Why change poly-V/serpentine belt pulleys?
 

Think I got ripped off.
I just bought a very tidy AMG CL65 and thought I'd subject it to a full MB healthcheck as the car has not been used much in the past two years and only 35k miles from new.
One item thrown up as an "extra" during the B service was poly-V belt tensioner about £350 ??? so I agreed to that but suggested they fit a new belt while doing the job ( no labour) .
I get a phone call saying that the pulleys are a bit noisy and recommended that I have a new idler..I agreed. When I get the bill I see that they've fitted an idler, a belt, a tensioner, AND replaced all the pulley wheels.
I don't see any reason for that unless the new ones are improved design or the originals are broken. Seems to me they thought they could get the bill over $2000 that way.
Anybody have any views I'd be pleased to listen.

This is the wrong section for your vehicle but you sent it to get inspected by MB, what did you expect? The only time a dealer will EVERRRR touch my car is for recalls, and I'd think about it even then.

FYI... Poke a hole in the top of a water bottle - allows for a bigger stream. But...

It sure seems that since the only thing you are bascially messing with is the belt, and the sound changes (doesn't matter if it goes away or gets louder, the main point is it changed), that the belt is the issue. I forgot to mention this above, but from my experience, a quick chirp is a belt issue, while a longer lasting squeal is a pulley bearing. The chirp may go on for a period of time, but it has more of a very distintictive "on/off" pattern.

If you call or, better yet, stop by a Merc dealer with your VIN, they can look up service history. Of course, that will only tell you service that has been done at the dealer. But it may give you more info - and you ask them to print it out for you.

If I was in your shoes, with the info you have at this time, I would probably do the belt and the tensioner, as well. I'd chalk it up to "worst case, it's good PM and now I know when things have been done".

I hope OP has it all figured out since he posted this thread 6 years ago. :rolf: