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1999 ML320 (sold), 2011 ML 350 4Matic
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Discussion Starter #1
Are there known chronic problems with the OM 642 BlueTec? I was considering a 2011 ML350 with 113K miles. It checked out fine except my mechanic "thought" he heard some noise on the cold start. Warned me that he had 2 customers recently with timing chain failures (at 140K) resulting in ruined engines. Is this a 1 in a 100,000 occurrence, or is this a lingering problem for BlueTec's approaching 150K mark? Does a timing chain failure always result in a blown engine?
 

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2015 VW Beetle 1.8l, 2014 For Escape, 2001 BMW R1100S. GONE 2009 ML320, 2001 C230K, 1983 240D
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277 Posts
Mine is a 2009 with 90k miles on it. I don't remember ever reading about timing chain problems with the OM 642. Considering they are in Jeeps and Sprinters there are a LOT of them out there. Swirl Flap motors and oil cooler leaks seem to be the most common issues.

The reason a chain failure would be an issue, is that when the chain goes, the pistons will hit the valves, diesels are high compression interference engines. A chain breaking would be time to buy a used engine from a salvage yard. I don't want to think about what a rebuild after a piston/valve issue would cost.
 

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2010 Ml 350 Bluetec
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8 Posts
just bought a 2010 bluetec with 112,000. Mint shape and maintenance records back to new. Thought i heard a noise at startup on test drive but could not replicate it. Heard it a few more times and investigated, timing chain is stretched. It wont always do it as it needs time for the oil pressure in the tensioner to leak out and release tension. If you look down though the oil fill hole you can see the tensioner. Run the car for a minute and shut it off. If you can see the shiny portion of the the tensioner the chain is bad. It will sound like a moderately loud ticking or rattle for about 3 seconds. Way more noticeable with the hood open. Any good shop will get about 3k to fix it. Ive been a lifelong Diesel Technician so Ill tackle mine myself but still need to buy a few hundred in specialty tools. Check the rear coil springs two, they are known to be broken near the mount. Was an awesome ride for the 400 miles ive driven it. Unfortunate now its a garage ornament! Saw you post and joined the forum just to let you know. I think there are a lot more out there than people know about as if you get in and shut the doors and start it you may never notice it till its too late!
 

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1999 ML320 (sold), 2011 ML 350 4Matic
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Discussion Starter #4
Thanks for the feedback! I better heed my mechanic's concerns.
 

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2011 E350 Bluetec
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41 Posts
If the slap is only heard for a few seconds when the tensioner pressure leaks out, then wouldn't that signal that simply the tensioner needs to be replaced and the chain itself is fine?

Also - on my 2011 E350 bluetec there is an annoying metal plate under the oil cap blocking the view of the chain and tensioner. Does anyone know if that is removable?

I have the 2 second slap noise at startup and intend to change out the tensioner this weekend. I'll report my findings. I'd be willing to bet that the existing tensioner is not holding it's oil and, therefore, allowing the slap until it's re-pressurized.
 

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2011 E350 Bluetec
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41 Posts
Well - I would not worry. Many things can go wrong with any car. It's my opinion that fewer things are going wrong with this car.

I just pulled 38 mpg on a trip to Michigan this past weekend. The timing chain is fine - except for those two seconds of noise that appears intermittently at startup.

My big question is, when I replace the tensioner, whether I should prime the new one of not. The Mercedes directions I have simply say to take off, put new one on (attached and for a W212 not a 164 although same engine).
 

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2015 VW Beetle 1.8l, 2014 For Escape, 2001 BMW R1100S. GONE 2009 ML320, 2001 C230K, 1983 240D
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Where did you get your new one at, and about how much? Might be worth changing next time I change air filters, since that is the most difficult thing to deal with. I hate pulling the filter housings...
 

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'08 ML320 CDI
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877 Posts
Well - I would not worry. Many things can go wrong with any car. It's my opinion that fewer things are going wrong with this car.
Yea, I'll just listen for any noises on startup, just in case. Seems completely quiet at this time. I definitely had my fair share of repairs on this vehicle; hopefully it's a phase and it keeps running without issues now. Very well maintained and only 73k mi but it doesn't seem to matter.
 

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2011 E350 Bluetec
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41 Posts
N41EF: It's about $116. Get the good ones - Hardly a part to screw around with.
 

