Cooling Fan Operation


Cooling Fan Operation

When your vehicle is running the oncoming air is forced through the radiator cooling the mixture of water and antifreeze (engine coolant) that circulates inside the cooling system. But once you stop the car there will be no airflow, so the excessive heat absorbed by the coolant from the engine will not release efficiently. This is when a radiator fan comes into play. It forces air through the radiator, removing the heat from the coolant.


Depending on your vehicle’s make, model and year of production, it can be equipped with either a mechanical or electric cooling fan.

Electric cooling fan

All modern vehicles come with one or, rarely, several electric cooling fans. A typical electric cooling fan consists of an electrical motor that moves fan blades causing them to draw air through the radiator. The fan motor is engaged when the engine (coolant) temperature exceeds a set parameter and continues running until the engine cools down to its normal operating temperature. An electric cooling fan should also stop operating once you shut down the engine.

The engine temperature is constantly monitored while it’s running. This is a job of an engine temperature sensor which can also serve as an electrical switch that controls the fan motor. In other cases the function of the electrical switch is performed by a fan control relay or the engine control module. Besides, a lot of modern vehicles come equipped with a fan running at different speeds based on the engine temperature.

Signs of a failing electric cooling fan

The main symptom of a bad cooling fan you should pay attention to is engine overheating, especially if you’re driving at a low speed. In addition, your A/C may not operate properly.

Mechanical cooling fan

If you drive an older vehicle produced before the new millennium, most likely it has a mechanical cooling fan. In this case fan blades are mounted on a pulley driven by a belt. It also works in conjunction with another cooling system device known as a fan clutch. The latter contains a hub with silicon gel which expands at high temperatures and engages the fan blades, causing it to force air through the radiator. Once the silicon cools down the fan is deactivated since the clutch no longer locks the fan. Such smart management allows for preventing unneeded loss of engine power. 

Signs of a failing mechanical cooling fan

The most common problem is a failed fan hub coupling. This may lock the fan resulting in a rising noise, which sometimes is identified as “roaring” when accelerating and increased fuel consumption. If the silicon leaks out, the fan blades will never be engaged, which will cause engine overheating at lower speeds.

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