Gold Founding Member
Join Date: Aug 1998
Location: the Seasonally Frozen Wastelands
They can fail in many ways.
1. Any fluid leakage means it's toast.
2. They can seize solid. That's the "sounds like an airplane" way.
3. They can fail to engage. Engine overheats.
4. With the clutch firmly bolted to the waterpump, any fore/aft play in the fan blades means the bearings are shot. This often happens before the bearings lock up, as in #2 above. If the thing craps out the bearings badly enough, the fan goes through the radiator. Ouch.