will4iron

It started last December when we had a few days of freezing temperature.
Kind of scratching or squeaking sound came from under the hood when rpm is low OR wait at traffic light.
I just stopped by local MB dealer nearby and a tech dropped some special belt lubricant on belt and sound was gone. I was told that it can be happened when temperature changed and rubber belts act like that. Well whatever the reason the noise was gone so it seemed like a pretty quick fix.

A couple weeks later, the noise came back and I went back to the same dealer again with proper service appointment.
At this time I test drove with service rep and he confirmed the noise.
I left my 2011 E350 a couple days at the dealer.
2 days later service manager called me they couldn't duplicate the noise after I dropped off my car but they lubricated the belt with same special oil again that I had very first time.
He noted that this is a known problem to MB so he wrote some service numbers on service paper. (LI-13.20-P-049041-Performed apply Lube compound to engine belt cold and at high engine temp)
It seemed like they finally fix the problem.

However, several months later it CAME back again.
I was stuck in the middle of heavy traffic in S.F. and finally parked my car at the 5th floor of parking garage but while I was driving parking garage ramp at low speed I smelled sweet coolant smell but there's no noise.
After parked my car, I opened the hood and visually inspected engine room area to look for any coolant leak.
I also checked the coolant reservoir and surround of engine to look for any leak marks from coolant leaking but nothing.

Few hours later when I started my car then the same squeaking noise started. All the way from 5th floor of parking garage to the ground I continuously heard squeaking sound came from under my E350 hood.

It was sort of embarrassing moment to other cars behind or front of me because almost brand new white E350 Mercedes Benz continuously made that loud squeaking noise.

I suspected that this weird noise is related with coolant and serpentine belts.
After I drove about 30+ miles from that point, the squeaking noise was gone almost but I still can hear very minor squeaking sound when idling.

I called the dealer about this incident but they asked me to drop off my car again to be inspected but I knew that if there's no present noise when I drop my car then they won't do anything with it except applying more "Lube compound".

Please advise me.

jcsws6

I have the same cold start low rpm squeek. Please update when you find the problem.

ArcticE

Hey I just noticed the same problem on my 2010 E350 4matic sport. On cold starts I hear a loud squeeking noise coming from either one of the pulleys or the belt. The noise speeds up and slows down while accelerating and the squeak goes away entirely after about 30 minutes of driving. I just had a new thermostat put in by the dealer and just started hearing the noise (don't know if it could be related). Did anybody ever find the culprit or does anybody have a way to diagnose the noise? I will upload a video of the noise soon.

Thanks for any help.

konigstiger

Have the dealer revisit repair they should diagnose problem at no cost. Either problem will be corrected if related, unrelated – you will know what is causing the problem and can choose dealer, independent, or DIY to resolve.

ArcticE

Thanks for the feedback. I have a new appointment for next week I just rather try to find it myself because I hate putting my car in other people's hands.

Mud

Stop oiling the belt and replace it, it's glazed and the cold temps make it less pliable and prone to slipping/squeeling, easy DIY replacement.


Sometimes also the idler pulley bearing is also noisy but I would do the belt first.

ArcticE

Thanks. Never "oiled the belt" but have 45k on the car so might as well change out the belt and see if it stops. I will give an update when I do.

Arrie

Usually belt squeaking starts when the belt bottoms out on the driving pulley. This is either due to the worn belt, worn pulley or both.

If the noise started with the thermostat job then they may have have to remove something like the belt tensioner for access and could have re-installed it with not enough belt tension, which is the other reason for the problem.

It could be the first option and it just coincides with the thermostat change and colder weather. Cold weather makes power steering pump to turn harder and this could be the reason for the trouble at cold starts.

Check the pulley at the end of the crank shaft. If the belt is all the way between the flanges it is likely bottomed out. The V-belt carries friction by its sides wedged by the tension against the pulley flanges. When the flanges and belt wear enough the inside flat side of the belt bottoms against the flat bottom of the belt groove and the force at the sides is lost. This is when the squeaking starts.

