greenteagod
+1y
Found this from a member on a hotrod site. In doing some simple google searches I've found other people performing similar tests to check if the fan clutch is bad:
"Start with the car off. Jiggle the fan forward and back. If there is any play at the clutch shaft, its bad. Give the fan a spin. It should move freely, but stop almost instantly, as if the clutch were filled with mashed potatoes. Start the engine. The fan should turn pretty briskly; almost as fast as the crank. Now use a rolled up newspaper to gently try and stop the fan. You should be able to when its cool. Throw away the ruined newspaper. Rev the engine, you should notice that the fan increases speed, but not proportionally to the crank speed. The clutch is full of viscous fluid, so the air friction on the fan starts overcoming the friction of the fluid in the clutch and it stops accelerating with the engine. The fan won't roar. Then let it get hot. You might have to drive it around some stop and go streets to get it to lock up the clutch. Now when you accelerate, you should hear the fan roaring a little louder. If you stop the car, shut off the engine, and try to spin the fan, it shouldn't move."