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2009 ML320 BlueTec
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83 Posts
I'm little confused, the instructions R&R chain tensioner is posted here are calling to remove oil housing, that is on driver side, but your statement is stated that is it can seen thru the oil filler hole??? that is on passenger side. btw there is a big bolt goes inside the engine on pass side, you can even see and fill it, if going down and follow throttle body bracket.



just bought a 2010 bluetec with 112,000. Mint shape and maintenance records back to new. Thought i heard a noise at startup on test drive but could not replicate it. Heard it a few more times and investigated, timing chain is stretched. It wont always do it as it needs time for the oil pressure in the tensioner to leak out and release tension. If you look down though the oil fill hole you can see the tensioner. Run the car for a minute and shut it off. If you can see the shiny portion of the the tensioner the chain is bad. It will sound like a moderately loud ticking or rattle for about 3 seconds. Way more noticeable with the hood open. Any good shop will get about 3k to fix it. Ive been a lifelong Diesel Technician so Ill tackle mine myself but still need to buy a few hundred in specialty tools. Check the rear coil springs two, they are known to be broken near the mount. Was an awesome ride for the 400 miles ive driven it. Unfortunate now its a garage ornament! Saw you post and joined the forum just to let you know. I think there are a lot more out there than people know about as if you get in and shut the doors and start it you may never notice it till its too late!
 

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2011 E350 Bluetec
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41 Posts
As a follow up: I did replace the tensioner. When i removed the old tensioner it was clear that it was faulty - splurging oil out the base when pressed on. The 2-3 startup sound was gone but replaced with a more regular and consistent slapping sound. Further investigation (expensive investigation) found that, indeed, the timing chain had stretched. It's being replaced right now.

I have a theory. It's my impression that the tensioner initially failed - by leaking out the oil during period between starts and leaving the chain without tension. After starting the engine, the momentary re-tensioning (loud slapping sound) caused the chain to eventually stretch out. The inconsistency, during load, of the bad tensioner only made it worse.

As to what caused the tensioner to go bad? Either there was simply a bad run of them around late 2010 to 2011 or, perhaps more likely, the preponderance in the midwest of crappy B20 (20% biodiesel). It could conceivably be a contributing factor by what it leaves on top of the crankcase oil. Who knows.
 

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02 ML320 06 ML500
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When i removed the old tensioner it was clear that it was faulty - splurging oil out the base when pressed on.
The tensioner is supposed to be loaded with oil. The oil prevents the tensioner from retracting back inside itself. And I am assuming that it was fully extended which means that it could not tension the chain any further, hence the replacement of.

The posted instructions are faulty/incomplete. Watch the video below.

 

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2011 E350 Bluetec
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41 Posts
Well - two things:

1) that video is for the m272 engine. Which is a V6 gasoline engine and not the OM642 diesel engine that this thread is about.

2) The oil should hold in the tensioner. My tensioner, the one that I removed, was faulty for not holding oil.

For completeness - here is the timing chain replacement for an M272 (attached) which is a different procedure.
 

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02 ML320 06 ML500
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Well - two things:

1) that video is for the m272 engine. Which is a V6 gasoline engine and not the OM642 diesel engine that this thread is about.

2) The oil should hold in the tensioner. My tensioner, the one that I removed, was faulty for not holding oil.

For completeness - here is the timing chain replacement for an M272 (attached) which is a different procedure.
Your original theory was that the tensioner was faulty because when you pressed on it "it splurged oil". It is supposed to work like that.

Secondly, if you look at the top of the video that I posted it clearly says Mercedes M272 timing chain tensioner. Mine was a visual one and yours was in printed form. Please tell me what the difference is.
 

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2011 E350 Bluetec
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41 Posts
When you plunge a tensioner while it is submerged in oil it should continue become more firm and hold the tension. Mine would leak oil at an unacceptable rate at the base (bolt side) of the tensioner. It was faulty. It is not supposed to work like that.

The tensioner in the video is a completely different kind of tensioner. It's a ratcheting tensioner whereas the one for the OM642 is simply hydraulic. I have attached pictures of the two tensioners for comparison.

Rather than deviate from this thread's subject matter please direct any further questions via IM.
 

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As a follow up:

The timing chain was replaced. 22 hours labor. Slap noise is gone. Better fuel economy and car clearly runs better (smoother/more power).

The mechanic stated that the chain was significantly stretched.
 

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2010 Ml 350 Bluetec
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8 Posts
The tensioner has a check valve at the rear and a pressure relief at the front, should not leak oil when squeezed by hand. The reason most of these get louder when you replace the tensioner is because the old tensioner gets broken due to over extension with the stretched chain. When you replace the tensioner the new one wont properly reach the guide so the chain slaps all the time. For those of you ignoring this and driving it good luck. As the chain stretches it will start to wear on the gears, balance shaft, guides ect and eventually cost way more to fix. If you are unlucky enough to have it skip a tooth or break your entire engine will be only worth its weight in scrap. It will make the 22 hours of labor to replace it look cheap. I really wish everyone who has this issue could pull together and push this back at benz. My wife and I test drove a 2013GL bluetec with 60K on it and the chain was slapping way worse than ours, they have a problem and I think most people just dont know.
 

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2010 Ml 350 Bluetec
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As a follow up:

The timing chain was replaced. 22 hours labor. Slap noise is gone. Better fuel economy and car clearly runs better (smoother/more power).

The mechanic stated that the chain was significantly stretched.

Do you know if they just did the chain or were guides and sprockets done as well? Did they pull the engine?
 
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