Chapter 2 –
MUHAMMAD HILMI BIN ZAID
The topic covers basic theoretical
knowledge on engine cooling systems.
Areas involving type, function and
working principles of cooling systems and
its components. Coolant or anti-freeze is
also discussed in this topic.
Understand function, construction and operation of
cooling system and its components
Describe types of cooling system:
Explain the function, construction and operation of
water cooling system and its components:
Radiator pressure cap
Water temperature indicator
Understand different types of coolants/anti-
Explain various types of coolants/anti-
Organic Acid Technology
Hybrid Organic Acid Technology
amount of heat.
Most of this heat is
chamber can run
as high as 1,000°F
This heat can
engine and must
Purpose of Cooling System
Purpose - To remove the
excessive heat from the
engine to avoid
components in the
Too much cooling is also
not desirable because it
reduces the thermal
The engine will perform
best in the desired
TYPES OF COOLING SYSTEM
Air cooled system is generally used in small
engines such as 15-20 kW and in aero plane
In this system fins or extended surfaces are
provided on the cylinder walls, cylinder head,
Heat generated due to combustion in the
engine cylinder will be conducted to the fins
and when the air flows over the fins, heat will
be dissipated to air.
Factors affect cooling
The amount of heat
dissipated to air depends
1) Amount of air flowing
through the fins.
2) Fin surface area.
3) Thermal conductivity of
metal used for fins
System is light because radiator/pump is
There are no leakages.
Coolant and antifreeze solutions are not
Can be used in cold climates, where if
water is used it may freeze.
Comparatively it is less efficient.
It is used in aero planes and motorcycle
engines where the engines are exposed
to air directly.
In this method, cooling water jackets are
provided around the cylinder, cylinder head,
valve seats etc.
The water when circulated through the
jackets, it absorbs heat of combustion.
This hot water will then be cooling in the
radiator partially by a fan and partially by the
flow developed by the forward motion of the
The cooled water is again recirculated
through the water jackets.
Types of water-cooled system
Thermo Siphon System
In this system the circulation of water is due
to difference in temperature (i.e. difference
in densities) of water. So in this system pump
is not required but water is circulated
because of density difference only.
Pump Circulation System
In this system circulation of water is
obtained by a pump. This pump is driven by
engine output shaft through belts.
Working principle of water-
Heat is removed
from around the
chambers by a
A pump moves
flows to the top
of the radiator
and loses heat
as it flows down
Ram air and the
airflow from the
the radiator and
the radiator and
enters the water
pump then its
Radiator pressure cap
Water temperature indicator
The radiator is basically a heat
exchanger, transferring heat from
the engine to the air passing
The radiator itself is a series of
tubes and fins (collectively called
the core) that expose the
coolant’s heat to as much
surface area as possible.
Attached to the sides or top and bottom of the
core are plastic or aluminum tanks.
One tank holds hot coolant and the other holds
the cooled coolant.
Cores are normally comprised of flattened
aluminum tubes surrounded by thin aluminum fins.
The fins conduct the heat from the tubes to the air
flowing through the radiator.
Most radiators have draincock or plugs near the
Coolant is added at the radiator cap or the
Design of radiators
Radiators are normally based on one of
two designs: cross flow or down flow.
In a cross-flow radiator, coolant enters on
one side, travels through tubes, and
collects on the opposite side.
In a down-flow radiator, coolant enters
the top of the radiator and is drawn
downward by gravity.
The heart of the cooling
system is the water pump.
Its job is to move the coolant
through the system.
Typically the water pump is
driven by the crankshaft
through pulleys and a drive
The pumps are centrifugal-
type pumps with a rotating
impeller to move the
The shaft is mounted in the
water pump housing and
rotates on bearings.
The pump has a seal to
keep the coolant from
passing through it.
The inlet of the pump
connects to the lower
radiator hose, and its outlet
connects to the engine
A thermostat is a temperature-responsive
coolant flow control valve.
It controls the temperature and amount
of coolant entering the radiator.
Most thermostats are located on the top
and front of an engine.
How it works?
While the engine is cold, the thermostat
remains closed, allowing coolant to only
circulate in the engine.
This allows the engine to uniformly warm up.
When the coolant reaches a specified
temperature, the thermostat begins to open
and allows coolant to flow to the radiator.
The hotter the coolant gets, the more the
thermostat opens, sending more coolant to
Thermostat Closed Thermostat Open
When engine is cold When engine reaches the
The thermostat permits fast engine warm-
Slow warm-up causes condensation in the
crankcase, which can cause the
formation of sludge.
