Check fan clutch?

[88 K30]

I added a tranny cooler recently and my truck started running hotter when towing than it did prior to adding the cooler. I checked for debris and found nothing to speak of. I was thinking maybe my fan clutch is not quite up to par, since based on what I have read here, the fan should really howl when it engages, and I'm not sure I've ever really noticed it. Of course, I currently have an exhaust leak, so it's hard to tell, but I decided to check it yesterday with a heat gun.

The question is: How much resistance should there be when turning the fan by hand after heating it with a heat gun? Should it almost totally lock up? Mine might have gotten slightly tighter than when cold, but it didn't seem as tight as I thought it should be for the amount of heat I applied.

Also, what is the typical life expectancy of the clutch? My truck is almost 20 years old, but only has 76K on it. Should the clutch be worn out?

Thanks!

[88 K30]

OK, so I searched the forums and found a similar topic where it was stated that some resistance should be felt if you heat the coil on the clutch. Shouln't it be a pretty noticeable amount over a cold engine, even if it doesn't lock up totally? I guess I can test it on another old fan clutch I have laying in the garage to see how it behaves (if it is any good...).

[More Power]

The fan-clutch should engage while in-town driving, such as stoplight to stoplight on a hot day, especially with the A/C on. You should hear the roar of the fan while accelerating away from a stop.

While driving at highway speed on a hot day, you should hear the fan whenever the engine temp crosses 210. Having A/C on should allow this to happen sooner and more often.

There is no mistaking the sound of the fan with an engaged fan-clutch. If you're not sure whether it's engaging, it probably isn't.

According to GM, the 6.2L fan-clutch should engage when the air temperature at the thermostatic coil crosses 165 degrees F.

I'd bet most 20 year old fan-clutches are way past due for replacement. And, a bad fan-clutch is the one of the leading causes for 6.2/6.5 overheating problems. Hearing the fan roar is a good thing!

Jim

[88 K30]

Jim, Thanks for the reply. Wow!! 165 degrees seems pretty low. I guess that is the starting point and it locks up tighter as the temp increases? That means it should be engaged with my truck just idling at operating temperature? It is hard to say with nothing to compare it to, but it does pull a good amount of air when it is idling and I rev it up with the hood open, but maybe it's not enough. My truck runs down the road at 45mph with no load at 205 (according to the stock gauge) with a 195 t-stat. It has always worked up to 215 or 220 on a long, hard grade with a 6000lb trailer (and no A/C - it's getting fixed soon though!), but I have never had it go any higher until I added the tranny cooler. I guess I will order up a new one and see if it helps. I also have a Robertshaw 180 t-stat to install, but I was waiting until I could install my Banks Sidewinder kit. If they ever get my new garage finished... :(

Which unit is the one to get? Heath? Kennedy? I thought I read the Heath unit has a slightly lower engagement temp than stock, so I guess that couldn't hurt for towing in warm weather?

[DmaxMaverick]

Jim, Thanks for the reply. Wow!! 165 degrees seems pretty low......

That's not the actual coolant temp. It is the temp of the air after passing through the radiator. If the clutch waited for 210

[88 K30]

That makes sense. I guess I was thinking the differential would not be that much. I tested this evening by covering the radiator with cardboard and revving the engine up for a couple of minutes to try and build some heat. The gauge got to about 210 (? - really hard to tell on the factory gauge) and the air from the fan was feeling pretty warm, but if the fan clutch engaged, it was not extremely noticeable. It might have increased in speed slightly while I was revving it, but it wasn't like it all of sudden started to howl. I guess that's a bad sign?

So what is the recommended replacement?

Thanks again!

[moondoggie]

Good Day!

For normal work, the replacement part available at parts stores is probably adequate. If you're at all concerned, look into Kennedy's clutch.

Blessings!

[DmaxMaverick]

Covering the radiator is good for getting the heat up there quick, but it won't diagnose a clutch problem very well. The air has to get to the fan clutch, and if the radiator is blocked, it won't (in enough volume). Once you get the temp up enough to be sure the stat(s) are open, remove the cover and the fan should come to life very quickly. If it's lazy, or AWOL, it's bad. The fan should engage, regardless of which stats you have, as the air temp will get high enough. Lower stats will engage the fan sooner, run shorter, and more often, all else being equal.