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COOLING SYSTEM
A system, which controls the engine temperature, is known as a cooling system
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(Platinum, a
metal which has one of the highest melting points, melts at 1750 °C, iron at 1530°C and
aluminium at 657°C
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• Due to very high temperatures, the film of the lubricating oil will get oxidized, thus producing
carbon deposits on the surface
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• Due to overheating, large
temperature differences may lead to a distortion of the engine
components due to the thermal stresses set up
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• Higher temperatures also lower the volumetric efficiency of the engine
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It must be capable of removing only about 30% of the heat generated in the combustion chamber
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2
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During the starting of the engine, the
cooling should be very slow so that the different working parts reach their operating temperatures in a short
time
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AIR COOLING SYSTEM
In this type of cooling system, the heat, which is conducted to the outer parts of the engine, is radiated and
conducted away by the stream of air, which is obtained from the atmosphere
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The fins are metallic ridges, which are formed during the casting of the cylinder and cylinder head
The amount of heat carried off by the air-cooling depends upon the following factors:
(i)
The total area of the fin surfaces,
(ii)
The velocity and amount of the cooling air and
(iii)
The temperature of the fins and of the cooling air
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Air-cooling is
also provided in some small industrial engines
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A blower is used to provide air
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Its design of air-cooled engine is simple
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It is lighter in weight than water-cooled engines due to the absence of water jackets, radiator,
circulating pump and the weight of the cooling water
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It is cheaper to manufacture
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It needs less care and maintenance
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This system of cooling is particularly advantageous where there are extreme climatic
conditions in the arctic or where there is scarcity of water as in deserts
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No risk of damage from frost, such as cracking of cylinder jackets or radiator water tubes
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b) It keeps the engine at working temperature for efficient and economical working
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Though the present tractor has a forced circulation system, it is still worthwhile to get acquainted with the
other three systems
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The water from a storage tank
is directly supplied to the engine cylinder
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The
low H
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engine, coupled with the irrigation pump is an example
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In this system the radiator is placed at a higher level than the engine for the easy flow of water
towards the engine
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As the water jacket becomes hot, it rises to the top of the radiator
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This helps in keeping the engine at working temperature
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2
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3
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For these
reasons this system has become obsolete and is no more in use
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In this there is a hopper on a jacket
containing water, which surrounds the engine cylinder
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An engine fitted with this system cannot run for several hours without it being
refilled with water
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After the circulation water comes back to the radiator, it loses its heat by the process of
radiation
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Parts of Liquid Cooling System
The main parts in the water-cooling system are: (i) water pump, (ii) fan, (iii) radiator and pressure cap, (iv)
fan belt (v) water jacket, (vi) thermostat valve, (vii) temperature gauge and (viii) hose pipes
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It is centrally mounted at the front of the cylinder block and is usually
driven by means of a belt
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The bottom of the radiator is connected to the suction side of the pump
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Seals of various designs are incorporated in the pump to prevent loss of coolant from the system
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It serves two purposes in the cooling system of a engine
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(b) It throws fresh air over the outer surface of the engine, which takes away the heat conducted by
the engine parts and thus increases the efficiency of the entire cooling system
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The radiator consists of
three main parts: (i) upper tank, (ii) lower tank and (iii) tubes
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The
heat contained in the hot water is conducted to the copper fins provided around the tubes
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There are three
types of radiators: (i) gilled tube radiator, (ii) tubular radiator (Fig
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c)

Type of radiators
Gilled tube radiator:
This is perhaps the oldest type of radiator, although it is still in use
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Each tube has a large number of annular rings or fins pressed firmly over its outside surface
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The radiator vertical tubes pass through thin fine copper
sheets which run horizontally
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In this, the clogging of any passage affects only a small parts of the cooling
surface
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Thermostat Valve
It is a kind of check valve which opens and closes with the effect of temperature
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During the warm-up period, the thermostat is closed and the water pump circulates the
water only throughout the cylinder block and cylinder head
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8
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Standard thermostats are designed to start opening at 70 to 75°C and they fully open at 82°C
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), start opening at 80 to
90°C and fully open at 92°C
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Bellow type valve: Flexible bellows are filled with alcohol or ether
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When the unit is cooled, the gas condenses
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Bimetallic type valve: This consists of a bimetallic strip
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Pellet type valve: A copper impregnated wax pellet expands when heated and contracts when cooled
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A coil spring closes the valve when the pellet contracts
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But when water is boiled in a closed radiator under high pressure, the
boiling temperature of water increases
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Therefore, a pressure-type radiator cap is used with the forced circulation cooling system
(Fig
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6a)
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The pressure-release valve is set to
open at a pressure between 4 and 13 psi
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Any increase in
pressure is released by the pressure release valve to the atmosphere
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To
overcome this problem the pressure release valve is associated with a vacuum valve which opens the
radiator to the atmosphere
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In cold areas, if the engine is kept without this
solution for some time, the water may freeze and expand leading to fractures in the cylinder block, cylinder
head, pipes and/or radiators
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An ideal mixture should
easily dissolve in water, be reasonably cheap and should not deposit any foreign matter in the jacket pipes
and radiator
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The materials commonly used are wood
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alcohol, denatured alcohol, glycerine, ethylene, glycol, propylene glycol, mixtures of alcohol and glycerine
and various mixtures of other chemicals
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The commercial cleaning compounds available must be
carefully used in accordance with the manufacturers' instructions
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If a considerable amount of scale and rust has
accumulated, it may not be possible that cleaning alone will remove it
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Cooling System Cleaning Procedure
It involves the following steps
