What is an air-cooled car engine?

This blog will answer the question, ‘What is an air-cooled car engine?’, and cover the topic, how is an air-cooled engine different from a water-cooled engine.

What is an air-cooled car engine?

An air-cooled engine uses air to cool off heated engine components. They make use of a mechanism that blows cool air over a set of fins protruding out of the components. These fins help in dissipating heat.

This system allows air to be carried away by the air flowing over and around the cylinder. Gasoline engines require more air than diesel engines to cool their components and turbo-charged diesel engines require less cooling air than the naturally aspirated diesel engines.

How is an air-cooled engine different from a water-cooled engine?

The composition and structure of air and water-cooled engines have been discussed along with their advantages and disadvantages.

Air-cooled engines

Air-cooled engines use fins cast on the cylinder head and cylinder barrel which provide an additional conductive and radiative surface. The fins are arranged at right angles to the cylinder axis.

The number and dimensions should be adequate to take care of the surplus heat dissipation.

The fin surface area which is a function of fin height and spacing decreases down the cylinder compared to the fin surface area in the cylinder head comprising the exhaust valve space and spaces between the valves.

Effective valve cooling requires methods of conducting the heat from the valve head to the cylinder, imposed guides, and the metal along with the lower part of the valve stem operating under cooler air conditions.

In order to enhance the conductivity of the exhaust valve, the practice of making the valve stem and even the heads hollow is becoming popular in large engines.

The hollow stem is filled with sodium, which melts at 97 degrees Celsius, and boils at 880 degrees celsius. Thus at valve operating temperatures, the valve is filled with conducting material.

Applications of an air-cooled system

Air-cooled engines are used in small aircraft engines where the application of these gives extreme importance to weight. They are also used in industrial and agricultural engines where there can be a strong objection to the use of water as a coolant medium.

Advantages of an air-cooled system

These are the following advantages of an air-cooled car engine:

  • The design of the engine becomes simpler as there is no involvement of water jackets.
  • The cylinder can be of identical dimensions and individually detachable and therefore, cheaper to renew in case of accidents, etc.
  • The absence of cooling pipes, radiators, etc, makes the cooling system simpler.
  • There is no danger of coolant leakage
  • The engine is not subjected to freezing troubles as there is no involvement of water.
  • The weight per BP of the air-cooled engine is less than that of the water-cooled engine.
  • In this case, an engine is rather a self-contained unit as it requires no external components like the radiator, headers, tank, etc.
  • Air-cooled engines are easier to install
  • Air-cooled systems are much easier to control than water-cooled systems

Disadvantages of an air-cooled system

These are the following disadvantages or drawbacks to having an air-cooled.

  • Noisy movement
  • The cooling pattern is non-uniform
  • The car output from the engine is less than the liquid-cooled engine
  • It is cheap to conduct maintenance
  • The useful compression ratio is smaller
  • Lower volumetric efficiency

Water-cooled engines

In this method of cooling engines, the cylinder walls and heads are provided with jackets through which the cooling liquid can circulate. The heat is transferred from cylinder walls to the liquid by convection and conduction.

The liquid becomes heated in its passage through the jackets and is itself cooled by means of an air-cooled radiator system. The heat from the liquid in turn is transferred to the air.

The coolant to be employed in liquid cooling systems should possess the following characteristics:

  • Low freezing temperature
  • A high boiling point
  • A large latent heat of vaporization
  • Non-corrosive
  • Easily and cheaply available

Water possesses these properties and is mostly employed in liquid-cooling systems.

Anti-freeze solution plays an important role in water-cooling systems. When the engine is kept in unheated areas and is not being operated, with the temperature below freezing, the water in the cooling system is liable to get frozen.

The solid mass of water due to expansion may cause fracture of the cylinder block, water jackets, and pipes. The radiator may also be damaged. 

Anti-freeze mixtures or solutions are added to water in extreme winter seasons to lower its freezing temperatures below the danger point. 

Most commonly used anti-freeze materials include:

  • Denatured alcohol
  • Wood alcohol
  • Glycerine
  • Kerosene
  • Sugar solution
  • Calcium or magnesium chloride
  • Ethylene glycol and propylene glycol

Water-cooled engines use the following methods to circulate water around the cylinder and cylinder heads:

  • Thermo-syphon cooling
  • Forced or pump cooling
  • Cooling with the thermostatic regulator
  • Pressurized water cooling
  • Evaporative cooling

Advantages of water-cooled engines

These are the following advantages of water-cooled engines:

  • The compact design of the engine with an appreciably smaller frontal area is possible.
  • The fuel consumption of high compression liquid-cooled engines is rather lower than for air-cooled ones.
  • More even cooling of cylinder barrels and heads due to jacketing makes it easier to reduce the cylinder head and valve seating temperature.
  • In the case of the water-cooled engine, installation is not necessary at the front of the mobile vehicles, aircraft, etc.

Disadvantages of water-cooled engines

These are the following disadvantages of water-cooled engines:

  • Dependent on the supply of water for circulation in the jacket
  • Power absorbed by the pump for water circulation is considerably higher than that for cooling fans
  • In the event of failure of the cooling system serious damage may be caused to the engine
  • Cost of the system is considerably high
  • The performance of the system is weather dependent

Research has shown the different cars that run on air-cooled engines.


This blog post addressed the question, ‘What is an air-cooled car engine?’

We came to understand the working principle of an air-cooled car engine and also came across a descriptive comparison between an air-cooled engine and a water-cooled engine. Please feel free to comment on the content or ask any questions in the comments section below.

Frequently Asked Questions (FAQs): What is an air-cooled car engine?

What is the purpose of air-cooled engine?

Air-cooled engines are used to cool engines by using the air that the car comes into contact with during motion. To make this possible, they deploy fins that have a large surface area to allow air to pass through and hit the engine as much as possible to cool it down.

Are air-cooled engines good?

Air-cooled engines have a big advantage over water-cooled engines as their cooling medium involves no liquid usage, which omits the problem of coolant leakage, and additionally, they are more lightweight in build.

Do air-cooled engines overheat in traffic?

Air-cooled engines make use of the air to hit the engine and cool it down. Therefore, the vehicle being stationary heats the engine up due to the lack of flowing air while being stuck in traffic.