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The screeching happens only at high RPM's (2800-3000) and only when the radiator fan is running. Typically this would be when I'm climbing a long grade, in 3rd gear, and the fan kicks in.
I initially thought that it was the fan clutch, the fan bearing, or the tensioner pulley bearing, but I replaced each of these and the noise is still there.
I'd appreciate any and all advice.
Thanks!
-Mark
Last edited by msiminoff; 07-08-2018 at 03:25 PM.
Reason: Issue resolved
Sounds like your describing some belt squeal under heavy load...
I replaced the tensioner with a new (Cummins) one this past weekend and I replaced the belt a few months ago (the sound was there with the old belt too) with a Gates "green" belt.
What is the back side of that green belt like? I don't see many of them around this area, I deal mostly with OEM or Continental belts. This year of Cummins drive the fan on the back side of the belt, where most HD diesels drive the fan on the ribbed side of the belt. From what I understand the green belts are geared more towards that type (ribbed) of drive style, so I'm wondering if at that high load that green coating is just slick enough to cause some squeal. if you have a temp gun you can give it a good run with it squealing, then gun the pulleys, the one that's slipping will be hotter then the rest, and would give you a place to start looking.
The back side of the Gates "K081264HD" belt is smooth polyurethane (or similar plastic). It did seem to have a little bit of black residue on it so I just cleaned it with some denatured alcohol. We'll see if that makes any difference.
The rattle/squeal noise was there with the previous (standard Gates) belt, but wasn't there with the Green one before that one... or the OEM belt before that.
Yes, I have an IR temp gun. I'll be surprised if the noise is from slippage... the crankshaft and fan pulleys have a ton of contact area... that said, I'm willing to consider anything at this point.
My best guess is still a bad bearing in the serp' belt system (maybe the idler?) or a vibration resulting from the air-flow of the radiator fan.
Decent contact on the fan pulley, but still the back side of the belt, I always wondered why they did that. in most other applications the ISB runs a grooved side for the fan drive. at 2800RPM with the clutch locked up that is a LOT of stress on a smooth belt. Could be a bearing, I haven't heard the noise in person and it's not always easy to get a good idea of a sound based on a video clip, but if I had to bet I would say about 80% chance of some slight slippage based on described conditions. That being said, I did just change a water pump and top idler for bad bearings in my truck. With the belt off you should be able to feel any bad bearings as either a slight wobble or rough turning when spun.
Are you talking about when he turns the A/C on/off? I did see that, but since it's not actually the OP's truck, I was focused more on the noise then the actions.
You are missing something in the video posted above....
My truck makes the noise when the RPM's are above 2600 and the radiator fan clutch engages. It does this whether the A/C is on or off.
Originally Posted by StealthDiesel
Anytime you suspect a serpentine belt or belt driven accessory issue, remove the belt and fire up the engine.
Again, the noise only happens when the fan clutch is engaged... and I cannot reproduce the sound with the belt removed because then the fan doesn't spin
Problem solved! Tezcatlipoca, you were correct, the screech was the serp' belt slipping on the fan pulley... I think as a result of coolant residue.
I did a test by scrubbing the smooth side of the belt with ScotchBrite pad and acetone, then went for a drive. The noise was gone.
I removed the old belt (assuming the acetone bath wasn't good for its longevity) and thoroughly cleaned the surface of all of the pulleys (smooth and ribbed ones). I picked up a new Gates "green" belt and cleaned both sides with soap & water, then re-installed. I have driven ~1500mi and there is no belt noise at all.
Here's some back-story; I lost the water pump about 6K miles ago (~150K mi on motor). It leaked enough to have gotten coolant onto the belt and all of the pulleys. I replaced the pump with a new Cummins one, and put on a new Gates green belt too, but I didn't think to clean off the pulleys. After installing the new pump I still smelled some coolant... not sure if it was from the original pump, or a tiny weep from the new one as the seals seated. I didn't think much of it because the coolant level didn't drop noticeably and there were no puddles under the truck. Anyway, I am pretty sure the slippage was caused by the coolant contaminating the belt & pulley... maybe it allowed some dust to stick to it too.
On the plus side, I now have a new water pump, belt, bearings, idler, & tensioner.
Hope this helps somebody.
-Mark
I too had the same screeching noise when fan clutch engaged. I realized that my green gates belt was completely black. I had a power steering leak a while back. I took 150 grit sandpaper to the belt as it was idling. Easiest spot was under the ac pulley. Lightly sanding getting the majority of the glazed over ps fluid. Then used a rag with soapy water to finish cleaning the belt. Overall took about 10 min. Belt looks good as new. And no more squeal.
05-13-2018, 08:12 PM
