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chapter one Internal Combustion Engine cooling system

11

CHAPTER ONE

INTERNAL COMBUSTION

ENGINE COOLING

SYSTEM

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1-1 I ntroduction

The function of the cooling system is to

remove the heat from the engine adequately

to keep the temperature inside the enginewithin certain limits. The cooling system could

be by water circulated in the system or by air

A typical energy balance in a DG set indicates

following break-up :

Input : 100% Thermal Energy

Outputs: 33% of this total heat is converted into crankshaft horsepower

(Electrical Output )

30% is expelled through exhaust (Stack Loss through Flue Gases)

7% is radiated directly into the atmosphere from engine surfaces

30% must be dissipated through a carefully designed cooling system

(coolant losses)

The cooling system must remove heat in order to keep the engine atthe correct operating temperature.

1-2 Bad effect of h igh temperature in the engine

(i) Cylinder and piston may expand to such an extent that thepiston would seize in the cylinder and stop the engine.

(ii) lubricating quality of the oil inside the cylinder would bedestroyed due to high temperature and there may not be sucking of

air in the cylinder.

(iii) Pr-ignition of fuel mixture would take place and would causeengine knocking as well as loss of power.

Figure(1-1):cooling system

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For satisfactory performance of the engine, neither overheating nor

overcooling is desirable. Experiments have shown that best operating

temperature of I.C engine lies between 140F to 200 F, depending upon

types of engines and load conditions.

1-3 types of Cool ing System

1- water cooling systems using a radiator and a fan to remove the heat from

the engine and other systems on a machine.

2- air cooling systems using a heat exchanger, keel coolers, or cooling

towers to remove heat.

1-4 Ai r cooli ng system

The air cooling system have metal FINS on the

outer perimeter of the engine. Heat is

transferred from the engine, through these fins,

into the atmosphere.

Principle of air cooling

The cylinder of an air cooled engine has fins

to increase the area of contact of air for speedy cooling. The cylinder isnormally enclosed in a sheet metal casing called Cowling. The flywheel

has blades projecting from its face, so that it acts like a fan drawing air

through a hole in the cowling and directing it around the finned cylinder. For

maintenance of air cooling system, passage of air is kept clean by

removing grasses etc. This is done by removing the cowling and

cleaning out the dirt etc. by a stiff brush or compressed air. When

separate fan is provided, the belt tension is to be checked and adjusted if

necessary.

Advantages of air cooling

It is simpler in design and construction. Water jackets, radiators, water

pump, thermostat, pipes, hoses etc. are not needed. It is more compact.

It is comparatively lighter in weight.

Figure(1-2):air cooling system

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Disadvantages

There is uneven cooling of the engine parts. Engine temperature is

generally high during working period.

1-5 Water and ai r cool ing system

Engines, using water as cooling medium is called water cooled

engines. The liquid is circulated round the cylinders to absorb heat from

the cylinder walls. In general, water is used as cooling liquid. The

heated water is conducted through a radiator which helps in cooling the

water. There are three common methods of water cooling: (i) Open jacket or

hopper method, (ii) Thermo siphon method, and (iii) Forced circulation

method.

1-5-1 Forced circulation method

In this method, a water pump is used to force water from the radiator to

the water jacket of the engine. After circulating the entire run of water

jacket, hot water goes to the radiator, where it passes through tubes

surrounded by air. A fan is driven with the help of a V-belt to suck air

through tubes of the radiator unit, cooling radiator water. To maintain the

correct engine temperature, a thermostat valve is placed at the outer end of

cylinder head. Cooling liquid is by-passed through the water jacket of

the engine until engine attains the desired temperature. Then thermostat

valve opens and the by-pass is closed, allowing the water to go to the

radiator.

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1-5-2 basic Components of Cooling

System

water pump engine oil Cooler water temperature Regulators fan radiator radiator cap coolant

1-5-3 Jacket Water After cooler

(JWAC) Operation

* coolant flows to jacket water pump

(1) through an elbow that connects to

the radiator or heat exchanger (11).

Part of the coolant is sent to the

aftercooler while most of the coolant is

sent through engine oil cooler (3).

