Hello,

I have a 2011 C300 and I’ve been chasing an issue with my serpentine belt squeaking usually when it’s cold outside and it will go away after 5 minutes of the engine running. I started noticing now that it squeaks even if the temperature is like 86 degrees Fahrenheit and will make noise all the way until engine operating temperature. I changed both the idler pulley’s, tensioner with febi bilstein, and a continental drive belt which I got from FCP Euro back in 2021. Since the replacement of these parts, no issues or noises were noted until 4 months later when in cold temperatures my belt started to make noise.

I had changed the belt and the upper idler pulley again and the issue went away for a while. Then it returned and I had it dropped off at Mercedes independent mechanic who looked at everything and he advised me that there is nothing wrong with any of the pulleys and there is no play. He told me to try installing a Mercedes OEM belt and see if it solves the issue. I give that a shot and it fixed it temporarily and then it returned. I saw the TSB’s that Mercedes issued about this issue and I noticed that my drive belt was the 2392mm that on my car at the time. I installed spacers just like the tsb instruction and that made the belt squeal like hell when the engine reved up to 2K RPM. I took that spacer off and then tried the lubricant and again it solve the issue until the lubricant dried out. When spraying water on the belt it will quiet it down too.


I ordered the 2397mm belt thinking maybe the one I had was slightly shorter. Before installing the new belt, I checked all the pulleys again and no defects noted. I cleaned all the pulleys and installed the new belt and drove like that till now with about 4k miles on the new belt. It’s starting to squeak again. I happen to see the belt slipping on the lower guide pulley because the black paint was wearing off on it.


Currently, I have INA idler pulleys and febi bilstein belt tensioner and OEM Mercedes belt. I am thinking maybe the belt tensioner was is not putting enough tension on it after the new belt stretches a little bit. I am considering buying the gates belt tensioner and trying that but just wanted another opinion. I am so sick of this issue and want it fixed. It’s usually a belt chirp but if I turn the steering wheel to lock it will squeal consistently.

 

Can you hear it inside the car with the windows closed?
You have changed idlers and belts, so the problem is not there. Water spray resolves it, so it’s belt squeak. It could be a rough or rusty spot on the pulley of one of the components, alternator, power steering, aux air pump, or even the crankshaft pulley. A rough spot on one of the pulleys will abrade the belt, causing it to “sing” after it wears in. The water pump is probably driven by the flat back of the belt, so probably not the cause, but check anyway. A wire brush and a lot of “elbow grease” are about the only way to solve a rough spot on a pulley because I don’t think you’re going to replace a major component for a squeak. Don’t use belt conditioner or dressing because it’s not meant for serpentine belts and makes a sticky black mess everywhere under the hood.

 

Which TSB do you mean exactly that was supposed to address the issue with spacers? Paste the doc or link to it here.

Speaking of spacers though, the grooved pulley has one, and is often missed on installation or removal, leading to a misaligned belt track either way. Is this what the above TSB was referring to?

 

I have a 2010 C300 4matic with M272 engine. Awhile back the belt and tensioner looked like they were bouncing so i replaced the belt, tensioner and grooved pulley. I just recently replaced the smooth pulley for no other reason than maintenance, actually i'm upset I did replace it since the old one looks and runs fine.

My Operators manual says "Poly-V belt 2401mm". I bought and installed a Continental 2404mm and it fit great. I bought the gates brand tensioner and it ended up looking exactly like the Mercedes tensioner i removed from the car, the Mercedes tensioner was even stamped Gates on it. For the two idler pullies i bought INA brand. It has been running great, no noises. When I recently replaced the smooth idler pulley I noticed there is a washer on the back between the pulley and the engine, good thing I was paying attention of i would have dropped it.

The only bolts i replaced were the grooved upper idler pulley since it came with new hardware. I re-used all the other bolts.

