Yesterday I discovered the fan clutch on my '92 M998 was stuck in the locked position. I disconnected the fan hose from the Cadillac valve, applied 120 psi of air pressure to it, and the fan didn't release. I was able to free it up with the following procedure. This was all done with the engine firmly off, and my kids where they couldn't possibly try to turn the truck on and remove my arm.
Your mileage may vary, but I hope this helps anyone who may have a stuck fan clutch. The engine no longer sounds so much like it's a giant window air conditioner under the hood
- Disconnect fan hose from the Cadillac valve, and apply and hold air pressure (120 psi in my case). The Cadillac valve is under the hood, bolted over the driver's side wheel.
- Climb up onto the passenger side wheel, and with a small mallet, reach between the fan blades, and tap, pretty gently on the fan mount plate (not the fan clutch nose).
- Rotate the fan a bit, reached through, and tap again.
- I repeated this rotate-tap sequence about 3 times before the clutch started to release, and maybe a total of 5 times before the clutch was completely free. It didn't take much force.
Your mileage may vary, but I hope this helps anyone who may have a stuck fan clutch. The engine no longer sounds so much like it's a giant window air conditioner under the hood