To answer your question about fan clutches JE13BigHorn; Many different type of clutches to fans depending on the vehicle requirements; A Standard, Heavy Duty, and a Severe Duty. But as far as typical operation, fan clutches are either Thermal or Non-Thermal(also known as Centrifigal). Our Ram uses the Thermal, which when starting cold, the fluid inside the clutch has settled in the working area from sitting overnight. This is what engages the clutch fan at first startup but disengages shortly after. The air temp coming through the radiator is sensed by the thermal spring on the front of the thermal fan clutch. It expands and contracts with the change in air temp operating a valve inside the clutch. When cold, the silicone drive fluid is pumped from the working area to the reservoir. When hot, the valve opens allowing fluid from the reservoir to be transferred to the working area thereby increasing the fan speed. The clutch disengages as the air temp decreases, closing the valve and allowing the silicone fluid to be pumped back into the reservoir. SOOOO, long story short, a thermal fan clutch is engaged on a cold start up because the fluid has drained into the working area when the engine is shut off. The fan clutch will slow down shortly after startup as a result of a pumping action produced by a difference in speed between the shaft and the body of the clutch.