20swrt

My serpentine belt failed again at 98k miles. The first was at 34k. Second was about 70k. So averages about 30k each time for my OM642. I find that unacceptable. My Japanese cars last 100k and never gets me stranded, unlike my 2007 ml320 CDI. I notice it happens when its very hot - i.e. summer. All using Contitech 8PK2035. Dealer installed 34k. Others I did myself. Sourced from autohausaz. This time Im trying Bando brand 8PK2040. I replaced the tensioner at 70k. I have not replaced the 2 guide pulleys yet - they still seem to be smooth running.

kajtek1

Well ,,, it depends.
I drive cars long enough to remember in the past replacing belts every 20,000 miles.
Than in last years, although I don't keep vehicles that long, I believe couple of them had factory belts at 200k.
Quality of belt has huge value. When I was doing head gasket on 603 engine at 297k, I decided to replace old belt, showing some cracks as well. New belt from reputable indy warehouse lasted ..... 200 miles (less than two hundreds) till it turned into strings, so the old belt went back for some time.
I did carry spare belt on my Ford Powerstroke for 100k miles and sold the truck with 300k on odometer and spare belt still under the seat.
So bottom line - when good quality belts can run for 20 years, the cheap can disintegrate in days.
Inspect, inspect, inspect.

20swrt

When you say "factory belt" you mean the belt that came from the factory brand new right ? Unfortunately i bought it used at 32K so i dont know what brand that was. But at 34K, the dealership replaced it with Contitech and my assumption is that it is OE/OEM. But that only lasted until 70k. What do you consider better quality than Contitech for Mercedes ? Im hoping folks here can chime in how long their belts last and if they know the brands they use. Here's a picture of my last belt which frayed on both sides. The middle 6 ribs look good - not even cracked. Being used to Japanese cars - I want to have an idea if this is considered "normal" MTBF range for the OM642 diesels.

kajtek1

I think Good Year belts come with lifetime guarantee, so you might want to research the brand.
Beside mentioned bad experience with new belt, I never was forced to replace serpentine belt and the spares I bought usually come from dealer.
Yours wear premature, so next time keep en eye on replaced belt. Once you see strings showing on sides, take it back to the seller.
Additional experience I had - wife E320 is 3 years with us and last year wife walk home after the belt come off. Turn out idler puller bearing froze and kicked the belt out.
Belt was replaced shortly before we bought the car and was so good that it melted the plastic pulley with drops of plastic all over engine bay.
The belt had so sign of damage and is still working today.
Bad part about rubber is that there is no way you can determinate quality by looking at it.
I can tell quality of steel by the sound it gives when tapped. I can tell quality of plastic very often by the looks.
When it comes to rubber, you have to put it to life test to tell.

samaritrey

I wonder if something is not aligned properly and is causing the premature wear? My OM642 has the original belt as far as I can tell and it is at 124,000 miles. Probably should take it off again soon and inspect all pulleys though.

20swrt

Yes I think you may have found the culprit. One of my plastic pulleys (lower) have some plastic sticking out from the previous belt failure. At first I thought it was really like that by design but comparing it with the upper plastic pulley - it realized both are supposed to look the same. How do you remove/replace this pulley ? Is there a trick to remove the plastic cover ?

kajtek1

The idler pulleys are not serviceable. You have to replace whole thing.
The latest bearings MB is using don't have too good records and pulleys are consider maintenance item.
On old diesels they would run million miles.

speedyunk

Sounds like you might have a oil leak if ot wears out your belt that quickly.

If there is even a very tiny oil leak that drips on the serpentine belt it shreds it to pieces in a couple of hundred miles so i suggest you should check for any oil leak on your engine.

20swrt

Its definitely not oil leak coz i watch it constantly - the belt is bone dry. I've had that oil leak problem before 36k miles (dripping from the intercooler joint). But that has been fixed.

I replaced both pulleys and inspected every pulley for obstruction/alignment. The first sign of failure is a ticking sound bec the belt was fraying at the sides and stray threads were causing the noise. I need to watch out and cut those stray fibers as soon as they begin to show.