* the coolant that is sent to theaftercooler goes through the aftercooler

core (7). The coolant then goes through

an elbow. The coolant goes into a

passage in the block. The passage is

near the center of the view at the rear of the block. The coolant that is sent to

the engine oil cooler goes through the engine oil cooler. The coolant flows

into the water jacket of the block at the right rear cylinder. The cooler

coolant is mixed with the hotter coolant. The mixture goes to both sides of

the block through distribution manifolds. The distribution manifolds are

connected to the water jacket of all the cylinders. The main distribution

manifold is located just above the main bearing oil gallery.

Figure(1-3):typical cooling system

Figure(1-5):(JWAC) Operation

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* the coolant flows upward through the water jackets. The coolant flows

around the cylinder liners from the bottom to the top. Near the top of the

cylinder liners, the water

jacket is made smaller. This is

the area that has the hottesttemperature. This smaller area

causes the coolant to flow

faster for better liner cooling.

Coolant from the top of the

liners flows into the cylinder

head which sends the coolant

around the parts that have the

hottest temperature.

* Coolant flows to the top of the

cylinder head (one at each cylinder). The coolant flows out of the cylinder

head through an elbow into water manifold (6). Coolant then flows through

the manifold to the temperature regulator housing (thermostat).

* regulator housing (8) has an upper flow section and a lower flow section.

The regulator housing uses four temperature regulators. The sensing bulbs of

the four temperature regulators are in the coolant in the lower section of thehousing. Before the regulators open, cold coolant is sent through the bypass

line back to the inlet of the water pump. As the temperature of the coolant

increases, the regulators start to open. When the regulators open the coolant

flow in the bypass line is then restricted. Coolant is sent through the outlets

to the radiator or heat exchanger (11) .

Separate Circuit Aftercooler (SCAC) Line Diagram

1. Cylinder block2. Engine oil cooler3. Regulator housing4. Jacket water pump

Figure(1-5):cooling system

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5. Coolant tank for jacketwater

6. Aftercooler7. Thermostatic valve8. Separate circuit water

pump

9. Radiator

Separate Circuit After cooler (SCAC) Operation

* coolant flows to separate circuit water pump (8). The coolant flowsthrough an elbow that connects to the coolant tank for the separate circuit

(9). The coolant flow is sent through aftercooler (6) .

*coolant flows through aftercooler (6) and back to thermostatic valve (7).

Before the thermostatic valve opens, cold coolant is sent back to separate

circuit water pump (8). As the temperature of the coolant increases, the

regulators start to open. When the regulators open the coolant flow in the

bypass line is restricted .

* the coolant is then sent through the outlet to radiator (9) for the separate

circuit cooling system .

Air to Air After Cooler

The air is cooled by radiator fan

which is fitted beside radiator or

in front of radiator depending

upon applications.

Figure(1-5):(SCAC) Line Diagram

Figure(1-6):Air to Air After Cooler

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1-5-4 Water jacket Pump

Jacket water pumpMounted on RH side of the engine, gear driven, supply

and pump the coolant into the engine for cooling. The water pump (also

called a coolant pump) is driven by a belt from the crankshaft or driven bythe camshaft.

1-5-5 Radiator

Radiator : Reduces the coolant temperature with help

of fan driven by belt, transfers heat from the coolant to

air passing through it ,and is a series of tubes and fins

that expose the heat from the engine coolant to the

most surface area possible, maximizing heat transfer.

Radiator is a device for cooling the circulating water

in the engine. It holds a large volume of water in close

contact with a large volume of air so that heat is transferred from the water

to the air easily. Hot water flows into the radiator at the top and cold

water flows out from the bottom. Tubes or passages carry the water

from the top of the radiator to the bottom, passing it over a large

metal surface. Air flows between the tubes or through the cells at

right angles to the downward flowing water. This helps in transferring

the heat from the water to the atmosphere. On the basis of fabrication,

the radiator is of two types: tubular type and cellular type.

Figure(1-7):Water jacket Pump

Figure(1-8):Radiator

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Tubular type radiatorIt has round or flat water tubes, leading from the top to the bottom of the

radiator. They may be soldered, brazed or welded in place or fastened bymeans of a stuffing box at each end. Fins or folded strips of light sheet

metal, placed between the tubes, increase the radiating surface and

improve the heat transfer.