If you see the belt outside flat side deeper than the outside diameter of the pulley flanges your belt probably is bottomed out.

Check the other pulleys too as you may have only one separate belt for the steering pump. This would mean both pulleys experience the same load.

Also the alternator pulley can be a problem but it should not really change with cold or hot start.

If you find worn pulleys you might be able to find a "fat" replacement belt. These are made to compensate for the worn pulleys.

ArcticE

Wow thanks Arrie for that good info. I will look into everything. Here is a quick video I took of the noise.

View My Video

LebaBenz

Same issue, I changed all my belts and the pully, then it was resolved, but now a few months later it came back. Did you resolve the issue? Or do you just lube them every time

Royce118

Hi, I know this thread may be a bit dated but I am experiencing the same exact sound from my 9000KM motor engine. Do you happen to get this sorted out?

LebaBenz

Hey royce, check your tensioner and pully (for me it turned out to be the tensioner)

Royce118

Thanks buddy. Car will be heading to the dealer on Thursday. Just wanted to find out more about the issue before sending it in.

will4iron

Since I visited the dealer twice in 2013, it seemed like somehow the belt noise issue was solved(maybethe belt was worn out?). I put another 20K after that without any noise issue. However, I had thermostat issue recently. The CEL popped up few weeks ago and I ran the error code reader and it said thermostat. it stayed open so engine consumed more gas than normal operation due to cold running. I brought my car to local European expert garage yesterday(4-8-2016) and got new thermostat installed. When he replaced my thermostat he replaced old serpentine belt and one of the small pulley which is located very top of the engine block. As soon as the belt was replaced, there's sort of squeaking sound came out of the belt but eventually it disappeared as engine gets warmer. Today when I cold started my car, even loud noise was coming out of the belt. it was way louder than yesterday so I dropped very little of WD-40 at the side wall of 2 pulleys bolts carefully and then the noise is reduced. Then I drove my car few miles to test it then the noise is totally gone but I am not sure whether it might come back or not later. I left a phone message to the mechanic who replaced the thermostat and belt since the shop is closed today.
Does that brand new belt need some time and mileage to be adjusted?

cetialpha5

The pulley could be misaligned. There's also the tensioner and there's another pulley that could be bad. There's no real adjustment you can do to a belt.

will4iron

I suspected that the other pulley
. it's little bigger than one the mechanic replaced and seemed like the noise is coming from it..well I dont know what to do because I didn't have any belt and noise issue before replacing the thermostat but now I have this.
Can I blame the mechanic who replace the belt and one pulley yesterday?

cetialpha5

You can blame anyone you like, but did he cause the problem? Probably not. It seems to be a wear item on the 350, search the old threads. If you took the belt off and spun it, you would be able to tell if it's good or not. There are various vendors that sell a belt kit which includes the belt, the tensioner and the two idler pulleys. My guess is that either it's misaligned or they were both worn so they had the same amount of play, now one is new and one is worn so they're no longer aligned.

will4iron

I agree with your opinion about one new pulley and the other old one. I should replace the other one sooner or later but still wondering why i habe this issue after someone touched my belt and pulley. BTW, mine has only 34k miles on it. Do you think the belt and pulleys can be failed at this mileage? Unusual I believe.

cetialpha5

That does seem somewhat low. Maybe lots of city driving? If you check the previous generation which is still the same engine, it's not unusual for them to go in the 60k range. I need to replace my thermostat too and will just grab a kit and replace it while it's all apart anyway.

will4iron

The 2nd day after thermostat replaced and it's weekend but there's chirping continues whenever cold start. I investigated where the noise is coming from and found something. It's lower idle pulley or lower guide pulley.

