Hi

Yesterday, out of the blue, the truck while driving at speed on the interstate, started roaring. It seemed that suddenly the engine had a great load on it and was attempting to climb a large hill, none of which was the case.

I noticed that rpms were about where they usually were as were temps.

After thinking about it, the last time I saw this was in the 80's..and it was a fan clutch on my GM diesel.

My fan clutch has so much resistance stone cold that it can barely be turned by hand... I would consider it "a ton of resistance".

Is my diagnosis correct on this fan clutch? If so, is NAPA a good source of clutches?

 

It is somewhat normal for the fan clutch to cycle, especially if it is hot and the motor needs to cool down. When it cycles, you will hear the extra noise.

 

hi

this is way more than usual noise. sounds like a jet engine and sucks a lot of hp.

 

When you describe a "ton of resistance" that sounds like too much. If your fan clutch is locking up, you are right, it will sound like a jet engine when you are at highway speed. I therefore think you are correct about what is wrong. Yes, NAPA or most other part stores are fine. I don't think this needs to be a OEM part.

 

What happens when the engine has cooled a while? The fan should rotate with resistance for several turns and then free up somewhat. Normally these things fail where they do not lock up when they should vs the other way around....however it does happen, just uncommon.

Before you buy a new clutch, I would suggest you carefully inspect the radiator for blockage. I have seen amazing photos where pests will build a substantial nest of debris in between the coolers and cause the problem you describe. Worth checking out. The activation temp is around 212-215 degrees but you won't see any movement on your dash gauge.

When the fan locks up it draws about 25hp. It moves a LOT of air under those conditions.

 

hi

i checked the radiator and there is no obstruction. the fan is nearly seized. it will barely turn by hand and the operative word is barely.

what brand is recommended for replacement?

 

The fan noise you describe is just the way mine sounds. I will also get surging. I can't speak to the resistance because I have never check it... When mine first did it several years ago, I thought something blew.....

 

hi

the first time you hear it...it sounds like something catastrophic just happened. Its been almost 30 yrs since I last heard it, in a GM 5.7 diesel no less.