Originally Posted by JohnZo

There are different specs depending on the clutch model. Hayden standard duty thermostatic clutches spin around 70% of water pump speed when hot, only 20 - 30% when cold, for fans with 1 1/2 inch blade pitch. Heavy duty clutches spin faster (up to 90%) when hot and really loud when engaged. But the clutches start out in the hot (engaged) position when first started in the morning. This puts more fan load on the motor and actually helps get up to temp faster (since the t-stat is still closed). Here is a test sequence. Start the truck cold and the fan should be very loud. Then rev up the engine 1500 - 2000 rpm and hold it steady until the fan noise fades away (good clutch function). This can take up to a minute or so while the silicon stuff gets rearranged inside the clutch. It should gradually get quiet and you will hear more engine sound vs fan sound. This test is for thermostatic clutches. Some cheapo clutches only spin one speed. The thermostatic models for Discos have a little bi-metallic coil on the front center.

Originally Posted by Frank4

what would you do to mitigate?