Signs that a fan clutch is going bad include vibration, excessive fan noise at any speed, bad air conditioner performance at idle or low speed and failure to increase speed when the engine gets hot. Other symptoms, such as free-wheeling, looseness and leaking fluid, also indicate a worn fan clutch can be ascertained by examining the fan manually.
Fan clutches are located between the water pump shaft and the engine fan. They provide a more efficient cooling system for the engine by regulating when the fan turns on and off or can operate at lower speeds, such as when the vehicle is traveling at a high rate of speed.
There are two varieties of fan clutch: thermal and non-thermal. Non-thermal clutches operate based on the speed of the water pump shaft. Thermal fan clutches operate based on temperature changes in the engine bay, making them somewhat more sophisticated than non-thermal fans. These fans use a bi-metal thermostatic coil to determine when they engage to cool the engine.
Both types of fan clutch share the water pump shaft and the operation of each affects the operation of the other. Worn bearings on the clutch cause the water pump bearings to wear, and the reverse is also true.