What You Need to Know About Your Car Radiator Fan

What You Need to Know About Your Car Radiator Fan

A radiator fan is important to keep your engine cool and avoid overheating. There are two types; mechanical and electric. Mechanical fans are clutch-based and attached to the water pump pulley. They can have either straight or flex blades that flatten at higher RPM and engine speed.

A push type fan inhibits the free flow of air to the radiator at idling and low speeds. If you have a dual fan setup a pull type fan is best.


The radiator fan motor takes the heat from the coolant and blows it away to help keep the engine running within its optimum operating temperature range. This is essential for power, efficiency and emissions. When the fan motor fails, air is unable to move through the radiator and the engine overheats. It is possible to drive a short distance if the cooling fan doesn’t work properly, but overheating will cause serious damage to the engine and potentially other parts of the vehicle.

The first thing to do is check that the fuse for the radiator fan has not blown. This car radiator fan could be caused by a faulty fan motor or other problems with the cooling system. If the fuse is OK, then check that the thermoswitch is functioning. You can do this by leaving the ignition switched on and putting a circuit tester across the feed wire to the thermoswitch (do not disconnect the leads). If there is current passing through the switch, it is working.

Next, you can check that the motor is working by putting a test light or circuit tester on its live lead to the relay (with the ignition still on). If there is no current at all, the fan motor is faulty. This is the easiest part of the fan to replace, so it is a good place to start.


The clutch is the part that keeps your car radiator fan engaged and turning at the proper speed to cool the engine. It’s usually made of a tough material like friction-lock or abrasion-resistant polycarbonate. But, just like all other parts of your vehicle, it will eventually wear out. When it does, your cooling fan will stop turning. That’s why it is important to inspect the radiator fan clutch regularly.

You can check for a bad or worn-out fan clutch by looking for several signs and symptoms, including a lack of power when you accelerate or lower engine RPM, overheating, and/or reduced fuel efficiency. You may also notice that your fan is not turning even after the engine has cooled down.

There are two main types of clutches for the radiator fan. The first is the thermal type, commonly found in rear-wheel drive vehicles. The bi-metal thermal spring mounted on the front of the clutch expands or contracts based on underhood temperatures. When the temperature is high, the fan clutch opens a valve that releases silicone fluid into a chamber within the clutch. The liquid then engages the fan to turn it at 70 to 90 percent of the water pump’s speed.

The second type of clutch is the non-thermal type that combines a viscous or fluid coupling with a bi-metal sensor to control engagement. The sensors can be controlled by the ECU and are influenced by inputs such as engine/transmission oil temperature, engine coolant temperature, AC system pressures or ambient air temperature.

Temperature Sensor

Your car’s radiator fan helps cool the engine by moving air over the cooling fins. It’s usually rated in CFM, or cubic feet of air per minute, to indicate how much it moves. For a powerful engine, you’ll need a larger fan that can move enough air to keep the engine from overheating, which can cause expensive damage or even destroy the engine.

A radiator fan is part of the vehicle’s cooling system, along with the radiator, water pump, thermostat, and hoses. When it’s working properly, you’ll hear a whirring noise when the fan is spinning. If the fan stops running, you should check to see if the engine is overheating, which can lead to expensive and potentially dangerous repairs.

The fans in modern cars are controlled by the engine coolant temperature sensor, or a separate fan control module. If the coolant temperature sensor is broken, or if it’s not reading correctly, the fan won’t turn on. A multimeter can be used to test the wiring from the fan to the control module and relay, checking the connector plugs for signs of corrosion. If the wires are good and the fan still doesn’t activate, there could be a problem with the relay or control module. In this case, you’ll need to replace it. You can also try bridging the radiator fan relay to see if it will activate the motor.


Many of the more energy-intensive underhood components of modern vehicles operate with the help of relays. The radiator fan is no exception. Relays are electromagnets that switch on and off by using a small current to close a circuit. This allows the relay to control larger currents without overloading the switch/device it controls.

When the engine running temperature of a vehicle approaches dangerous levels, the computer or car radiator fan temperature switch activates the fan relay. This completes an electrical circuit and lets the relay’s electromagnet anchor attract an electric current that energizes the cooling fans.

The cooling fans (one or two on some cars) pull air through the radiator and coolant system to reduce the engine’s operating temperature. The fans can also pull air through the air conditioner and pass it through the condenser to decrease the pressure of the refrigerant.

When the radiator fan relay fails, the coolant fan motor cannot get the power it needs to run properly. One of the most common symptoms is an engine that overheats while driving or when parked and running at a stop. Another symptom is when the fans themselves do not come on. If the fans are not working, a multimeter can be used to verify that they are receiving power from the relay terminals. If not, a relay from a noncritical system that operates the same way can be swapped out for testing purposes.

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