Heres the exact parts I used:








heres the washer on the lower smooth idler pulley"

 

Thanks for the reply. I can hear it slightly with the windows closed and the engine is idling. The belt doesn’t look like it’s abrading or getting damaged from hitting the edges due to a misaligned pulley or anything. If I put a brand new belt on it, there will be no noise for couple thousand miles before the noise comes back again. I checked all the pulleys for play and any damage but I didn’t find anything. However, I can see the black paint of the smooth idler pulley is wearing off and is definitely showing signs of slipping. My guess is that once the belt stretches enough the febi bilstein tensioner is not putting enough tension on the belt. It is a chirping noise but I noticed that when I turn the steering wheel all the way to the lock, it will squeal.

 

Tim c300,


I have a febi bilstein tensioner and both idler pulleys are ina and have changed the idler pulleys multiple times and it fixed the issue temporarily. I have tried putting a spacer behind the smooth pulley just like the tsb told me to. Attached are the two different TSB’s Mercedes issued out to address the problem.

https://static.nhtsa.gov/odi/tsbs/20...95946-5448.pdf

https://mbworld.org/forums/attachmen...9041_ver_2.pdf

 

I don’t think I have that washer behind my lower smooth pulley. I did place a spacer behind it per the TSB and it made the belt noise louder when the engine reved up.

 

I just installed the upper idler pulley as how you see it in the picture. Am I supposed to remove the black plastic you see in the picture before installing the pulley? I don’t have a washer behind it.

 

Squealing sounds like slipping. Maybe the Gates tensioner has a stronger spring, but that’s only a guess.
I don’t have the same engine, so I can’t address specifics.

 

That plastic thing stays, no problem. If you remember the old washer coming off with the original pulley, then you’re good. I have no ideas beyond this.

 

Do you have the M272 engine? I noticed on mine the oil filter housing hangs over the belt and if its leaking oil/coolant that oil can easily drop down onto the belt.

 

(tensioner + idlers + belt) kit all at once
See post # 4 by @TimC300

 

Hi. The squeaking might be coming from contact between belt and steering pump pulley. If it was replaced it with non OEM pump, for sure it comes from this part.

 

I came across something about the grooved upper idler pulley that explains the plastic spacer that comes with it:

 

thanks for that information. I pulled the old tensioner out and noticed that it was a gates tensioner even though I purchased the febi bilstein part from FcP Euro. I installed the new gates tensioner and everything was good until last night I heard the noise a little bit when I put my ears right next to the grill. I also noticed when removal of the tensioner that the edges of the belt is slightly frayed which means it is not aligned. I know for a fact that there isn’t a spacer behind the grooves pulley other than the black plastic part. There isn’t a washer behind the smooth guide pulley either.

 

The photo for the Febi tensioner does show a Gates tensioner, probably just repackaged. Sometimes when I look up Mercedes parts i can see the manufacture stamp on it in the photos, example looking for thermostat housings I see the Mercedes thermostat is stamped Whaler.




When you bought the new grooved pulley it should have came with a large washer on the back held in place by the black plastic spacer. I do not remember a seperate additional washer, I do know in my head that the grooved pully comes with everything to replace it, and the smooth pully just comes with the pully and I re-used the hardware.

For the smooth pully I dont see the washer listed in my parts diagrams. I got lucky and I noticed it installed. I've had the smooth pully off before when I replaced the oil filter housing gaskets, I think i got lucky that time also and either noticed it still stuck to the engine or i didnt even notice and it never fell off, i cant remember. I do know when I recently replaced the smooth pully I took that photo of the washer installed on the back, between the pully and the engine.







When i got done replacing the smooth pully I remember looking down staring at how the belt aligned and was sure I had the washer on the back installed properly. Maybe when you removed the smooth pully you didnt notice the washer and it feel off? I'm curious if other people have that washer in there M272 engines?

