120,000 miles? Check your serpentine belt pulleys!
 

Hi Peaches,

Over the last four years I have bought a W202 C280, a W210 E430 and a W220 S600. Experience with the first two is guiding my preventive maintenance choices. I just changed my serpentine belt and all of the pulleys on the S600 at 125,000 miles. The belt tensioner felt coarse and rickety turning by hand; was going to fail sooner than later and the other pulleys were aged as well.

The belt tensioner failed and shredded the belt on a trip to New Orleans in the C280 a few years ago at about 12X,XXX. The same thing happened last year when my wife was getting groceries in the E430 that had about 12X,XXX miles.

I am not going to get stuck somewhere because of a belt getting shredded when a pulley fails this time. If your car has 120,000 or more miles on the original pulleys, it would be worth your time to remove the belt and check all the pulleys and belt tensioner. Replacing a belt and pulley(s) in your garage, at a time of your choosing beats a cold rainy day on some deserted road or highway! It is also less expensive to shop around for parts and choose from good alternatives instead of needing them on Sunday in the middle of nowhere when I was willing to pay anything to get home.

http://www.peachparts.com/shopforum/...1&d=1425336752

Thank you Peaches for sharing your wisdom with me over the years. I hope I can pay it forward by telling anyone who is curious about this expected failure that can be averted.

Best regards,

Jeffrey

I've been recommending to my customers to change them anytime after about 150k on MB's and 110k on BMWs. 121k is lowest I've heard of em failing and will adjust my recommendations accordingly. Thanks

The idler pulleys on the M112 and M113 engines all show stress cracks (usually on the obverse that you can't see!) in the plastic shoulder surrounding the bearing by about 90,000 miles. I would definitely not wait to 120 or 150, particularly as it's a $20 part. The tensioner is a different story.

Carry an extra belt in the car. I do this with radiator hoses as mine exploded once while I was on the road. Had to purchase a random hose from a truck shop and make due until I got the right part

My recent experience has been that a failed pulley or belt tensioner is usually the cause of shredded serpentine belt. It is a good part of the maintenance plan to inspect belt. I would not have thought about checking the pulleys until recent experience.

It might be a good idea to check starting at 90,000 miles as suggested above. Looking at them would show stress cracks in plastic. Removing the belt and spinning each pulley and belt tensioner by hand will give a feel for the bearings. The only way to know the condition of items that are known to fail is to check and test.

The only fly in the ointment is that the stress cracks seem to develop on the obverse side of the idler pulley, which means you have to remove it to inspect it (it will still pass free play and spin tests). That's not an awful chore on the M112 in certain chassis (indeed, I changed that pulley in my car in less than five minutes, and I didn't even have to remove the belt), but on some it's a painful process. Besides, for $20 every 90-100K miles, just change it. :D