Loud Screeching Sound From Cummins 330 Engine

[Larry T]

Good Morning Everyone. Our 2004 Diplomat with the Cummins 330 is making a loud screeching sound intermittently when it's warming up. I would compare it to a AC compressor that is frozen and squeals when the clutch engages the compressor but it's several times worse than that and the AC is off. Is there another system that cycles on and off? I need to know where to start looking.

Thanks!

Edited September 10, 2023 by Larry T
change the year

[Dr4Film]

Larry, I would start by looking very closely at your serpentine belt and your AC belt making sure they are not too loose. Next, is to look for a bad bearing in one of the pulleys that are rotating when the engine is running.

Sounds like once things warm up and expand the screeching noise dissipates due to the expansion.

Edited September 10, 2023 by Dr4Film

[klcdenver]

Take the tension off the serpentine belt and try turning idler arm, water pump and all pulleys by hand to see if one is harder to turn than the others. If not this could be the fan drive bearing. To see if it is the fan drive bearing you would need to remove serpentine belt and start the engine, be sure and don’t run it to long and get it overheated.

If it is none of the above then it will probably the worst, a exhaust leak such as burned out gasket or a cracked manifold. When the the metal gets hot and expands the noise sometimes stops the leak somewhat. Look all around your exhaust manifold and turbo discoloremtent and streaking. 

[Larry T]

Thanks for the comments. I'll pull the belt and start there.

[strangebird]

I had that happen a loud screeching sound from the engine, turned out it was the starter not disengaging, the culprit was the key in the ignition switch was loose and if you wiggled the key the noise stopped, tow bill, $900.00 to the nearest shop 

[Larry T]

Thanks everyone - The issue was a loose AC belt, even though I just replaced the entire system. This was an easy and cheap fix which doesn't happen too often!