thermo-syphon system:
 The coolant is made to circulate around thecooling system so that heat
absorbed by the coolant from the cylinders can be dissipated in a radiator.
 The simplest method of producing thiscirculation relies upon convection
currentsin the coolant. These result from the reduction in density caused by
expansion of the coolantwith increase in temperature.
 A system using this method of circulation is known as a ‘natural circulation
system’, or a ‘thermo-syphon system’.
 The basic system consists of a water jacket, which is connected by a
synthetic rubber hoseto a header tank
 This tank formspart of the radiator, which is a heat exchanger madeby
connecting two tanks (header and lower) with a number of finned tubes to
providea large surfacearea for the disposal of unwanted heat. Airflow over
the tubes and fins carriesaway the heat radiated from the hot coolantand
so lowers the temperature of the coolant as it passes down the tubes.
 A bottom hose connects the lower tank to the engine water jacket to
providea return path to the engine for the coolant.
 When the engine is running and the vehicle is either stationaryor travelling
slowly, the airflowthrough the radiator is insufficient to give adequate
cooling. At
 these times overheating is avoided by using a fan to act as an air pump.
Energy to drive the fan is supplied by a vee-belt from the crankshaft, or
alternatively the fan can be driven directly by an electric motor.

The principleof operation is based on the three means of heat transfer:
conduction,
convection and
radiation.
Cooling of the engine takes place in this sequence.
Conduction
 Heat flows from a hotsubstance to a cold substance.
 The hot internalparts of the cylinder pass the heat from one metal particle
to the next through the walls to the comparatively coolouter surface.
 Coolantin contact with the metal surfacereceives the heat and carriesit
away.
Convection
 This is based on the principlethat as the temperatureof water rises from
4°C, it gets lighter, i.e. its density decreases as the temperatureincreases.
 Coolantin the water jacket becomes heated, and since it becomes lighter it
rises to the top of the jacket and flows through theheader hose to the
radiator.
 The hot water in the jacket is replaced by colder water fed in from the lower
tank of the radiator.
 When the flowis combined with the upward flowin the jacket, a natural
circulation of the coolantis achieved which is called ‘convection’.
 Circulation due to the thermo-syphon action can only take place if the
coolantlevel in the header tank is above the level of the header hose.
Radiation
 Heat travels through air in a wave form similar to light.
 Radiated heat can be felt if your hand is placed close to a hot surface.
 The purposeof a radiator is to transfer the heat from the coolantto the air.

 The air must move because, if it is stationary, the air temperaturewill soon
become close to the coolanttemperatureand heat transfer will be very
slow. To avoid this problem, cold air is continuously supplied to the radiator
through vehicle motion or using a fan, and thus heated air is also carried
away.

II) Pump Circulation system:
The features of this water cooling system are as follows:
1) In this water cooling system, the circulation of the water is obtained by a
pump.
2) Pump is driven by means of a V belt placed on a pulley which is mounted
on the crankshaft.
3) This system is effective; water circulation becomes faster as engine speed
increases. There is no need to maintain water at correctlevel.

This system has following advantages over Thermo-syphon system:
1) Circulation of the coolantis proportional to both the engine load and
speed.
2) Radiator header tank is not necessary, unlike Thermo-syphon system.
3) Circulation of coolantis positive, hence its moreefficient due to which
the smaller water jacket can be used, resulting in overall decrease of engine
size.
4) Even radiator does not need to be placed in front. Itcan be placed in rear
or side as per design conditions.
Comparison between Air cooled and water cooled system:
Air Cooling system
1. In this system, cooling
medium used is air.
2. The engine design is simple.
3. The air cooled engine is less
sensitive to climate condition.
No antifreeze solution is
needed. Dueto greater
temperature difference
between cooling air and cylinder.
.
4. Air cooling system has no
maintenance.
5. The warm up performanceis
better; this results in low cylinder
wear.
.
Water Cooling system
In this system, cooling medium used is
water.
The engine design is complex.
Cold water starting requiresanti-freeze
solution which may deposit on cylinder
wall on water side & the engine
performancebecomesmoresensitive
to climate conditions. result in reduced
heat transfer
It requiresmaintenance; slight leakage
of radiator mayresult in engine
breakdown.
Warm up performanceis poor. The
result in greater cylinder wear

6. Size of engine is small &
weight is less as there are no water
jacket, radiator & water pump.
7. Air cooled engine must be
installed in front side of the vehicle.
8. Volumetric efficiency is lower
due to high cylinder head
temperature
9. Example: Bikes, Scootersetc…
Size & weight of the engine is
increased dueto use of radiator, pump
etc...
Water cooling engine can be installed
anywhere on the vehicle.
Volumetric efficiency is higher than air
cooled engine.
Example: Cars, Bus, Trucksetc…

Introduction to lub and cooling sys

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