Chasing down a squeaky M104.980

[John5788]

I've been hunting a squeaking sound from the front of my M104. I thought it was the water pump and I replaced it only to find that the squeak persists. The squeaking sound is very loud at cold start up, but once the engine hits operating temperature, it quiets down to a small chirp and eventually silence. Applying throttle expedites this process of quieting it down.

The engine serial # is 12-022483 and according to EPC it needs a 2445mm belt. This leads to my first question, what's the difference between the 2 cutoffs that change the belt size from 2415mm to 2445mm? Maybe I'm running the wrong belt length because of the parts I'm using?

Without referring to the belt tensioner indicator, how do I determine if the belt is too loose? The tensioner says it is adjusted correctly (pointer at largest part of the triangle), but maybe the tensioner has failed early? The tensioner is only a year old as is the belt.

Any other ideas? It's not the idle pulley by the exhaust side. I already replaced that with a brand new fan bearing bracket.

[optimusprime]

Serpentine belts have groves in them ,some seven,, some more or less .Important that the belt is in the groves along with the right number of groves on the belt. Check if it is the belt by putting talk on to the belt it will stop making the noise if it is .It will make a mess on the engine if you use talk. Try water its easy to apply and will dry off after time.put a little in a spray bottle .Then spray the belt .

[Sugar Bear]

Possibly the shock/damper at the belt tensioner. Try prying it tight to see if it changes the sound. Also use water as mentioned on pulleys one at a time.

Good luck!!!

[John5788]

I continuously sprayed water on the backside of the belt (non ribbed) from top by the power steering pump. Within a few seconds the squeaking stopped and then came right back. The only places I'm aware of that uses the backside of the belt is the cooling fan pulley and the belt tensioner.

I sprayed some water around the fan pulley area and the mist stops the squeaking sound so its definitely coming from that contact area.

Looks like this Contitech v-belt I got went bad in less than a year, maybe time to try a different brand? Gates? Dayco?

Belt ribs look fine and there aren't any cracks anywhere though.

[97 SL320]

The problem isn't the belt ( If your tensioner is working . ) , it is the flat pulleys becoming glazed.

A new belt will stop the noise for a bit but once the back polishes a bit the noise will return.

The fix is to roughen up any flat pulleys with 80 grit or so. This allows the belt to be gripped rather than sliding across the surface. When the engine is running, the belt tends to walk across the pulley causing the squeak.

I've also found that the part number sticker can be slippery enough to cause squeak, sanding this a bit makes the noise go away.

Also, never ever use belt dressing. It goes on sticky but soon drys to a slick , polished nearly impossible to remove mess that will increase noise.

[John5788]

I'm going to replace the belt anyway. I went to the local auto parts store and bought the Gates belt with part number K060962 which interchanges with 6PK2445 according to their website.

But while I have everything off, I'll scuff up the fan pulley surface with some sandpaper and report back later this afternoon.

[97 SL320]

Sand all of the flat pulleys not just the fan.

[John5788]

Success, no more noises!

New belt:


Glazed pulley surface:


Sanded down with 120 grit:


I didn't sand down the belt tensioner pulley since it isn't old. I doubt it had any time to glaze over unlike the fan pulley which is probably the original and has seen multiple belts in its lifetime.