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Repair Topics > Cooling System Service > Radiator fan not working

Radiator fan not working

What causes radiator fan not working condition?

There are five causes of a radiator fan not working condition

Blown fuse — electric radiator fans

Check the fuse(s) for the electric radiator fans. If one or more windshield wiper fusefuses are blown and the replacement fuse blows as well, check for fan blades for debris and ease of rotation. An electric radiator fan should spin freely. If it doesn’t, chances are the bearings are worn and the fan must be replaced.

Faulty radiator fan relay(s)

Carmakers use many different relay configurations to achieve multiple radiator fan speeds. To make radiator fans run at a low and high speed, some carmakers use a series-wired set of three relays. Other carmakers use two relays, while some carmakers use a solid-state radiator fan relay the pulses power to achieve infinitely variable radiator fan speeds.

Check a shop manual to see what type of speed control system is used in your vehicle. Don’t assume that because the fan is running, it’s running at the correct speed for the engine temperature.

car overheats, radiator fan fuses, fan relay

GM 3-speed radiator fan wiring diagram

Faulty coolant temperature sensor or a problem with the coolant sensor wiring

The powertrain computer determines when to activate the

where is the engine coolant temperature sensor

Engine coolant temperature sensor is usually located near the thermostat housing

radiator fans based on temperature readings from the engine coolant temperature sensor (CTS). The CTS is usually located near the thermostat housing. However, in some engines, it’s located in the cylinder head or radiator.

CTS sensors provide a variable resistance based on coolant temperature. Locate the resistance/temperature chart in a shop manual. Measure engine temperature and compare to the resistance reading from the CTS. Replace the CTS if the reading doesn’t match the shop manual.

Faulty clutch on belt-driven radiator fan

Carmakers often use a viscous clutch on a belt-driven fan. The clutch engages at low speeds to drive the fan along with engine RPMs. However, at higher speeds, where air coming through the radiator can cause a drag on the engine, the viscous clutch allows the fan to free-wheel, thus saving engine power.

The viscous clutch mechanism is filled with a silicone fluid that can be thermostatically controlled or electrically controlled. If the fluid leaks out, the thermostat fails or the electrical flow control device fails, the fan will free-wheel at low speeds, causing an overheat condition. The overheat may disappear when the vehicle is driven at highway speeds. This is because the “ram-air” effect of high speed causes enough air to pass through the radiator to cool the engine.

radiator fan clutch

Three types of belt-driven radiator fan clutches

If you have a belt-driven fan and your engine overheats at idle but not at highway speeds, AND your coolant level is at the proper level, you may have a faulty radiator fan clutch.

©, 2020 Rick Muscoplat

Posted on by Rick Muscoplat

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