On engines with belt-driven cooling fans, a fan clutch is usually employed to sve vitality and reduce noise. The fan clutch disengages slows or disengages the engine’s cooling fan when more cooling isn’t required. The fan pulls air with the radiator and air conditioning condenser if the motor vehicle isn’t moving quickly sufficient to supply adequate airflow for cooling. A fan can consume up anyplace from a number of horsepower as much as 12 or 15 hp on a significant V8, so by lowering the parasitic horsepower reduction on the engine the fan clutch makes a noticeable difference in fuel economy.

The fan clutch also minimizes noise by slowing down or disengaging the fan at high way speeds, and a few even assistance speed engine warm up all through cold weather.


thermal kind cooling fan clutch There are two simple types of fan clutches: thermal and non-thermal (also termed “torque limiting”). Thermal fan clutches have a temperature-sensitive bimetal coil spring about the front that reacts to temperature alterations. Once the air coming through the radiator is hot, the spring expands and opens an inner valve that decreases clutch slippage. This causes the fan to spin quicker for improved cooling. As the air cools, the spring contracts and closes the valve. This increases the quantity of clutch slippage, allowing the fan to slow down and reduce cooling.


cooling fan clutch cutaway The clutch includes a fluid coupling full of a silicone based mostly oil. Inside the cutaway view at the left, the region involving the teeth around the clutch plates is filled with silicone fluid. An inner valve opens and closes a passage between the primary fluid cavity and also a fluid reservoir. If the passage is open, fluid enters the clutch and makes the fan to turn speedier. When the valve is shut, fluid flows back towards the reservoir but doesn’t return, triggering the clutch to slip and also the fan to turn more gradually.

The non-thermal (torque limiting) fan clutch does not possess a temperature sensing capability. It reacts only to speed, slipping to restrict utmost fan speed to about 1200 to 2200 rpm relying on the application.


A slipping fan clutch is commonly overlooked as the lead to of an engine overheating issue.

As being a fan clutch ages, fluid deterioration progressively leads to a rise in slippage (about 200 rpm per year). Just after numerous many years of service, the clutch may possibly slip so badly the fan cannot hold up together with the cooling demands on the engine plus the engine overheats. At this time, replacement is often required.

Other indicators of fan cluch failure would contain any looseness from the clutch (verify for fan wobble), or oil streaks radiating outward in the clutch hub.

In the event the clutch is binding, the fan might not release causing excessive cooling and noise, in particular at highway speeds


A good clutch ought to offer a specific volume of resistance when spun by hand (engine off, obviously!). But when the fan spins with tiny resistance (over 1 to 1-1/2 turns), the fan clutch is slipping excessive and needs to be replaced.

If the fan binds, doesn’t turn or offers a lot of resistance, it has seized and also needs to be replaced.

Fan speed also can be checked by having an optical tachometer, by marking one of the fan blades with chalk and utilizing a timing light to observe speed improvements, and/or listening for modifications in fan noise as engine speed adjustments.

You should also seek to wiggle the fan blades by hand. If there is any wobble within the fan, there exists a bad bearing in the fan clutch, or maybe a worn bearing around the water pump shaft. A undesirable water pump bearing will normally result in the water pump to leak and/or make noise, but not normally. Remove the fan clutch and see if the play is in the water pump shaft. If it feels tight (no play or wobble), change the fan clutch.
fan clutch cutaway
What’s inside a mechanical fan clutch


Quite a few experts say it’s a great concept to replace the fan clutch on the very same time since the water pump in case the water pump has failed. The main reason is simply because the two age at concerning the very same rate, so in the event the water pump has failed, the fan clutch might also fail quickly. As as we described earlier, a large mileage fan clutch may be slipping excessively expanding the chance of overheating.

Once you invest in a replacement fan clutch, make certain you get exactly the same sort (thermal or nonthermal) as the authentic. It is possible to normally upgrade from a nonthermal to a additional productive thermal fan clutch, but by no means the reverse. Or, you may get rid of the fan and clutch altogether and set up an aftermarket electric fan kit to cool the radiator.