alx

so when a few trucks of the same vintage start coming in with the same issue within a short period of time- i start to pay attention.

got more than 5 years on your truck? beyond 75k miles? you notice your idle is a bit high (750 on the om642, close to 900 on the gasser) on a regular basis even when the engine has reached operating temp? your battery is good? check your serpantine belt pulleys, dont forget the tensioner- one or more of them is in the process of seizing and is slowly stretching the belt resulting in undercharging condition. complete belt and offending pulley failure would follow up shortly- usually within 100 miles. i saw five (5) 2012s with the same failure inside 6 months. a few more of older vintage.

you have been advised.

BlownV8

Thanks for sharing!

kombifan

Thanks. Could you give some advice?

I have replaced 3 central pulleys in 2 years, the most recent less than month ago.
I've also replaced the belt twice, the other idler pulley twice now and the belt tensioner as well.
Just recently also had oil separator and valve cover replaced.

Does anything come to mind that woild cause this high rate of failure?

I'm in your mileage range. 95k. 2010. Always serviced at mb.

alx

assuming oem parts - something is definitely going on with your belt-train (lol). such an accelerated wear rate is not normal.

what you can do is run the truck for a while. stop engine. check belt temperature by hand (careful). if you can hold it with you bare hand- it is good. if too hot to hold- bring the truck into the dealer and ask them to perform an accessory resistance test - check all accessories (alternator, ac compressor, ps pump) pulley for excess friction as one of your accessories is slipping its pulley-to-belt contact causing unwanted friction and raise in temp.

my guess though is you have one or more semi-frozen pulleys.

kombifan

Thank you Alx. Yes all genuine mb parts, the extended warranty covers it all.
I did ask at the time if there was anything out of the ordinary causing any acellerated wear; but was reassured everything was normal.

I'll definitely check what you said and ask them to perform that test.

Thanks again.

sak335

Alx, I was actually looking through the maintenance schedule today trying to figure out at what mileage I was supposed to just throw a new belt on there, but as far as I can tell, there isn't a recommended replacement interval. The schedule just says "check" the belt every 10k miles or whatever.

So I guess you're saying that 75k miles is a good time to change it. Do I just check for play on the pulleys to determine if they need replacement? If they're not that expensive I may just proactively change them as well and keep the old ones as emergency spare. I just turned 70k miles this week and performed the normal 70k service so I guess I can plan on ordering parts to do this all on my next oil change which is about 5k miles off.

kombifan

So I drove the car and went to feel the belt and the temperature is warm to the touch. It's not too hot to hold.

Yup497

For what it's worth, I use to work at a oil change/tires/brakes type of place.

Most recommendations from auto manufacturers is if there is more than one crack per inch on the belt, change it.

alx

maybe you are just the unluckiest person on earth... maybe let it be and if it happens again ask them to check all pulleys and accessories for excessive drag..something aint right there.

on pulleys - check belt at tensioner pulley - it bends the belt "backwards" so you can see if it is cracked. generally if you have any cracks it is time for a new one.

kombifan

Hey alx,

i brought the car in this morning to have them check the belt train as the squeaking noise from the engine bay and pulleys came back again.

I asked them to perform the accessory resistance test and mentioned that the belt area around the alternator pulley was extremely hot. My sa was unfamiliar with the accessory resistance test though.
Anything else I should have mentioned?

Thanks again! 🙏

kombifan

Update:

Car is still at dealership.
On day 1 the mechanic had left early and hadn't updated his notes for my sa.
Day 2: mechanic heard the squeaking noise on startup but noise did not stay long enough to track down fault. Reported back that they would try again Tom with a proper early cold start.

🤞

kombifan

Update #2:

Car is still at the dealership.

Service Advisor told me that on Wednesday one tech could hear it, but couldn't trace the squeaking in cold start up; and that the following day the shop foreman couldn't trace or replicate any noise.

I asked for a ride along, and when I went to start up the car with the master tech; the car squeaked and squealed extremely loud....before disappearing again when warm. Master Tech corroborated the squeaking story to my sa....who then started to grumble that his techs are taking more than 4 days to find a squeak.

The master tech said he would report to the tech who was assigned to remove belt and try to turn the pulleys by hand, and would ask the tech to listen on cold start up with a stetho to track down which pulley is at fault. He suspects bearing are shot from within.

Alx. Anything else I can mention to the techs and sa?
I have mentioned to them that the belt felt extremely hot around the alternator; and that ( twice, 2) idler, (3x) central pulleys and tensioner have been all replaced.

Have also mentioned the accessory resistance test..but was faced with a blank stare.

kombifan

Update 3.

Sa called this morning saying that they sourced it to the lower guide pulley which was replaced in february of 2018. No charge, as the benz parts and labor warranty is 2 years.....


But I have a feeling the original cause or underlying issue is still there......

Any advice and help would be greatly appreciated. I've been in a loaner since last week Monday...

kombifan

I've added the receipt, in case it sheds light for others who run into this issue.

alx

for the love of God just have them spin by hand all the pulleys and check for extra friction or play. it is usually the tensioner pulley...

kombifan

I did ask them to perform that on Friday when I did the ride along. The master tech assured me that would be done, removing the belt and spinning it by hand.

Short of standing over them or performing the work myself, not sure what to do.
Trust but verify doesn't really work here. Can't really verify if they do check it.
I have a brilliant extended warranty for this reason so it can be in the (hopefully knowledgeable) hands of a trained mb tech.