Air cooling, liquid cooling and oil cooling explained


An automotive engine is a machine that converts heat energy into mechanical energy. But, It is impossible to completely convert the heat generated in the engine cylinder into energy. 

This causes the heat inside the engine to increase. In addition, the friction between the moving parts of the engine increases the temperature. Excessive heat can damage the engine parts, shortening the life of the engine.

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What is an engine cooling system?

For the engine to work properly, it is essential to maintain an operating temperature. Normally, an engine works properly at about 90 degrees Celcius. This temperature range is called the engine operating temperature. The function of the cooling system is to maintain the engine operating temperature. 

The two major types of cooling systems used in an automobile are the air cooling system and the liquid cooling system.


Air cooling system

Generally, the air cooling system is used on bikes below 200 cc. This is a simple system where the heat of the engine is reduced with the help of atmospheric air. This allows maximum air circulation outside the engine cylinder.

The surface area needs to be increased for more air circulation. For this, fins are provided on the engine's outer surface. Thus the surface area increases, thereby increasing air circulation and cooling the engine. 

However, in scooters, the engine is cooled with the help of a fan. Here normal air cooling has limitations because the engine is covered by the body parts. This is called forced air cooling.


Advantages of air cooling system

  • This is a simple system
  • Lightweight
  • Maintenance is not required
  • No need for coolant


Disadvantages of air cooling system

  • It is not possible to use in high-capacity engines.
  • It is impossible to use in cars because the engine is placed inside the bonnet. Not only, but the car also uses a multi-cylinder engine, so an air cooling system is not practical.
  • It does not provide uniform cooling.


Oil cooling system

This is not a primary cooling system. The oil cooling system is used as a supplementary system of air cooling. We can also see this system in some liquid-cooled engines.

We know that engine oil is used in engines for lubrication.  Not only lubrication, but the engine oil absorbs a certain percentage of engine heat also. That is, the engine oil plays a role in cooling as its secondary function. 

So through oil cooling system, try to improve its efficiency. For that, allows the engine oil to pass through a radiator. Thus the heat absorbed by the oil is removed.

An oil pump pumps the engine oil to the radiator from the oil sump. The hot oil pass through the aluminum tubes provided in the radiator thus cooling the oil. The cold oil then enters the engine through an oil filter.

This is the process that takes place in an oil-cooled engine. If use the combination of air cooling and oil cooling, will improve the efficiency of the system.


Liquid cooling system


Liquid cooling is one of the most efficient cooling systems. Water is the main ingredient in this system, the mixture of distilled water and some kind of chemicals, This is known as coolant. 

A radiator, thermostat valve, water pump, and expansion tank are the components of this system. The coolant flows through the water jackets(gallery) provided on the cylinder side and the engine head areas, which cools the engine.

The water pump pumps the coolant to the water gallery, and the flow of coolant through the gallery cools the engine by absorbing engine heat. After that, the hot coolant flows near to the thermostat valve from the engine. 

If the coolant is not overheated (not above engine operating temperature ), the coolant flows through the bypass to the water pump, repeating the process.

If the coolant from the engine is overheated ( above normal engine operating temperature level), the thermostat valve opens and the coolant flows to the radiator. Coolant flows through the narrow aluminum tube provided in the radiator and cools and flows to the water pump.

The cap provided on the upper tank of the radiator allows the coolant to maintain a specific pressure level. It does not allow the coolant to vaporize. If there is an overpressure, the radiator cap allows the coolant to flow to the expansion tank. For that purpose, there is a valve provided in the radiator cap. 

If the pressure decreases, there creates a vacuum and sucks the coolant from the expansion tank to the radiator. This helps to maintain a specific pressure all the time and does not allow the creation of air in the system. To maintain the pressure inside the expansion tank provides a hole at the top portion of it.

And also provides a fan near the radiator to improve the efficiency of the system. If the vehicle is moving slowly or climbing an ascent, the airflow near the radiator reduces. In these situations, a radiator fan helps provide air circulation.


Additionally, uses temperature sensors to sense the coolant temperature. Many vehicles use heat exchanges to exchange the oil temperature for the coolant. This helps to cool the engine and also helps to maintain the properties of the engine oil.

Advantages of liquid cooling

  • This is an efficient cooling system, compared to others.
  • It is possible to use in high-capacity engines


Disadvantages of liquid cooling

  • Maintenance is a  bit difficult, it has several components, The problems with the radiator cap, problems with the radiator cap, thermostat valve, and fan cause the failure of the water cooling system. 
  • Need to change coolant at regular interval
  • Energy loss, Radiator fan, and water pump are using energy from the engine to work.

The cooling system is an important system for every automobile to work properly. If the engine gets overheated, it will make problems for the engine. Engine overheating leads to detonation, and pre-ignition and may cause the engine to cease. So, it is important to maintain the cooling system properly.

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