* Worn or damaged clutch hub: The fan clutch itself is a viscous coupling. Over time, the fluid inside can degrade or leak, reducing its clamping force on the pulley. A severely degraded clutch might allow the pulley to slip or even become loose. This is the most common cause.
* Loose pulley bolt: The nut or bolt securing the fan clutch pulley to the water pump shaft can loosen due to vibration. This is less common if the bolt is properly torqued, but it's a possibility.
* Damaged water pump shaft: In rare cases, the water pump shaft itself might be damaged or worn, preventing the clutch from gripping properly. This often leads to other problems like water pump leaks.
* Incorrect installation: If the fan clutch was recently replaced, it might have been installed incorrectly, leading to a loose pulley.
What it's connected to on the engine side:
The fan clutch pulley is directly mounted onto the water pump shaft of the 4.2L engine. The water pump is driven by the engine's timing belt or chain (depending on the specific engine configuration), which means the pulley spins at engine speed. The fan clutch itself engages and disengages the fan depending on engine temperature.
