Because internal combustion engines create heat of extremely high temperature, the cooling system is employed. The circulation of the cooling will determine how long the engine and its component will serve. In automobile engines, the cooling process is either by water or air, but both processes have their effectiveness. Although lubricating oil also helps in cooling the parts of the engine to some extent.


Much has changed over the years on automobiles, but there is no much change in the engine cooling system. Well, modern designs are more reliable and efficient doing the circulation through the engine. The design is so efficient that, it maintains the engine at a constant temperature. Even if the temperature outside is hot to about 110 degrees Fahrenheit or 10 below 0, the cooling still remains constant. Fuel economy might suffer and emissions will rise.

Today we’ll be looking at the definition, functions, components, diagram, types, working principle as well as maintenance and repair of a cooling system in internal combustion engines

What is the Engine Cooling System?

The cooling system is a set of components that enables the flow of liquid coolant to the passages in the engine block and head so as to absorb combustion heat. The heated fluid will then return to the radiator through a rubber hose, for cooling. As the heated fluid (hot water) flows into the radiator through the thin tubes, it gets cooled by an air stream.

Modern internal combustion engines cooled with both water and air, but some engine uses either air or liquid to remove the waste heat from the engine. Special purpose or small engines are cooled using air from the atmosphere, which makes the system lightweight and relatively less complex. While in some engines, heat is transferred from a closed loop of water to the radiator where the cooling is achieved.


Water has a higher ability and can quickly move heat from the engine than air. The components in the water cooling system add weight, complexity, and cost to the engine. The system is good for higher-power engines that produce more waste heat but can move more weight.


Functions of Engine Cooling System

Below are the functions of a cooling system in internal combustion engines:


The essence of the cooling system in IC engines is because the temperature of the burning gases (combustion gas) in the engine cylinder is up to 1500 to 2000 degree centigrade. This is above the melting point of the material of the cylinder head and body of the engine. therefore, if the heat is not dissipated, serious problem and failure occur to the cylinder material.


Another function of the cooling system in the automobile engine is to reduce the temperature of lubricating oil that lubricates and cools the moving parts. Very high temperature causes the film to the lubricating oil to get oxidized, which produce carbon deposit on the surface. This often results in piston seizure.

Because too much heat removal lowers the thermal efficiency of the engine. The system is designed to remove at least 30% of the heat generated the combustion chamber.


A functional cooling system should be able to remove heat at a fast rate when the engine is hot. Engines are cool during the starting, much cooling is not needed so that the working parts can reach their working temperature in a short time.


Higher temperatures lower the volumetric efficiency of the engine. And because of overheating, larger temperature differences will result in distortion of the engine components due to the thermal stresses set up. For this, a functional cooling system is required to keep the temperature variation normal.

Components of Engine Cooling System

Below are the components of the cooling system in an internal combustion engine and their functions:



This engine cooling part is made up of aluminium tubes and strips that zigzag between the tubes. High-temperature fluid flows inside the radiator through a hose. This heated fluid is then transferred from the tube to the air stream, which is then blown away to the atmosphere.


Cooling Fan:

The cooling fan is located a bit after the radiator, which is closest to the engine. the part is designed to protect fingers and direct airflow. It blows air to the radiator to cool the hot fluid while the engine is running, so the fan helps to cool down the temperature of the radiator.


A modern electric fan is controlled by the vehicle’s computer. There is a temperature sensor that monitors the engine temperature and sends the information to the ECU.


Pressure Cap and Reserve Tank:

Radiators are now designed with pressure cap so that pressurize coolant flow out as it expands. Thus, the function of the pressurize cap is to maintain pressure in the cooling system up to a certain point. This cap featured a spring valve, calibrated to the correct pounds per square inch (psi). if the pressure is up higher than the set pressure points it opens and asmall amount of coolant is bleed off.


Reserve tank is a reservoir that collects the coolant bled off from the pressurized cap. The tank is typically made with plastic, and it can indicate the temperature of the coolant.

Water Pump:

Water pump another important component of an engine cooling system. It’s mounted on the front of the engine and It keeps circulating the coolant as far the engine is working. The part is made of cast iron or cast aluminium and an impeller blade that pump the coolant.



A thermostat is simply a valve that sense or measures the temperature of the engine coolant. If the coolant is not hot enough,

the thermostat remains close, but as soon as the coolant temperature reaches some specific temperature, it opens and allows the coolant to flow through the radiator.

Heater Core:

Hot coolant a lot serve better purposes to the car interior when required. To achieve this, the cooling system is designed with a heater core that many lookalikes with the radiator. The component is connected using a pair of rubber hoses to collect and return the coolant from the water pump to the top of the engine. There is a fan blower that blows the heater core which then supplies heat from the hot coolant to the car interior.


The complete circulation of coolant from the radiator to an internal part of the engine back to the radiator and some associate components is achieved by hoses. But the main hoses are known as the upper and lower radiator hoses. They are bigger and wider compared with others.

Bypass System:

This component work when the coolant in the engine is hot enough to open the thermostat. Thus, it allows the coolant to bypass the radiator and return directly to the engine so the coolant temperature can be balanced. it’s often available are rubber hose, but some manufacturer uses a fixed steel tube.

Cylinder Head Gaskets and Intake Manifold Gaskets:

This component also helps the engine cooling system as it securely tight the mating surfaces of the combustion chamber. It prevents coolant and oil leakage out of the engine or into the combustion chamber. Even as the mating surfaces are precisely machined and tight, coolant can still flow through it. This is why the gaskets are employed.


Freeze Plugs:

This is a part in the engine that manufactured with special sand along with molten metal. It moulded to the shape of the coolant passages in the engine block. Coolant flows through the part which is why it must plug to the hole else the coolant will pour right out.


Most of the cooling system components have been fully discussed in a fresh post. You should check them to have a clear understanding of them.

Working Principle

Just as earlier mentioned, the automotive cooling system is of two types. In this explanation, we’ll be covering the working of water cooling system. The system is made of passages inside the engine block and heads and a water pump that circulate the coolant. It is also made of a thermostat that controls the temperature of the coolant and a radiator cap to control the pressure of the system. The coolant flow to all these spots with the aid of interconnected hoses.


Water cooling system work by transferring liquid coolant through passages in the engine block and heads. The coolant flows from the radiator to absorb excessive heat production during the combustion process. After the coolant receives the hotness, it’s transferred to the radiator through a rubber hose. As soon as the hot coolant enters the radiator, cooling begins. The cooling is achieved by the air stream entering the engine compartment from the front side of the vehicle.


After the coolant is cooled, it returns to the engine to carry out the same process. The water pump helps the circulation of coolant to enter toward the hidden passages. There is the thermostat located between the engine and the radiator to ensure the coolant is heated to a certain preset temperature before entering the radiator. The thermostat remains close, if it senses cooled coolant, so instead of stopping the circulation process it then bypasses the radiator and returns to the engine.


The cooling system is designed with a pressurizing valve to prevent the coolant from boiling. Since under pressure, the boiling of the coolant will raise, the radiator cap is designed to relieve pressure if in case it exceeds a certain point. Or else, too much pressure will destroy the system components like hoses and other parts.