Cooling System

Engine Cooling, or Cooling System is on two types:

  • Air Cooling System
  • Water Cooling System

Air Cooling System

Air cooling system, with this type of cooling system the heat which is conducted to the outer parts of the engine, is radiated away by the stream of air which is provided by the fan or which is obtained from the atmosphere. In order to have efficient cooling by means of air, the contact area is increased by providing fins around the cylinder and cylinder head, the hot spots of the engine.

Water Cooling System

Water cooling system, serves two purposes in the working of an engine:

  • It takes away excessive heat generated in the engine and saves it from overheating.
  • It keeps the engine at the working temperature for the efficient and economical working.

This system is of two types, i.e.,

  1. Thermo Syphon Water Cooling System.
  2. Impeller Pump Water Cooling System.

Thermo Syphon Water Cooling System

The thermo syphon water cooling system works on the principle that hot water being lighter rises up and the cold water being heavier goes down.

In the water cooling system, the stream of cold wter runs around all those spaces (cylinder, combustion chamber, valve ports, etc.), which are subject to more heat. The pockets through which water flows in an engine are known as “Water Jackets.”

Following are the main parts:

  1. Radiator. A device which cools down hot water.
  2. Water Hoses. Which provide connections between engine and radiator.
  3. Water Jackets. Water pockets through which water flows in the engine.
  4. Fan. To draw fresh air through the radiator and throw on the outer portions of the engine in order to increase efficiency of the water cooling system.
  5. Temperature Gauge. A gauge to record the temperature of water in the engine.


Water is filled into the system through the radiator filler neck. Radiator, in the thermosyphon system, is placed at a higher level than 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 water becomes hot it rises up towards the engine water outlet and next to the top tank of radiator. Gold water from radiator takes the place of rising up hot water and this way a circulation of water is set up in the system, which helps in keeping engine at the working temperature.

Impeller Pump Water Cooling System

Impeller pump water cooling system is, due to more reliability of the system, more common in motorcycles. It comprises of the following main parts:

  1. Radiator and connections,
  2. Water Pump,
  3. Water Jackets,
  4. Fan,
  5. Overflow Tank,
  6. Thermostat Valve,
  7. Temperature Gauge,
  8. Radiator Shutters.


There are three types of radiators for the Impeller Pump Water Cooling System:

  1. Gilled tube Radiator.
  2. Tubular Radiator
  3. Honey Comb or Cellular Radiator.
Gilled Tube Radiator

The gilled tube radiator consists of three main parts, i.e.,:

  • Upper Tank
  • Bottom Tank
  • Tubes

Both the upper and bottom tanks are connected with the tubes which run vertically from top to bottom. Separate copper fins are provided around the individual tubes.


Hot water from the upper tank which comes from the engine flows downwards through the tubes. As water flows from the upper tank to the bottom tank, the heat contained in the hot water is conducted to the copper fins provided around the tubes. Atmospheric air which is drawn in by the fan comes in contact with the radiator tubes and fins and the heat conducted by them is radiated away.

Tubular Radiator

The only difference between gilled tube radiator and tubular one being that there are no separate fins for the individual tubes but through thin fine copper sheets which run horizontally, pass the radiator vertical tubes.

Honey Comb or Cellular Radiator

A cellular radiator consists of a large number of individual air cells which are surrounded by water. The construction of this type of radiator is like the bee hive that is why it is known as Honey Comb Radiator. In a tubular radiator, if one tube is clogged the cooling effect of the entire tube is lost. In the cellular radiator the clogging of any passage results in loss of a small part of the total cooling surface.


The fan is driven on most modern motorcycles by an electro motor. The fan is fitted between the engine and the radiator. It serves two purposes in the cooling system of the engine.

  • The fan ensures regular flow of atmospheric air through the radiator and thus increases the efficiency of radiator in cooling down hot water.
  • The fan throws fresh air over the outer surface of engine parts and thus is increases the effiency of the whole cooling system of the engine.
Water Pump

The water pump which is of the impeller type, consists of the following parts:

  • Body,
  • Impeller (Rotor),
  • Shaft, bearing and seal.

The pump is driven by a electro motor. The impeller pump drives water towards the water jackets setting up a regular circulation of water in the system.

Thermostat Valve

The thermostat valve is a kind of check valve which opens and closes with the effect of temperature. It is fitted in the water outlet of the engine water cooling system. It helps in raising the temperature of coolant, during cold seasons, since the valve begins to open at a preset temperature, and unless the temperature of the engine water reaches this degree, this valve does not provide passage for the water towards the radiator.

The valve is of poppet type, which is fitted with bellows filled with liquid, such as acetone, alcohol and is contained in a cage. As the temperature affects thin metal bellows, the liquid inside evaporates which expands the bellows and tends the valve to lift of the seat. When the temperature falls below the set temperature the valve is closed due to the squeezing of bellows.

Overflow Tank

The overflow tank is a small tank which collects the coolant after it flows out of the radiator in the form of steam through the overflow pipe. Overflow tank is necessary because it saves the expending hot water, which is needed, and can flow back to the cooling system when the engine cools down.

cooling.txt · Last modified: 2014/04/15 17:50 (external edit)
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