Cellular type radiatorIt has a core made of short air tubes which

are laid horizontally and soldered together

at the ends with space between them to

allow water to flow. It is also called Honey

comb type radiator.

Radiators are also classified according to the

direction of the water flow through them. In

some, the water flows from top to bottom

down flow type radiators. In other, the

water flows horizontally from an input

tank on one side to another tank on theother side cross flow type radiator

.Radiators are usually made of copper and brass because of their high heat

conductivity. The various sections of the radiator are most completely joined

together by soldering.

Radiator Pressure Cap Purpose

The radiator cap contains a relief valve which

limits the amount of pressure developed in thesystem. It is important to maintain the correct

pressure in the cooling system because the

boiling point of the coolant is increased

as the pressure increases. By increasing

the pressure of the cooling system by 7

Figure(1-9):Cellular type radiator

Figure(1-10):Radiator Pressure Cap

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kPa (1 psi) the boiling point of the coolant is raised by 1.8C (3.25F).

Operation

The pressure cap contains a large

spring and a pressure valve as shown

in fig(1-11).When pressure in the

cooling system is low, there is not

enough force to lift the valve off its

seat. Pressure will build up in the cooling

system until it is high enough to

overcome spring force. The valve will

then lift off its seat and prevent

excessive pressure build up in thesystem. When the engine is shut down,

the coolant contracts. If air in the top

tank was vented during operation, this

must now be made up to prevent a

pressure less than atmospheric in the

cooling system. This is achieved by the

small vacuum valve in the center of the

large disc valve. The small valve openswhen the atmospheric pressure is greater

than the light spring pressure plus

radiator pressure. Many highway

vehicles use an expansion tank (or

reservoir) which is piped to the vent tube

on the right side of Fig(1-13). In this

situation, the cooling system is

replenished with coolant from the expansion tank when the system cools

down. The pressure cap also allows for coolant level inspection and

replenishment. In general the coolant should always come up to the bottom

of the filler pipe. When the system is fitted with a coolant recovery system

(expansion tank or reservoir), the level is normally checked in the recovery

container.

Figure(1-11):Coolant expanding

Figure(1-12):Coolant contracting

Figure(1-13):reservoir

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Functions of Radiator Cap

* Seal during engine operation ,withstands high temperature, leak proof

during engine operation, and operates at 7 psi depending upon radiator cap

and releases excess pressure.

* The pressure cap contains a pressure valve that allows for a pressure

increase in the cooling system, which raises the coolants boiling point.

The pressure is caused by coolant expansion as the engine warms

*The cap also contains a vent (vacuum) valve to allow coolant to re-enter the

radiator as the system cools and the coolant contracts.

1-5-6 Temperature Regulator

The function regulators housing and the temperature bulb for opening and

closing of the regulators. maintain engine working temperature and control

the maximum outlet water temperature.

Thermostat temperature control [3 ]

There is a normal operating temperature range between low temperature and

high-temperature extremes, The thermostat controls the minimum normaltemperature, The thermostat is a temperature-controlled valve placed at the

engine coolant outlet, An encapsulated, wax-based, plastic-pellet heat sensor

is located on the engine side of the thermostatic valve, As the engine warms,

heat swells the heat sensor, A mechanical link, connected to the heat sensor,

Figure(1-14):Thermostat

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opens the thermostat valve, As the thermostat

begins to open, it allows some coolant to flow to

the radiator, where it is cooled.

1-6-7 Cooling fans

Air is forced across the radiator core by a

cooling fan on older engines used in rear-wheel-

drive vehicles, it is attached to a fan hub that is

pressed on the water pump shaft typical electric

cooling fan assembly shown the radiator and

related components.

Thermostatic fans

The thermal fan is designed so that it uses little power at high enginespeeds and minimizes noise.

The thermal fan has a silicone coupling fan drive mounted betweenthe drive pulley and the fan.

A second type of thermal fan has a thermostatic spring added to thesilicone coupling fan drive .