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Drain the system by opening the drain cocks
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Fill up this solution in the radiator and engine block and run the
engine on idle load for 8 to 10 hours
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2
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This solution is allowed to remain in the system for 2 to 3 hours at normal load
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3
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(a) Straight flushing: Connect the lead-away hose to the water outlet connection on the engine
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Turn on the water until the
water passages are filled and the release the air in short blasts, allowing the water to fill the engine after
such blasts
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The procedure for this is outlined below:
(i) Radiator: Disconnect the top hose of the radiator from the engine and attach a lead-away hose to the
radiator
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Connect
water and air hoses to the gun
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Release the air in short
blasts and allows the water to fill the radiator between each blast
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Follow the same procedure
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C
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Due to continuous movement of two metallic surfaces over
each other, there is wearing moving parts, generation of heat and loss of power in the engine lubrication of
moving parts is essential to prevent all these harmful effects
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(a) Reducing frictional effect: The primary purpose of the lubrication is to reduce friction and wear
between two rubbing surfaces
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The continuous friction
produce heat which causes wearing of parts and loss of power
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This can be done by proper lubrication only
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Lubrication also reduces noise produced by the movement
of two metal surfaces over each other
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Lubrication creates cooling effect on the engine parts
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Thus, it prevents leakage of gases from the engine cylinder
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Lubrication theory: There are two theories in existence regarding the application of lubricants on a
surface: (i) Fluid film theory and (ii) Boundary layer theory
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It produces a rolling effect, which reduces friction
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Thus the sliding surfaces are kept apart from each other, thereby reducing friction
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It becomes waxy and gummy which is not very suitable for machines
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Cottonseed oil, olive oil, linseed oil and
castor oil are used as lubricant in small Simple machines
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It is obtained from crude petroleum found in
nature
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A good
lubricant should have the following qualities:
1
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It should remain stable under changing temperatures
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It should keep lubricated pans clean
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It should not corrode metallic surfaces
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The parts which require lubrication are: (i) cylinder walls and piston (ii) piston pin (iii) crankshaft and
connecting rod bearings (iv) camshaft bearings (v) valves and valve operating mechanism (vi) cooling fan
(vii) water pump and (viii) ignition mechanism
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SPLASH SYSTEM
In this system, there is an oil trough, provided below the connecting rod
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This is obtained by maintaining a continuous flow of oil from the oil sump or
reservoir into a splash pan, which has a depression or a trough like arrangement under each connecting rod
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A dipper is
provided at the lower end of the connecting rod
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The splashing action of oil maintains a fog or mist of oil that drenches the inner parts of the engine
such as bearings, cylinder walls, pistons, piston pins, timing gears etc
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For effective functioning of
the engine, proper level of oil maintained in the oil pan
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This system is very effective if the
oil is clean and undiluted
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There is every possibility that oil may become very thin through crankcase dilution
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FORCED FEED SYSTEM
In this system, the oil is pumped directly lo the crankshaft, connecting rod, piston pin, timing gears and
camshaft of the engine through suitable paths of oil
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From this pipe, it goes to each of the main bearings through
holes
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From there, it goes to lubricate the walls, pistons and rings
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Lubricating oil pump is a positive displacement pump, usually gear type or vane'
type
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Forced feed lubrication system
The excess oil comes back from the cylinder head to the crankcase
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This system is commonly used on high speed
multi-cylinder engine in tractors, trucks and automobiles
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The rest of the parts like cylinder liners, cams, tappets etc are
lubricated by splashed oil
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The pump is driven by the camshaft of t engine
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A portion of the oil forced to the oil
filter and the remaining oil goes to lubricate various par of the engine
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About 3 kg/sq cm (45 psi) pressure is developed in
the lubrication system of a tractor engine, [f the oil pressure gauge
indicates no pressure in the line, there is some defect in the system
which must be checked immediately
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OIL FILTER: Lubricating oil in an engine becomes contaminated with various materials such as dirt,
metal particles and carbon
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It is a type of
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strainer using cloth, paper, felt, wire screen or similar elements
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Wearing of parts, oil consumption and operating
cost of an engine can be considerably reduced by proper
maintenance of oil filters
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(i) Full flow filter: In this filter the entire quantity of oil is forced
to circulate through it before it enters the engine
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Filter element consists
of felt, cloth, paper and plastic
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(ii) By pass filter: In this type of filter, the supply lines are from
the pump and are connected to permit only a part of the oil
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Over a period of operation, all the oil in the crankcase passes
through the filter
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It serves to warn
the operator of any irregularity in the system
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The purpose of the breather is to prevent building up
pressure in the crankcase
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TROUBLES IN LUBRICATION SYSTEM
There are a few common troubles in lubrication system such as: (1) Excessive oil consumption (2) Low oil
pressure and (3) Excessive oil pressureExcessive oil consumption: When there is excessive oil consumption in the engine, the reasons arc : (a)
more oil goes to combustion chamber and gets burnt (b) some leakage occurs in some part of - the line and
(c) loss of oil in form of vapour through ventilating system
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Low oil pressure: Low oil pressure can result due to: (i) weak relief valve spring (ii) worn oil pump (iii)
cracked oil line (iv) obstruction in the oil lines (v) very thin oil and (vi) worn out bearings
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Sometimes defective oil pressure indicator shows low oil pressure
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Excessive oil pressure: Excessive oil pressure may result due to : (i) stuck relief valve (ii) strong valve
spring (iii) clogged oil line and (iv) very heavy oil
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Sometimes
defective oil pressure indicator records high oil pressure
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CARE AND MAINTENANCE OF LUBRICATION SYSTEM
The following are few suggestions for good lubrication system:
• A good design of oil circulation system should be chosen
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• Oil should be maintained at desired level in the oil chamber
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• Connections, pipings, valves and pressure gauge should be checked regularly
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Before putting the new oil, the
crankcase should be cleaned and flushed well with a flushing oil
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