Thermostatic Fan Clutch

[1999gmc]

I run the Hayden medium truck one as it has 100%+ more engagement & holding area over the severe duty one w/steel fan. I had more than a few occasions where the severe duty failed when needed in the mountains and desert sw the medium truck unit solved that problem.

Did it engage sooner? Thats my problem, I need it engage sooner. It will run cool if I can get the clutch to engage before a hill its fine and stays cool. But if my clutch isn't engaged and I get to a big hill it will get up over 230 before it engages. I have the Heath severe duty and DMax fan.

 

[WarWagon]

Did it engage sooner? Thats my problem, I need it engage sooner. It will run cool if I can get the clutch to engage before a hill its fine and stays cool. But if my clutch isn't engaged and I get to a big hill it will get up over 230 before it engages. I have the Heath severe duty and DMax fan.

How old is the fan clutch? 5 years is the life limit as they loose ~200 RPM per year.

This is the exact design limit of the spring thermal fan clutch. It has to see enough hot air and overcome it's own lock in delay before the fan comes up to speed. The delay to get the obsolete spring thermal fan clutch locked up is significant in relation to ECT rise. The other solutions posted with on/off fan clutches that use ECT and can come up to full speed now is the next step.

Taking the KD fan clutch I can still sneak up on 210 by heavy throttle, but not WOT, and the engine lugs and heats up before the fan can get on:

From the KD site with a known and documented fan clutch:
Engage temp is 180°f air temp which is 15° lower than the OE spec.

So at heavy throttle the fan sees 180 degree temps and is trying to get on. But the spring has to move and then the silicone has to move all taking it's time while ECT continues to spike from a lack of enough fan RPM. The silicone movement is affected by engine RPM where higher RPM will kick in or out the clutch faster. So if I go WOT and kick down a gear the temp doesn't hit 210 as everything from more water pump flow to fan clutch RPM reduce the peak ECT before the fan comes on and stops the ECT runaway. (This was tested on my 1993 with factory turned up turbo and the recommended steel fan.)

Moving the entire temperature curve down keeps the peak temps at 210 - but the system still spikes. The KD clutch is better than most other offerings as far as getting the fan on the quickest, but, the delay is still an issue.

 

[FellowTraveler]

Did it engage sooner? Thats my problem, I need it engage sooner. It will run cool if I can get the clutch to engage before a hill its fine and stays cool. But if my clutch isn't engaged and I get to a big hill it will get up over 230 before it engages. I have the Heath severe duty and DMax fan.

Only noticeable difference I witnessed is that the severe duty would not stay engaged on hills while pulling a load the heavy duty medium truck unit does stay engaged 'that Heath clutch is the same as the heavy duty medium truck fan clutch from what I have read.'

My 6.5td diesel has a history of hitting 230 deg f on a regular basis on triple digit days w/AC on w/o any noticeable issues before my switch to EVANS.

Air gaps around your radiator entire top of radiator there is a gap under shroud and upper mounts and on both sides down to the lower radiator support "this gap is more likely than not allowing too much air to flow around the radiator core which in turn would not allow enough heat to flow over fan clutch so it engages," I had found this to be a problem on the GMT400 series.

 

[FellowTraveler]

How old is the fan clutch? 5 years is the life limit as they loose ~200 RPM per year.

Everyone needs to keep this fact in mind........