Engine Cooling System by Nazmul Huda

2. A system, which controls the engine temperature, is known as a
cooling system.
Purpose of Cooling System:
 To remove the excessive heat from the engine to avoid
damaged of the engine components.
 Too much cooling is also not desirable because it reduces the
thermal efficiency.
 The engine will perform best in the desired operating
temperature.
Cooling System

3. Types of cooling system
 Air cooling system
 Water cooling system

4. Air-cooling System
 Air cooled system is generally used in small engines such as
15-20 kW and in aero plane engines.
 In this system fins or extended surfaces are provided on the
cylinder walls, cylinder head, etc.
 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.

5. Factors affect cooling efficiency
The amount of heat dissipated to air depends
upon :
1) Velocity and amount of air flowing
through the fins.
2) Fin surface area.
3) Thermal conductivity of metal used for
fins
4) The temperature of the fins and the
cooling air.

6. Advantages of Air Cooling
 System is light because radiator/pump is absent.
 There are no leakages.
 Coolant and antifreeze solutions are not required.
 Can be used in cold climates, where if water is used it may
freeze.
 It is cheaper to manufacture.
 It needs less care and maintenance.

7. Disadvantages of Air Cooling
 Comparatively it is less efficient.
 It is used in aero planes and motorcycle engines where the
engines are exposed to air directly.

8. Water-cooling System
 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
vehicle.
 The cooled water is again recirculated through the water jackets.

9. Types of water-cooling system
1. Direct or non-return water-cooling system
2. Open Hopper water-cooling system
3. Thermo-siphon water-cooling system
4. Pump or forced circulation water-cooling system

10.  This is suitable for large installations and where plenty of water
is available.
 The water from a storage tank is directly supplied to the engine
cylinder.
 The hot water is not cooled for reuse but simply discharges.
 The low H.P. engine, coupled with the irrigation pump is an
example.
Direct or Non-Return Water
Cooling System

11.  This system works on the principle that hot water being lighter rises
up and the cold water being heavier goes down.
 In this system the radiator is placed at a higher level than the engine
for the easy flow of water towards the engine.
 Heat is conducted to the water jackets from where it is taken away due
to convection by the circulating water. As the water jacket becomes
hot, it rises to the top of the radiator.
 Cold water from the radiator takes the place of the rising hot water and
in this way a circulation of water is set up the system. This helps in
keeping the engine at working temperature.
Thermo Siphon water cooling System

12. Thermo Siphon System

13. Thermo Siphon water cooling System

14. Advantages of Thermo Siphon water cooling System
 Construction is comparatively cheap because no water pump is
required.
 Reliable as there are no moving parts.
 Circulation of water depends on engine temperature.
 Dis-Advantages
 Rate of circulation is too slow.
 Circulation commences only when there is a marked difference
in temperature.
 Circulation stops as the level of water falls below the top of the
delivery pipe of the radiator. For these reasons this system has
become obsolete and is no more in use.

15.  This also works on the same principle as the thermo-siphone
system.
 In this there is a hopper on a jacket containing water, which
surrounds the engine cylinder.
 In this system, as soon as water starts boiling, it is replaced by
cold water.
 An engine fitted with this system cannot run for several hours
without it being refilled with water.
Hopper Water Cooling System

16.  This system is similar in construction to the thermo-siphone system
except that it makes use of a centrifugal pump to circulate the water
throughout the water jackets and radiator.
 The water flows from the lower portion of the radiator to the water
jacket of the engine through the centrifugal pump.
 After the circulation water comes back to the radiator, it loses its heat
by the process of radiation. This system is employed in cars, trucks,
tractors, etc.
Pump or forced Circulation water cooling System

17. Pump or forced Circulation System

18. Working principle of Pump or forced
Circulation water cooling system.

19. Components of water cooling system
 Radiator
 Water pump
 Thermostat
 Radiator pressure cap
 Expansion tank
 Radiator fan
 Water temperature indicator

20. Radiator
 The radiator is basically a heat
exchanger, transferring heat from the
engine to the air passing through it.
 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.

21. Water Pump
 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 belt.

22.  The pumps are centrifugal-type pumps
with a rotating impeller to move the
coolant.
 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 block.

23. Thermostat
 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.

24. 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 the radiator.

25. Radiator Fan
 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.

26.  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 the engine.
 Thus, belt-driven fans always draw air through the radiator
from the rear.

27. Advantages of Water-Cooled System
 Uniform cooling of cylinder, cylinder head and valves.
 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.

28. Disadvantages of Water-Cooled System
 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.