The thermostatic spring operates a valve that allows the fan tofreewheel when the radiator is cold

As the radiator warms to about 150F (65C), the air hitting thethermostatic spring will cause the spring to change its shape.

Figure(1-15):Thermostat Operation

Figure(1-16):Cooling fans

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Radiator Shroud

Fan and radiator design on high output engines usually incorporate a fan

shroud. The fan shroud is a shaped metal

or plastic cover that prevents the escapeof fan air and directs air flow into the fan.

Use of the shroud ensures that the

maximum amount of air that the fan

moves, actually passes through the

radiator. Without a shroud, air may just

circulate at the tip of the fan blades. The

position of the fan within its shroud is

important to the shroud's effectiveness.1-6-8 BLOCK HEATER

Fitted into the block to keep the engine warm

during extremely cold weather.

Water Jackets

* Water jackets are hollow passages in the block

and cylinder head(s) that surround the areas

closest to the cylinders and combustion

chambers.

Figure(1-16):radiator shroud design

Figure(1-10):BLOCK HEATER

Figure(1-11):Water jackets

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1-6 Disadvantages of overcool ing & under cooli ng

Engine should be cooled within a particular temperature limits. It should not

be 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 undercooling 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. Under cooling also keeps the engine in 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 contact of the piston and cylinder

wall leading to piston crown. Burning of and warping of exhaust valves

setting up of thermal stresses in the cylinder, cylinder head and piston. This

may lead to cracking of them.

1-7 Cooling System Maintenance

The condition must be found in coolant water

Coolant - water combined with corrosion inhibitors or water combined with

antifreeze and corrosion inhibitors

Heat Transfer - Tendency of heat to move from a hot area to a cooler area.

Protection Against Freezing of the Coolant - best protection against coolant

freezing is the correct mixture/ratio of the coolant. The most common

antifreezes is use of ethylene glycol to provide freeze protection.

Corrosion Resistance - Coolant must prevent the formation of rust and pits

in the engine and other components.

For example Add Cat SCA (Supplemental Cooling Additive), or Cat ELC

(Extended Life Coolant) or Cat DEAC (Diesel Engine Antifreeze/Coolant).

Scale and Deposits - Water used as a coolant determine scale and deposit

formations. The water must be pretreated.

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Compatibility - Coolant must not damage seals, hoses or any of the materials

used in construction of cooling systems such as copper, aluminum, and steel.

Non foaming - The coolant used in a system must not foam or make sludge

that can damage the cooling system.

Sediment - The coolant must be clear and not have mud or an oil residue in

it.

Cleaning the radiator exterior

Overheating can result from exterior radiator plugging as well asinternal plugging.

External plugging is caused by dirt and insects.

This type of plugging can be seen if you look straight through theradiator while a light is held behind it

It is most likely to occur on off-road vehicles.The plugged exterior of the radiator core can usually be cleaned with

water pressure from a hose.

The water is aimed at the engine side of the radiator.The water should flow freely through the core at all locations. If this does not clean the core, the radiator should be removed for

cleaning at a radiator shop.

Flush And Refill

Manufacturers recommend that a cooling system be flushed and thatthe antifreeze be replaced at specified intervals.

Draining coolant when the engine is cool eliminates the danger ofbeing injured by hot coolant.

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The radiator is drained by opening a petcock in the bottom tank, andthe coolant in the block is drained into a suitable container by opening

plugs located in the lower part of the cooling passage.

Water should be run into the filler opening while the drains remainopen.

Flushing should be continued until only clear water comes from thesystem.(most antifreeze coolant is ethylene glycol-based)

Quick and Easy Cooling System Problem Diagnosis

If overheating occurs is slow, stop-and-go traffic, the usual cause is low

airflow through the radiator. Check for airflow blockages or cooling fan

malfunction. If overheating occurs at highway speeds, the cause isusually a radiator or coolant circulation problem. Check for a restricted or

clogged radiator.

