1. ME390 Automotive Mechanics
2. Engine Cooling Systems

2. Topics Covered
Need for cooling
Types
Air cooling
Liquid cooling

3. Need for Engine cooling
High temperatures reached during combustion (2000 – 2500oC in CI engines)
Over heating of parts result in engine breakdown

4. Need for Engine cooling
Effects of inadequate cooling
Evaporation of lubricating oil
Setting up of thermal stresses
Sticking of piston rings in the cylinder due to carbonization of the oil
Burning of piston crown
Burning and warping of exhaust valves
Reduction in volumetric efficiency i.e. reduced weight of charge retained in the cylinder

5. Need for Engine cooling
Result of excessive cooling
Reduction in thermal efficiency
Increased corrosion
Reduced mechanical efficiency
Improper vaporization of fuel.
Optimum cooling is required for most effective operation of the engine.
Hence the cooling system removes excess heat from the engine to avoid over heating and subsequent problems associated with it.

6. Types of cooling
Direct or Air cooling
Indirect or liquid cooling

7. Air cooling
Large quantity of air is circulated around the hot engine components
Air flows either due to vehicle movement or due to fan or blower in case where the engine is enclosed.
Air flows through the spaces between fins provided around the cylinder and cylinder head.
Fins around the cylinder and
cylinder head facilitates air
cooling

8. Air cooling
Blower cooling of an opposed engine (VW beetle)

9. Air cooling
Factors that determine heat dissipating capacity in air cooling
Fin shape, size and spacing
Velocity and amount of air flowing over the fins
Temperature of the cylinder, fins and cooling air

10. Air cooling Merits Demerits Less complex design Less engine weight
Cheaper to manufacture
Compact
No risk of coolant frost
Easier engine maintenance
Demerits
Greater mechanical noise
Not suitable for multi-cylinder engine

11. Liquid cooling Most widely used owing to better heat transfer.
Coolants used
Water
Ethylene glycol
Preston
Glycerine
Water is most widely used due to its easy availability and high heat transfer capacity.

12. Liquid cooling
Parts of liquid cooling system (pump circulation system)
Water jackets
Water pump
Thermostat
Radiator
Fan

13. Liquid cooling Water Jackets
Cooling water jackets are provided around the cylinder, cylinder head, valve seats and any hot parts which are to be cooled. Heat generated in the engine cylinder, conducted through the cylinder walls to the jackets. The water flowing through the jackets absorbs this heat and gets hot. This hot water will then be cooled in the radiator

14. Liquid cooling Water Pump
It is used to pump the circulating water. Impeller type pump will be mounted at the front end.
The pump is driven by means of engine output shaft only through belts. When it is driven water will be pumped.

15. Liquid cooling Thermostat valve
It controls the flow of coolant to the engine. It is a valve which prevents flow of water from the engine to radiator, so that engine readily reaches to its maximum efficient operating temperature. After attaining maximum efficient operating temperature, it automatically begins functioning. Generally, it prevents the water below 70°C.
It contains a bronze bellow containing liquid alcohol. Bellow is connected to the butterfly valve disc through the link. When the temperature of water increases, the liquid alcohol evaporates and the bellow expands and in turn opens the butterfly valve, and allows hot water to the radiator, where it is cooled.

16. Liquid cooling Radiator
It mainly consists of an upper tank and lower tank and between them is a core. The upper tank is connected to the water outlets from the engines jackets by a hose pipe and the lover tank is connect to the jacket inlet through water pump by means of hose pipes.
When the water is flowing down through the radiator core, it is cooled partially by the fan which blows air and partially by the air flow developed by the forward motion of the vehicle. It is to be noted that radiators are generally made out of copper and brass and their joints are made by soldering.

17. Liquid cooling
Fan
It is driven by the engine output shaft through same belt that drives the pump. It is provided behind the radiator and it blows air over the radiator for cooling purpose.

18. Liquid cooling (Pump circulation system)

19. Liquid cooling (Pump circulation system)

20. Liquid cooling Thermo syphon system
Water jackets in
Cylinder block and
Cylinder head
Radiator
Hot water moving up
to radiator top header
Cold water moving to fill the
coolant space
Fan
Thermo syphon system
Works on the principle of natural convection
Coolant is at rest when the engine is cold
During engine operation the coolant gets heated and moves up to top header of the radiator
Cold water from lower part of radiator flows and fills up the coolant space in cylinder head and cylinder block
Hot water flows down through the radiator and gets cooled by air flow

21. Liquid cooling Thermo syphon system
For successful operation the pipes should be free/clear and large.
Jackets should be placed as low as possible compared to the radiator
Requires large radiator, large amount of water.
Excessive temperature difference is necessary for proper circulation
Prevents the engine from running too cold
Simple in construction and operation

22. Liquid cooling Problems Air in the cooling system
Freezing of the coolant
Deposit formation in the cooling system