Belt(?) squeal under load but only when warm

[Calikura]

As per title - after engine is thoroughly warm from a long drive of over 30 minutes I get a squeal that sounds like belt squeal, but while it is very high pitched, it is not loud.. but well concealed by the otherwise normal engine noise. It's subtle enough I thought it was tinnitus messing with me at first, but when I have the windows down rolling through the quiet residential parking lot and listen carefully, it's there, and it stops when I let off the gas or at idle.

Cold start in the morning, and/or if I only do a short drive, the squeal is completely absent even under hard acceleration and with the AC on.

Checked the basics - no wobble of serpentine belt on pulleys, no wobble of pulleys themselves, none seized, no grinding noises and belt tension feels within spec. Engine has a timing chain rather than timing belt. Don't have any means of loosening the tensioner myself so I can't remove the belt to hand-spin the pulleys - will have to get that checked at the shop.

Is there something obvious I should know if I get a squeal only after thoroughly warmed and driven a bit? My past experiences with belt squeals is that they are worse in the morning or when it is wet.. so this one seems totally out of whack. Maybe it's not even the belt..?

 

[Lubener]

When it is warmed up, have a buddy rev up the engine to produce the squeel. Then give the belt a squirt of water and see it it quiets down that will isolate the belt.

 

[The Critic]

What is the application?
Does the alternator have a decoupler pulley?

 

[Boomer]

Over the years, I have used this trick over forty years to quiet numerous squealing belts that otherwise appear to be in good shape and still quite functional. Take a pea size lump of SILICONE (not petroleum) based grease and gently apply it to the ribbed or contact side of the belt. Do this in about three places along the contact side of the belt so that they are approximately equally spaced. Turn on the engine and let the car idle for a minut or two to allow the grease to be equally spread across the belt. This will NOT cause the belt to slip but will really quiet the noise.

 

[Kawiguy454]

Belt tensioner pulley bearing can also squeal when it starts going bad

 

[WyrTwister]

Originally Posted by Kawiguy454
Belt tensioner pulley bearing can also squeal when it starts going bad



Yep . The pulleys / tensioner bearings can squeal . I have also had the A/C compressor clutch bearing make noise .

 

[The motor guy]

Bearings make noise when they get hot

 

[The motor guy]

Had a bearing on my boat go bad and it would be fine for the first 10 minutes, then after that it would stall the engine.

 

[Calikura]

It turned out to be the tensioner pulley bearings. The spring in the tensioner was also creaking a bit. Thankfully, the crank, alternator and water pump pulleys are still good.

I replaced the tensioner, the idler pulley and the serpentine belt (which had 60k miles on it anyway). Things are quieter under the hood now, and even the subtle chirp I used to get upon first engagement of the compressor clutch in the morning doesn't happen anymore.

I admit the fact that the squeal only happening when thoroughly warm threw me off a bit, and I started to overthink a simple wear and tear issue.