Cooling System

Cooling System-Definition, Types in Details, Advantages, Disadvantages, Necessity in Engine, PDF

Amrit Kumar Automobile Engineering 6 Comments

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Cooling System:


A typical 4 cylinder vehicle cruising along the highway at around 50 miles per hour,  will produce 4000 controlled explosions per minute inside the engine as the spark plugs ignite the fuel in each cylinder to propel the vehicle down the road. 

Obviously, these explosions produce an enormous amount of heat and, if not controlled, will destroy an engine in a matter of minutes. 

Controlling these high temperatures is the job of the cooling system.

Examples: Air and Water Cooling System (Thermosyphon and Thermostat  Cooling ).


  1. Air 
  2. Water 
  3. Steam and
  4. Liquid cooling system.

Air Cooling system:

This System is a simple type of cooling system used in scooter, motorcycle, and tractor.

In this system heat from the engine, the cylinder is directly dissipated to the atmosphere.

Necessity of Cooling System

The Basic Principle of this type of system is to allow a flow of current through the parts from which heat is to be dissipated, which depends upon the surface area of metal in contact rate of flow of air, a temperature difference between hot surface and air.

And Surface area of metal will be increased by providing the fins around the cylinder which is made of copper or steel.


Light in weight

No antifreeze is required

This system can be used where water scarcity is there

Simple in design

Require less space

No tapping up of water, etc.


More noise in operation.

The coefficient of heat transfer of air is less, hence less efficient in working.

Water cooling system:

This type is the most commonly used type of system.

In this system dissipation of heat is done by the circulation of water through the jackets around the cylinder and passes this hot water through the radiator where air absorbs heat from the water.

There are two types of water cooling system.

1.Thermosyphon and 2. Pump circulation system.

Thermosyphon System:

The pump is not fitted in this system.

Circulation of water is done due to the difference in densities between hot and cold water.

Circulation of water is due to natural convection.

A rate of cooling is low.

Nowadays it uses is limited because there must always a level of water is needed.

It is simple in construction and cheap.

Working of Thermosyphon system:

Thermosyphon cooling system operates on the principle of natural convec­tion.

Thermo-syphon water cooling system is based on the fact that water becomes light on heating and,

The top and bottom of the radiator are connected to the top and bottom of the cylinder water jacket respectively with the help of pipes.

The radiator is cooled by causing air to flow over it. Airflow is achieved by vehicle motion or a fan provided.

The heated water in cylinder water jacket becomes light and moves out of the upper connection pipe into the radiator and travels down from the upper tank to lower tank, rejecting heat as it travels.

This cooled water from the lower tank is passed into the cylinder water jacket and hence circulated again for the process.

An important limitation of this system is that the cooling depends only on temperature and is independent of engine speed.

Pump circulation system:

Circulation of water is done by providing a centrifugal pump.

Due to this pump, the rate of flow of water is more.

Here radiator may be fitted at any place convenient to the designer.

The pump is driven by a belt from a crankshaft.

Working of  Pump circulation system:

The water-cooling system has major components such as

water jackets, circulating pump, fan, thermostat, connecting pipes and hoses, radiator and radiator cap.

The direction of cooling water flow is upward from the cylinder head to the top tank of the

radiator, then down through the radiator core to the bottom tank.

From the bottom tank,

it moves through the lower radiator hose to the cylinder block water jackets and then through the water pump, which circulates the water.

Water enters the engine at the center of the inlet side of the pump.

The circulating pump is driven by a belt from the crankshaft.

As engine speed increases, the flow of coolant increases.

Parts of the Water Cooling System:

  1. Radiator
  2. Water Pump
  3. Fan
  4. Thermostat.

Steam Cooling System:

In this system, the radiator is in the form of the condenser.

Water from condenser enters the jacket and converted into the steam. 

Water flows from the top of the block and dissipates the heat and steam are condensed in condenser converts to water and used for next circulation.

Liquid cooling system:

Liquids other than the water if circulates around the cylinder is called the liquid system.

The liquid of higher boiling point such as Glycerine(Boiling point 195ºC) is used.

The higher boiling point increases the rate of dissipation of heat and reduces the size of the radiator and coolant required.

The necessity of Cooling system:

During Combustion of fuel, a tremendous amount of heat is produced.

Out of these heat produced,

25% of heat is used for mechanical work,

35% of heat is losses through the exhaust gases and

5% of heat losses through the Lubrication System.

Balance 35% heat Should be Dissipated by Cooling System.

An absence of this System causes seizure of piston, break down of lubricating oil, Overheating of valves and bearing, etc.

Volumetric efficiency and output power of engines reduce if the cylinder head temperature becomes high.

Hence this System is Necessary for the Vehicles.

An efficient system has a faster rate of cooling for the Hot engine and Slower rate of Cooling for Cold Engine.


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About the Author

Amrit Kumar


Amrit is a Co-founder of Learn Mechanical Portal (Previously owned ""). He completed his diploma in Mechanical Engineering from Acharya Polytechnic Bangalore and also completed his B-Tech from Delhi. Amrit is now preparing for Govt. exams. If you need help, you can ask him regarding any suggestions in the mechanical engineering field. He loves to meet new people.

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