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How Does a Cooling System Work?

By: Kevin Watson MSc - Updated: 30 Sep 2012 | comments*Discuss
Cooling System Heat Radiator Coolant

In an internal combustion engine, a blend of fuel and air causes a series of mini explosions. An engine converts these explosions into power. But as part of the process, the temperature of the engine can rise dramatically.

If left alone, such heat destroys the engine. Every vehicle therefore needs a cooling system. This dissipates and controls the heat, thereby ensuring that an engine performs safely and well.


A cooling system is fairly sophisticated. Its major parts are coolant, a pump, a thermostat, a radiator, a cooling fan, hoses, and drive belts. These combine to keep the temperature of an engine at a level that maximises its efficiency and keeps emissions to a minimum.


An engine’s coolant is a mix of ethylene glycol and water. The result is a liquid with a lower freezing point and a higher boiling point than water. The coolant can therefore sustain a greater range of temperature without turning to ice or vapour.

A cooling system is also pressurised. The pressure is generally between 13 and 15 pounds per square inch (psi). This raises the boiling point of the coolant still further.


The pump circulates the coolant. It pushes the hot coolant from the engine to the radiator where it cools down. From there the coolant returns to the engine. The pump is mechanical. Its power comes from a drive belt connected to the engine.


The thermostat is a valve fitted in the cooling system. The valve monitors the engine’s temperature. If the temperature changes, the valve opens and closes. In this way, it adjusts the flow of liquid through the cooling system.


Coolant arrives at the radiator from the engine. The radiator then lowers the temperature of the coolant and passes it back to the engine. The radiator is a metal box with a series of fins and aluminium pipes. The coolant runs into the pipes, and its heat immediately begins to dissipate. The radiator is usually at the front of a vehicle to benefit from the cooling effect of the air.

Cooling Fan

The cooling fan helps the radiator lower the coolant’s temperature swiftly and consistently. When a vehicle is driving at low speed, or stuck in traffic, there is poor airflow. The cooling fan draws air through the radiator and prevents over-heating. Cooling fans are belt-driven or electric. They sit between the radiator and the engine.


A cooling system needs hoses through which the coolant passes. These hoses connect the radiator to the engine.

Drive Belts

The drive belts turn the cooling fan and provide power to the pump. Their role is simple but essential.


Basic maintenance of a cooling system relies on visual checks. When the engine is cool, confirm that the level of coolant is correct. A vehicle’s coolant reservoir tank usually has two lines across it. The coolant level should lie between these.

Inspect hoses for cuts and coolant seepage. Check belts for wear and tension. A vehicle handbook has full details.

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