1-8 Common Causes Of Overheating

Overheating can be caused by defects in the cooling system , Some

common causes of overheating include:

Low coolant levelPlugged, dirty, or blocked radiatorDefective fan clutch or electric fan Incorrect ignition timingLow engine oil levelCrankcase oil level too high: Crankshaft dips in oil and causes a

corresponding increase in temperatures due to friction and parasiticload on the engine. Crankshaft oil dipping can also be encountered

when operating an engine beyond the angles for which the oil pan

was originally designed.[7]

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Poor circulation of coolant caused by collapsing of soft hose andrestriction

Dirty engine exterior: Heavy accumulations of dirt and grease canseverely hinder normal heat dissipation through the exterior wallsof all the engine components.

Pressure of air in the cooling system: The following are the mostcommon causes of air entrapment:-

a- Low coolant level due to leaking water pump or leaks at hose

and/or coolant accessories.

b- Leaking air intake aftercooler.

c- Leaking engine or air compressor cylinder head gasket.

d- Improperly seated injector sleeve.

Inadequate cooling capacity: This condition can be the result ofmisapplication of one or any combination of the following coolingsystem components:-

A. Radiator B. Top Tank

C. Surge Tank D. Fan

E. Fan Shroud F. Water Pump

G. Auxiliary Coolers H. Re-circulation Baffles

I. Fan Speed [7]

Broken fan beltDefective radiator capDragging brakesFrozen coolant (in freezing weather)Defective thermostat

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Cavitation corrosion of liners and water pump impellers.[6]Hot spots that can cause piston scoring, cracked injector sleeves,

and cracked heads.[6]

Low coolant temperature.[6]Solder Corrosion.[6]Defective water pump (the impeller slipping on the shaft

internally)

How Much Coolant Can a Water Pump?

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 20times per minute. 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 miles per

hour (56 kilometers per hour), the typical water pump still moves about

2,000 gallons (7,500 liters) per hour or 1/2 gallon (2 liters) per second!

Common Causes of Water Pump Bearing Failure

* improper drive belt tension (both too little or too much tension)

* abent fan

* a missing piece of fan blade

* a cracked fan blade

* fan mounting surfaces that are not flush

* a worn fan clutch

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Testing The Cooling System Pressure Testing

Pressure testing should be performedwhenever there is a leak or suspected leak.

The pressure tester can also be used to testthe radiator cap.

An adapter is used to connect the pressuretester to the radiator cap.

Replace any cap that will not holdpressure.

Testing The Cooling System Coolant Dye

Leak Testing

One of the best methods to check for a coolant leak is to use afluorescent dye in the coolant.

Operate the vehicle with the dye in the coolantuntil the engine reaches normal operating

temperature.

Use a black light to inspect all areas of thecooling system.

When there is a leak, it will be easy to spotbecause the dye in the coolant will be seen

as bright green.

Use Distilled Water in the Cooling System

Two technicians are discussing refilling the radiator after changingantifreeze. One technician says that distilled water is best to usebecause it does not contain minerals that can coat the passages of

the cooling system. The other technician says that any water that is

suitable to drink can be used in a cooling system. Both technicians

are correct.

Figure(1-12):pressure tester.

Figure(1-13):use dye

specifically made for

coolant when checking for

leaks using a black light.

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If water contains minerals, however, it can leave deposits in thecooling system that could prevent proper heat transfer. Because the

mineral content of most water is unknown, distilled water, which

has no minerals, is better to use. Although the cost of distilled

water must be considered, the amount of water required (usually

about 2 gallons [8 liters] or less of water) makes the expense minor

in comparison with the cost of radiator or cooling system failure.

Hydrometer Testing

Coolant can be checked using a coolant hydrometer. The hydrometer measures the density of the coolant. The higher the density, the more concentration of antifreeze in the

water.

Most coolant hydrometers read the freezing point and boiling point ofthe coolant.

Testing The Thermostat

There are three basic methods that can be used to check the operation of the

thermostat.1-Hot-water method ,2-Infrared pyrometer method,3-Scan tool

method.

Thermostat Replacement

An overheating engine may result from a faulty thermostat. An enginethat does not get warm enough always indicates a faulty thermostat.

To replace the thermostat, coolant will have to be drained from theradiator drain petcock to lower the coolant level below the thermostat.

It is not necessary to completely drain the system.The upper hose should be removed from the thermostat housing neck;

then the housing must be removed to expose the thermostat.

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