Originally Posted by xntrik
fan clutch drives when the air temperature through the radiator exceeds the thermostat setting of the clutch.
220* coolant temp is too high.
A fan clutch will totally lock up when engaged
It disengages by temperature and high rpm.
I also don't like HD rated clutches, as they don't disengage by rpm until a higher range, and become audible in the vehicle at 40-50 mph when you shouldn't need a fan anyway above 30.
I made a mistake once and installed a HD one on my "TownCar" (high gear w/OD) and at 100+ ambient it hummed until 78 mph.
Took it back and got a standard duty.
I agree completely. I have an HD on my 454 and it locks up at all the wrong times. Its much more viscous so it spins exceptionally strong when its coldest... exactly when you DON'T need it. The coolant has actually never made it to a temp where the fan has locked up.
I also think that its quite possible that your idling experiment isn't a very accurate test. Getting that airflow moving is the key. At idle there might not be enough air moving over the clutch to heat it up. The coolant might be 220, but its possible that the clutch only sees 190. I might let it idle until its really hot, then drive it.
But, its kinda a moot point... I suggest getting a standard clutch.