How the Cooling System Works?

How the Cooling System Works?

Combustion engines generate a lot of heat, and to prevent the metal components from overheating, fuel-burning cars need a way to transfer the heat from the engine to the outside air. This is the job of the cooling system.

Most cars have a liquid cooling system, which uses a liquid coolant that runs through the engine and is then pumped into a radiator to transfer the heat to the air. Car engines run at nearly the same temperature that water boils (212°F or 100°C), so they must use a combination of coolant and water to allow the coolant to run hotter than straight water. In cold temperatures, the same liquid acts as an antifreeze, preventing the water from freezing and expanding, which can crack metal parts.

Here are the common components of a liquid cooling system.


The radiator is usually mounted on the front of the car. Coolant from the engine is pumped through it and the heat
from the coolant is transferred from the tubes to the small fins lining the tubes.

As air flows over the fins, the heat is transferred to the surrounding air. The engine then pumps the cooled coolant from the bottom of the radiator back into the engine to pick up more heat.

Water Pump

The water pump takes cooled liquid from the bottom of the radiator and pushes it through the engine and then
back to the radiator. The water pump may be driven by a belt from the engine, or electrically from the alternator.


The thermostat regulates the engine temperature. Since metal expands when it heats, the engine is designed to run best at a heated temperature. If the engine takes too long to come up to temperature it can cause problems. The thermostat senses when the temperature has reached an optimum point and then opens up, allowing the coolant to run through the radiator.

Cooling Fan

A cooling fan is used when the car is not moving fast enough to allow air to flow over the radiator. Cooling fans are mostly electric, but they can be powered by an engine belt. Mechanical fans sometimes use a clutch to allow them to spin freely when the car is moving fast enough, saving energy. Electric fans can be turned on and off by temperature sensors or by the computer.

Heater Core

The waste heat from the engine is used to heat the inside of the car when needed. It does this using a heater core. The heater core looks like a miniature radiator, and it works just like the radiator by transferring heat to the surrounding air. It is usually mounted in a box under the dash alongside with the air conditioner evaporator.


Most engines use a combination of hoses and tubes to transfer the heat from the engine to the radiator and the heater core. The flexible hoses allow the engine to move during operation and are usually held in place with clamps.

Overflow Tank

An overflow tank, also called a de-gas tank or coolant reservoir, is used as a reservoir for extra coolant. As the engine heats up and cools down, this tank holds the extra coolant, ready to be delivered by the water pump. It also provides a safe way to check the coolant level and add more coolant, if needed.


The coolant, or antifreeze, is the liquid component of the liquid cooling system. It takes heat out of the engine and prevents the cooling system from freezing in low temperatures. Antifreeze is designed to be mixed with water, so don’t run straight antifreeze in your car. It is also highly toxic, but has a “sweet” smell that makes it attractive to dogs and other animals. Keep it away from pets and children.

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