Posted this over on cumminsfoum but didnt get a response:

What is the spec on the air temperature the factory fan clutch locks up at? I know the thermostat starts to open at 181* and is fully open at 203*.

I did some googling and couldn't find anything about the fan though. I was testing my fan clutch today by holding the truck in park at 2k RPM. With the AC off the temp climbs to about 210* and then the fan starts roaring and temps drop down to about 190 after a minute or so and start to slowly climb again till 210* when the fan again kicks in. Does that sound about right? It bothers me a little that it runs on the high side of 190* in traffic unloaded, but once it gets a little hot the fan does roar to life.

If I do replace it whats the best bang for the buck? I was looking at the hayden clutches.

 

Sounds like its working right .. it works on radient temps .. not on actually engine temp, so you may be seeing those swings is due to the fact that the temp sending unit is in the drivers side rear most part of the cyllinder head ..

Might try installing a seperate temp sensor closer to the t-stat .. might notice much closer temps and not such a dramitic swings ..

 

Well ended up slapping a hayden clutch on there since I head they engage a little sooner and am happy with it. Truck runs about 10* cooler overall and at idle it wont come off the 180* area even reved up to 2k. Fan might run a little excessively as it seems to be on more often than not, but I have only driven it a few miles and it was in traffic and about 90* out so it could have just been warm enough out. Also noticed it looked like the clutch I took off might have had a slight fluid leak out where the bi-metallic spring is.

 

Had issues with the AC being hot at idle with the Hayden clutch….switched to a mopar clutch and it works great and kicks in at 190* as well.

 

yeah sometimes the aftermarket ones just dont work as well as they would like to think they do .. have this happen all the time with big Engines ..