How the engine cooling system works
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How the engine cooling system works

A car engine produces a lot of heat when it is running, and must be cooled continuously to avoid engine damage.

Generally this is done by circulating coolant liquid usually water mixed with an antifreeze solution through special cooling passages. Some engines are cooled by air flowing over finned cylinder casings.

How the coolant circulates

A typical water-cooling system with an engine-driven fan: note the bypass hose taking off hot coolant for the heater. The pressure cap on the expansion tank has a spring-loaded valve which opens above a certain pressure.

A water-cooled cooling system

A water-cooled engine block and cylinder head have interconnected coolant channels running through them. At the top of the cylinder head all the channels converge to a single outlet.

A pump, driven by a pulley and belt from the crankshaft, drives hot coolant out of the engine to the radiator, which is a form of heat exchanger.

Unwanted heat is passed from the radiator into the air stream, and the cooled liquid then returns to an inlet at the bottom of the block and flows back into the channels again.

Usually the pump sends coolant up through the engine and down through the radiator, taking advantage of the fact that hot water expands, becomes lighter and rises above cool water when heated. Its natural tendency is to flow upwards, and the pump assists circulation.

The radiator is linked to the engine by rubber hoses, and has a top and bottom tank connected by a core a bank of many fine tubes.

The tubes pass through holes in a stack of thin sheet-metal fins, so that the core has a very large surface area and can lose heat rapidly to the cooler air passing through it.

On older cars the tubes run vertically, but modern, low-fronted cars have crossflow radiators with tubes that run from side to side.

In an engine at its ordinary working temperature, the coolant is only just below normal boiling point.

The risk of boiling is avoided by increasing the pressure in the system, which raises the boiling point.

The extra pressure is limited by the radiator cap, which has a pressure valve in it. Excessive pressure opens the valve, and coolant flows out through an overflow pipe.

In a cooling system of this type there is a continual slight loss of coolant if the engine runs very hot. The system needs topping up from time to time.

Later cars have a sealed system in which any overflow goes into an expansion tank, from which it is sucked back into the engine when the remaining liquid cools.

How the fan helps

The radiator needs a constant flow of air through its core to cool it adequately. When the car is moving, this happens anyway; but when it is stationary a fan is used to help the airflow.

The fan may be driven by the engine, but unless the engine is working hard, it is not always needed while the car is moving, so the energy used in driving it wastes fuel.

To overcome this, some cars have a viscous coupling a fluid clutch worked by a temperature sensitive valve that uncouples the fan until the coolant temperature reaches a set point.

Other cars have an electric fan, also switched on and off by a temperature sensor.

To let the engine warm up quickly, the radiator is closed off by a thermostat, usually sited above the pump. The thermostat has a valve worked by a chamber filled with wax.

When the engine warms up, the wax melts, expands and pushes the valve open, allowing coolant to flow through the radiator.

When the engine stops and cools, the valve closes again.

Water expands when it freezes, and if the water in an engine freezes it can burst the block or radiator. So antifreeze usually ethylene glycol is added to the water to lower its freezing point to a safe level.

Antifreeze should not be drained each summer; it can normally be left in for two or three years.

Air-cooled engine cooling systems

In an air-cooled engine, the block and cylinder head are made with deep fins on the outside.

Fins on an air-cooled cylinder are wider at the top, where most heat is generated.

Horizontal air-cooled engines have cooling ducts to the fins.

Air-cooling through fins

Fins on an air-cooled cylinder are wider at the top, where most heat is generated.

Horizontal air-cooled engines have cooling ducts to the fins.

Fins on an air-cooled cylinder are wider at the top, where most heat is generated.

Water-valve heating system

In a heater worked by a water valve, all the air goes through the matrix. The matrix temperature is controlled by regulating the amount of hot water going through it.

Frequently a duct runs all around the fins, and an engine-driven fan blows air through the duct to take heat away from the fins.

A temperature-sensitive valve controls the amount of air being pushed around by the fan, and keeps the temperature constant even on cold days.

Cooling the oil

Air-cooled engines and high-performance water-cooled engines may have in addition to a water radiator a small extra radiator, through which engine oil flows to be cooled.

Remember, the cooling system in your car is vital and can save you a lot of time on road if taken care of well.
Vehicles burn if over heating occurs, vehicles can fail to start or stop abruptly if the cooling system is faulty.

Visit Daks Toyota if you ever suspect your cooler having a problem. How do you know if it has a problem


You comment will be published within 24 hours.


  • Saara Caitrona
    July 5, 2017, 12:08 pm REPLY

    A vehicle engine deal with lot of heat when running and it needs to cool down, otherwise the engine cannot resist the excessive heat from both outside and inside of the car. A water cooled engine block and cylinder heat have interconnected coolant channels running on them. The radiator needs a constant flow of air to cool it adequately. To let the engine warm up quickly, the radiator is closed off and water freezes like antifreeze which should not be drained each summer. Horizontal air cooled engine have cooling ducts to fins. Remember, the cooling system in your car can save lot of time in road if taken care well. A faulty cooling system can cause real trouble in car.

  • Hendrix Odilian
    November 15, 2017, 12:20 pm REPLY

    Engine is the main functional part in an automobile. So knowing its importance, as a car owner you need to keep it in well maintained. Avoid overheating to it you can increase its longevity by keeping cool it inside. According to the types of cooling system that your car need you must cool it by providing water or air as required.This reduces the overheating of the engine and keep the engine part in tip-notch condition.

  • Autorepairsdirect
    September 14, 2020, 4:36 am REPLY

    Every car is required car engine cooling system because when car will run that time car engine is to heat and it is so harmful for engine that is the main purpose. We need to use car cooling system.

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