Here's what I did when the noise started,
First, I used a piece of soap block and used it on the one side wall of belt carefully when the motor is running... noise's gone.
Then I drove couple ten miles (actually I needed to pick up someone at the airport last night)...no noise at all..
Next morning which is this morning, Sunday, the chirping noise still there when cold started.
It wasn't squeaking but chirping noise.
I used the soap option again then the noise is gone. (That means the soap option is NOT permanent fix but once the engine is warmer then there's no more chirping noise at all)

I suspect lower idle(guide) pulley because the belt is sitting a little to outer side of pulley and there's about 1/16" of room left inner side of pulley.
Therefore, the side wall of brand new serpentine belt touches outer side wall of metal pulley (lower) so it makes noise especially when both metal and belt are cold I guess.
If it's the problem of any of pulleys bearings then it should make same chirping noise no matter I tried the soap option but the noise was totally disappeared whenever I used the soap option...
So technically, either MB designed the pulleys wrong way OR the mechanic tightened my lower(guide) pulley too much.
Either way, the pulleys are NOT aligned!

And that's why the MB dealer kept using the belt lubricant whenever I brought my car in March of 2013....and they knew this as "known problem".
The Belt and pulleys are just fine in 2013 and 2016 but pulley alignment's wrong.

In addition, theses incidents happened whenever I had a new or pretty much newer belt....

Mobkob03

Dear Will4iron,

Your correct!! I'm new to MB. I've spent too many years driving Honda, which has been outstanding, and also restoring old British sports cars, less fun. My cars friends would tell me go German. Last month my neighbor finally had enough with the belt squealing on her 2006 R350. I offered to look at it, did the research, changed the upper and lower idle pulley and installed a new belt. The squeal was reduced and then came back like I never changed it.

With close observation I found exactly what you have detailed. The squeal comes from the belt coming up from the water pump up to the lower idle pulley. The edge of the belt, towards the front of the car, rubs into the flange wall of the pulley. The rear of the pulley has 1/16 open space. The pulley is recessed or the water pump pulley isn't pressed far enough on the shaft.

While reviewing my pictures when disassembled I found the previous "mechanic" installed a washer behind the idle pulley in hopes to move it forward. Knowing this wont work I tried it anyway. It remove the squeal by moving the belt out of the water pump pulley by one track, but did re-positioned the belt on the idle pulley with equal spacing on sides of belt. Not a good idea. So I'm at a loss and agree it's a known manufacturing defect and is the result of pulley alignment. My neighbor is outraged by it since they bought the car new and babied it but it fell part around them. They've offered it me at an offer I can't refuse, and I really like the feel of the car.

I drove it to work squealing all the way and intend on buying it. I'll have to keep looking for a fix but its not replacing both idle pulleys, tension pulley, belt and a case of WD40. Already did that. by the way, thank you to all who have responded on this issue.

cetialpha5

I replaced mine recently with the conti belt kit on the W211 which I think is still the same engine as the 2011 W212. I can't remember now, but on one of the pulleys, it had a washer on it and the other one didn't. Maybe yours got swapped around. The washer didn't come with the kit. Just reused the existing one and there's no noise.

will4iron

I bet the washer behind of pulley method might fix this problem. Just move the position of tension pulley a little forward so there's more room inside of pulley. Ultimate goal is to make the belt won't touch the pulley wall. Just thought.

dweb4

Yesterday I replaced my belts and both grooved and smooth idler pulleys. All was good until this evening when I started the car and can hear squeaking noise from the belt. I checked both pulleys and the belt again after it warmed up still hear the squeaking. The new belt was a Contitech belt I noticed the new belt has a small web pattern on the back of smooth side and it appears to be making noise right where it makes contact with the smooth idler pulley. Just to see I put the old belt on and the squeaking noise is gone. The old belt is smooth on e back side no web pattern. Has anyone bought a new belt with web pattern on the back or smooth backing? Just wondering if I got wrong belt or should let new belt break in some more. Any help would be appreciated.