Fan Clutch Operation & Troubleshooting
The Fan Clutch is a component of the cooling system that varies the fan speed to meet the cooling needs of the engine. Nearly all rear wheel drive vehicles use Fan Clutches to control fan speed because of their ability to provide high volumes of air and good fuel economy. Despite their popularity, they are one of the least understood cooling components. There are two types of Fan Clutches, the Non-Thermal (also called centrifugal clutches) and the Thermal Fan Clutch.
Non-Thermal Fan Clutch
Thermal Fan Clutch
The air temperature coming through the radiator is sensed by the bi-metal thermal spring on the front of the thermal fan clutch. It expands and contracts with the change in air temperature operating a valve inside of the clutch. When cold, the silicone drive fluid is pumped from the working area to the reservoir. When hot, the valve opens allowing fluid from the reservoir to be transferred to the working area thereby increasing the fan speed. The clutch disengages as the air temperature decreases, closing the valve and allowing the silicone fluid to be pumped back into the reservoir.
A thermal fan clutch is engaged on a cold startup because the fluid drains into the working area when the engine is shut off. The fan clutch will slow down shortly after startup as a result of a pumping action produced by a difference in speed between the shaft and the body of the clutch.
Most models are designed to duplicate original equipment performance. Some Chevrolet/GMC truck models are specifically designed to engage at lower temperatures than the original equipment parts that they replace.
Thermal Fan Clutch Design Types
Hayden makes three different types of thermal fan clutches; Standard, Heavy and Severe Duty. Each type is engineered to simulate the performance, fit and appearance of the original equipment clutch that it replaces. All fan clutches are for specific applications and should only be applied for which they are cataloged. Use of the wrong fan clutch may result in poor cooling, excess noise, reduced mileage, or fan clutch failure.
Standard Duty Thermal
Severe Duty Thermal
Hayden now has available Truck Fan Drives for Ford and General Motors medium-duty trucks and buses.