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Radiator fan in cars

Posted On December 3rd, 2019

The radiator fan is used to improve cooling of the coolant by increasing the speed and amount of air passing through the radiator. The fan is usually installed between the radiator and the engine in a special casing.

Structurally, the radiator fan combines four or more blades located on a common pulley. To increase the air supply, the blades are installed at an angle to the plane of rotation.

The radiator fan can have various types of drives: mechanical, hydromechanical, electric.


The mechanical fan drive is a permanent drive from the crankshaft through a belt drive. The disadvantage of this drive is the significant cost of engine power to rotate the fan. Therefore, at present, a mechanical fan drive is almost never used.

The hydromechanical drive of the fan can be represented by a viscous coupling or a hydraulic coupling. The viscous coupling has a permanent drive from the crankshaft. Partial to full coupling locks are performed with increasing temperature of the silicone fluid filling the coupling. An increase in temperature is a consequence of an increase in the crankshaft speed and engine load. Locking the clutch causes the fan to rotate. A hydraulic coupling, in contrast to a viscous coupling, is blocked by changing the amount of oil in the coupling.

The most common is the electric radiator fan drive. The drive includes an electric motor and a control system. The electric motor is powered from the vehicle electrical system. The control system ensures the operation of the fan depending on the temperature of the engine.

On some cars, the function of controlled fan run-out is implemented – automatic switching on of the fan after the engine stops. Fan run-out is made in order to better cool the engine, depending on the mode of operation before stopping.

A typical electric fan control circuit includes a coolant temperature sensor; electronic engine control unit; the fan on the relay and electric motor as an actuator.

The sensor detects the temperature of the coolant in the engine. On modern cars, two sensors can be installed: one at the exit of the engine, the other at the exit of the radiator. In this case, the fan is controlled based on the assessment of the difference in the readings of the sensors.

When operating the fan used other input devices: the rotational speed of the crankshaft sensor, airflow meter. Their readings are taken into account when determining the engine operating mode.

Signals from the sensors are transmitted to the electronic engine control unit, which processes them and, if necessary, activates the fan enable relay. The fan starts to run.

On cars equipped with an air conditioner or towing device, as a rule, two fans are installed, each of which serves its own relay on. Depending on the temperature, the fans can operate both separately and together.

Recently, instead of a fan enable relay, a fan control unit has been used, which provides efficient and economical operation of the fan.

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