Screeching sound from drive belts at startup

[MaximaGuy]

Just changed the serpentine belt on Highlander. The screeching sound is getting worse and not sure what next to look for. I don’t hear it from the timing belt ( replaced them and the pump 100K miles ago) although I could be wrong.

Anyone experience this on a 3.3L Toyo and possible things to look for to isolate the culprit.

 

[paulo57509]

I've never heard a serpentine belt screech like a v-belt. doesn't mean it doesn't happen.

Did this start after you replaced the old belt with a new one? Or was it always there?

It's either the belt or the tensioner is weak?

 

[MaximaGuy]

The squeal was there before replacing the belt although the new belt is squealing more. I shall check the tension on it apparently it should dip no more than 3/8”.

 

[paulo57509]

Some tensioners have a wear gauge of some sort.

It may also be one of the accessories - alternator, water pump, idler, etc.

 

[D60]

I don't wanna stir the hornets nest, but if no accessories appear to be at fault try a few dabs of silicone grease on the belt.

Sorry.....[ducking]

 

[slacktide_bitog]

Either the belt is shorter or longer than it should be, or the tensioner is bad, or something driven by the belt has a bad pulley

 

[JMJNet]

IIRC, that one have a separate short belt.
So, there are 2 belts.
On that short belt, I had to use Mitsuboshi Belt (that is with an "o" not "i").
The squealing stop.

This is of a memory of a 2004 Sienna 3.3L sold in 2017.

 

[Bailes1992]

Any contamination on the pulleys?

 

[mattd]

You sure it’s not the adjustable PS belt making the noise ? IIRC these both have mechanical adjustments. Did you get them both tight enough?

 

[Boomer]

D60 called it correctly. I have done this MANY times for my friends who have this issue. Put a small dab ACROSS THE RIBS in about three or four locations on the belt. Make sure you use silicone grease.

 

[atikovi]

I don’t hear it from the timing belt ( replaced them and the pump 100K miles ago) although I could be wrong.

Well, it's time to do that again now. Take the serp belt off and run it to see if the noise is still there. If so, probably timing belt related, if not, check all the things the serp drives.

 

[Snagglefoot]

Twice, I tried to diagnose screeching sounds, suspecting pullies and the power steering pump. Both times is was the alternator. A new one took care of the issue.

 

[Trav]

+1 on checking the belt tension. I am not a fan of Silicone, WD40 or anything else on the belt, sure it makes it quiet but it is slipping even worse only silently, you can see it easily with a timing light. Look at the markings on the belt or use a chalk mark and look at it with the engine running, a belt that does not slip the mark will stay stationary a slipping belt will move around.

 

[MaximaGuy]

One other thing I stopped tightening the tension bolt the moment I experienced push back. Anyone remember to turn it one or two full turns after pushback from the bolt.

The alternator was probably replaced with a Denso reman some 60K miles ago - what a PITA it turned out to put that long screw back in. Its a Denso reman so doubt it is the problem, I will try the caulk test and then get the belt off and check for sounds. I know its the belt since the sound is more but as y'all said there is too many moving pieces out there. Isolation by dividing up the problem stmt is a real PITA.

 

[MaximaGuy]

I love the newer vehicles that has a spring loaded pulley to set tension correctly and auto-correction as the belt wears.
This whole tension bolt nonsense is poor engineering in my opinion.

 

[The Critic]

Are you sure the belt is tight enough?

 

[incognito_2u]

How old is the tensioner? On my 2006 Corolla, I replaced the serpentine belt thinking the squeal was from that only to find out it was from the tensioner not putting enough pressure on the belt causing it to squeal. Especially on start-up or when damp/rainy out. Further, I’ve heard of issues where the tensioner is proper, yet the bearing on the tensioner pulley was defective.
Side note: I used a serpentine belt called “Gatorback” and have had no issues with it.

 

[2strokeNorthstar]

One other thing I stopped tightening the tension bolt the moment I experienced push back. Anyone remember to turn it one or two full turns after pushback from the bolt.

The alternator was probably replaced with a Denso reman some 60K miles ago - what a PITA it turned out to put that long screw back in. Its a Denso reman so doubt it is the problem, I will try the caulk test and then get the belt off and check for sounds. I know its the belt since the sound is more but as y'all said there is too many moving pieces out there. Isolation by dividing up the problem stmt is a real PITA.

Too loose if you stopped at any tension. A good guess test is try to twist the belt. If you can get more than 1/4 turn, it's loose. Compare with an auto tensioned one.

 

[tessaseveride]

If a dab of Sil-Glyde on the belt doesn't cure the screeching, take a mirror on a swivel stick and look behind the alternator pulley. If there's rust there, that's the source of your screeching. You can purchase the pulley separately and bolt it right on.

 

[doitmyself]

I don't wanna stir the hornets nest, but if no accessories appear to be at fault try a few dabs of silicone grease on the belt.

Sorry.....[ducking]

It seems counter intuitive, but I also have had it work. The silicone conditions the belt to make is slightly more grippy. You don't slather it on. However, I view it as a stop gap measure to temporarily rectify some other problem. And, it should not be necessary on a brand new belt.