I think that I need a new fan clutch on my K20. It never runs hot unless I am running in the mud, which is close to full throttle. Otherwise, both idleing(sp) and normal driving are fine. With the engine off I can spin the fan and it will go around several times before stopping, hardly any resistance. There are two different fan clutches offered for my truck, thermal and non-thermal. Which would be best for me? I do mostly street driving, occasionally pull a trailer and play in the mud.