Belt(?) squeal under load but only when warm

Joined
May 16, 2019
Messages
15
Location
Singapore
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..?
 
Joined
Jan 22, 2011
Messages
5,837
Location
Ohio
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.
 
Joined
Sep 19, 2008
Messages
2,551
Location
Pennsylvania
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.
 
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Joined
Jan 13, 2013
Messages
4,161
Location
Texas
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 .
 

Calikura

Thread starter
Joined
May 16, 2019
Messages
15
Location
Singapore
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.
 
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