I went out and put a straight edge against the smooth pully and the crank shaft (*water pump pully maybe?) pully and they seem to line up. Not sure if this is a good way to check, but they appear lined up together to me. The belt appears to be centered in the smooth pully. In the photo you can see some of the belt threads are showing, i think this is normal. Ive had this on for awhile and dont see any issues.





I also checked the tensioner and the belt seems to be tight, its still at the beginning of the gauge with the 6PK2404 belt.

 

I watched a youtube video and this guy doesnt appear to have a washer on his smooth pulley. So I dont know why mine does to be honest.

Reading the Pelican Parts article on replacing the idler pulleys they dont mention the washer, though i wrote a comment about finding the washer on mine previously.

 

thank you for all that information. I just don’t understand why my car is making the chirping noise. It all started after changing the belt tensioner and the idler pulley as well as the belt back in 2019. I know for a fact that when I replaced my smooth pulley there was no washer behind it.

 

Maybe you can use a stethoscope to pin point where the noise is coming from. I bought an inexpensive one and it does work pretty good. It can pick up inconsistent noises like ticks and clunks, probably squeaks im assuming. When I put it on the grooved pulley bolt it was quiet but when i put it on the smooth pulley bolt it sounded loud, reminded me of the bathroom sink turned on. So I replaced the smooth pulley and the new one sounds the exact same so i think its just normally louder. It wasnt a grinding sound, more like a consistent "shhhhhh" just loud in my ears.



You mention the squeak when turning the steering wheel, have you checked the power steering fluid level? I recently checked and replaced my fluid. In general I think it should be changed every so often. I did it the easy way, suck some of the old fluid out and replace what I removed with a large syringe. I bought a 1 liter container of fluid and did the procedure once a day until i went thru the container.





are the bolts for the tensioner and pulley on tight enough. I have 35nm for the tensioner bolts and for the idler pulleys i think i used 25nm (follow-up operations).

 

Yeah, I have torqued all the bolts to the proper spec. I have also put a screw driver on the end of the pulleys and listened to it and it sounds great. The power steering fluid was changed I think 2 years ago with oem fluid and the level is good too. I used to have the belt squeal whenever I turned the steering wheel to full lock when I had the old tensioner in. I have tried it with the new tensioner. I will update you on that. The problem is that whenever it’s cooler in Chicago and I start the car, it will chirp and it won’t quiet down until the car reaches operating temp. Then it’s completely quiet. That tsb about pulleys shifting during cold temperatures makes sense but it didn’t fix the issue with the shims at least with the old tensioner in.

 

While looking around in the engine bay today, I noticed that the belt is running very close to the front of the lower guide pulley and there is about a 1 mm gap between the back of the belt and the rear portion of the pulley. Is that normal? It is seated properly on the water pump pulley however.

 

Hello,

I put a straight edge on both the pulleys and with the naked eye everything seems like it’s lining up as it should. I have some pictures that I will attach. As you can see in my picture, the belt is running close to the front part of the smooth pulley and there is like 1 mm gap at the back. Idk if that is normal. It does look centered on the water pump pulley grooves.

 

I wont have my car until Monday so I cant check mine. But from my photos it does look like there is a small space between the front face of the belt and the front leg of the smooth pulley. You can remove your smooth pulley and look for any abnormal wear on the inside face. On my old smooth pulley i did not notice any abnormal wear. But then again i do have that washer installed on the back of the pulley.

Where does your tensioner marks line up? Maybe take a photo, like i posted of mine above. It should be within the two guide marks.

What exactly do you have installed for the grooved pulley? because you mentioned some spacer in a tsb.

Post #5 you mention black paint rubbed off the smooth pulley, do you mean its worn off on the smooth surface that the belt rides on? Because that is normal, can see the pain worn on my old pulley as well.

 

OP in that smooth pulley, is there a washer between the bolt face and pulley? I have a washer in that position if I recall, but it's on the inside.

 

I have a washer on the smooth pulley, its on the inside between the pulley and the engine. Strange that I do not see this washer on any parts diagrams though.