Radiator Pressure Cap
Radiator caps keep the coolant from
splashing out of the radiator.
They also keep the coolant’s temperature
within a desired range by keeping the
coolant pressurized to a specified level.
The pressure raises the boiling point of the
This allows the coolant to reach higher-
than-normal temperatures without boiling.
This also allows the coolant to absorb
more heat from the engine and more
heat to transfer from the radiator core to
This is due to a basic law of nature that
states that the greater the heat
difference is between two objects, the
faster the heat of the hotter object will
move to the cooler object.
The pressure in the system is regulated by
a pressure relief or vent valve in the
When the pressure reaches the pressure rating of the
cap, it pushes up on the spring in the pressure relief
This opens the valve and allows excess pressure to exit
When enough pressure has been released, to drop
system pressure below the cap’s rating, the spring will
close the pressure relief valve.
All late-model cooling systems have an
expansion or recovery tank.
Cooling systems with expansion tanks are
called closed-cooling systems.
They are designed to catch and hold any
coolant that passes through the pressure
How it works?
inside the pressure
cap opens and the
coolant in the
expansion tank is
drawn back into
the cooling system.
The coolant passes
to an expansion
tank. When the
engine is shut
down, the coolant
begins to shrink.
As the engine
warms up, the
pressure cap to
The efficiency of the cooling system
depends on the amount of heat that can
be removed from the system and
transferred to the air.
At high speeds, the ram air through the
radiator should be sufficient/enough to
maintain proper cooling.
At low speeds and idle, the system needs
additional air. This air is delivered by a fan.
The fan may be driven by the engine, via
a belt, or driven by an electric motor.
A belt-driven fan is bolted to a pulley on
the water pump and turns constantly with
Thus, belt-driven fans always draw air
through the radiator from the rear.
Problem of belt-driven fan
Fan air is usually only necessary at idle
and low-speed operation.
Horsepower is required to turn the fan. The
operation of a cooling fan reduces the
available horsepower to the drive wheels
and the fuel economy of the vehicle.
Fans are also very noisy at high speeds,
adding to driver fatigue and total vehicle
To eliminate this power waste during times
when fan operation is not needed, many of
today’s belt-driven fans operate only when
the engine and radiator heat up.
This is accomplished by a fan clutch.
When the engine and fan clutch are cold, the
fan moves independently from the clutch
and moves little air.
In most cases, the clutch slips at high speeds;
therefore, it is not turning at full engine speed
Water Temperature Indicator
Coolant temperature indicators alert the
driver of an overheating condition.
These indicators are a temperature
gauge and/or a warning light.
A temperature sensor is threaded into a
bore in a water jacket.
Engine coolant is a mixture of water and
Water alone has a boiling point of 100°C and a
freezing point of 0°C at sea level.
Engine coolant has a higher boiling temperature
and a lower freezing point than water.
The exact boiling or freezing temperatures
depend on the mixture.
The typical recommended mixture is a 50/50
solution of water and antifreeze/coolant.
This is the most commonly used
It is green in color and provides good
protection regardless of climate, but it is
Should be handled carefully and
disposed of properly.
Sweet tasting (accidental ingestion or as
a murder weapon)
This type has the same basic characteristics
as ethylene glycol-based coolant but is not
Less harmful to animals and children. (non-
Used when ethylene-glycol is inappropriate
such as in food processing system or water
pipes system in homes.
Propylene glycol-based coolants should not
be mixed with ethylene glycol.
Organic acid technology
This coolant is also environmentally
friendly and contains zero phosphates or
This orange coolant is often referred to by
a brand name “DEX-COOL” and is used in
all late-model GM vehicles.
Extended service life of 240 000 km.
Hybrid organic acid
This is similar to OAT coolant but has been
enhanced with additives (silicates or
phosphates) that make the coolant less
abrasive to water pumps
Advantages of Water-Cooled
Uniform cooling of cylinder, cylinder head
Specific fuel consumption of engine improves
by using water cooling system.
If we employ water cooling system, then
engine need not be provided at the front end
of moving vehicle.
Engine is less noisy as compared with air
cooled engines, as it has water for damping
Disadvantages of Water-
It depends upon the supply of water.
The water pump which circulates water
absorbs considerable power.
If the water cooling system fails then it will
result in severe damage of engine.
The water cooling system is high cost as it
has more number of parts.
Also it requires more maintenance and
care for its parts.
Why is cooling necessary for IC engine?
Explain in brief the methods of cooling of
Differentiate between air cooling system
and water cooling system.
What is the purpose of the fins in an air-
Explain the function of thermostat?