Cooling System - Fan Clutch
When engaged, the fan drive activates the fan to cool the engine by pulling air through the radiator. Depending on the size and rational speed of the fan blade, as much as 70-75 HP may be needed to run the fan. This saves power since the engine does not have to fully drive the fan.
Causes of fan clutch failure: A common symptom of fan clutch failure is overheating at idle or in heavy traffic. You may also experience a failed fan clutch when it is stuck in the on position drawing engine power when there is no need to (which results in decreased fuel economy).