RedValor: I replaced mine with ACDelco 15-4684 but it doesn't look like this part is available any longer. This was supposed to be the OEM part I think, and it looked pretty much the same.

George: Thanks for posting the service manual. I learned two things. First, the fan clutch is supposed to have more resistance when hot. Second, the fan clutch is supposed to engage between 185 and 205 F. And then of course disengage as the engine cools down.

This is a far better way to test the fan clutch than just turning it and feeling for binding or free-wheeling or excessive resistance.

 

Your welcome, knowledge is power.


George

 

I'd hate to keep bringing up questions, but I noticed another development with this second Duralast clutch.

What I observe:
The clutch does engage as stated in George's manual after 185 degrees F, and then disengages once cooled or RPM exceeds a high threshold. This seems to be correct behavior. What I'm not so sure about is the clutch continuing to be engaged well after the truck has achieved a suitable cruising speed (i. e. 45+ mph). I certainly expect the clutch to stay engaged while at 55 mph under severe conditions, but not when the coolant temp is under 210 degrees, cruising at 55 mph, while the outside temperature is 78 degrees during a mild Florida rain storm. There are times I notice that the clutch would also engage without the AC being turn on at all in low 80s degree weather at night (so there's no heat off the condenser).

I may be sounding paranoid, but the fact that the clutch stays engaged at highway cruising speed brings forth mpg concerns. Just want make sure this sounds like normal operation before I pull the trigger on trying a different brand. Is this intended OEM cooling design? Is the clutch suppose to stay engaged at highway cruising speed while coolant temp hovers around 193 degrees?