Bad Engine Noise <Video> Need Help! - Mercedes-Benz Forum
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post #1 of 5 (permalink) Old 08-28-2014, 12:18 PM Thread Starter
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Unhappy Bad Engine Noise <Video> Need Help!

This is a M112 V6 2.6L engine on a C240 but am posting here since this is the same exact engine more commonly found on the E320. Except the smaller cylinders.

It only has about 105k miles. I have had multiple of these cars and they run great even at much higher mileage.

This one has developed a noise, which sounds like a timing chain noise to me. But I am not sure.

I have checked the oil pressure and that is within range.

Removed the serpentine belt and the noise is still there.

What do you think?

Please listen to the video. You can here the noise I am talking about even before I open the hood.
https://www.youtube.com/watch?v=1Hlqs4-0cwg




Thank you in advance.
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post #2 of 5 (permalink) Old 08-28-2014, 01:06 PM
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It's always difficult to tell on a video, but in the beginning the noise is quite loud indeed. However, it seems that after 30 sec. or so it got much quieter--is this impression correct? Which begs the question: was this a cold start? Or had the engine been running before?

It's difficult for me to tell if the noise is rather of a chattering or of a chafing/clattering nature. The first would be more typical for the valve train/lifters, the latter for the chain. If this is indeed after a cold start, then it is conceivable that either the lifters are not lubricated well in the first moments or that the chain tensioner takes some time to build up pressure and tension the chain properly. Both these scenarios would explain why the noise disappears after a while, if, indeed, it does.

Also, which oil are you using? Have you recently changed it? Is there evidence of sludge in the engine? Especially the smaller, 2.6l M112 engines are reported to have a certain propensity for sludge build up, especially so at the top end. Have you ever taken the valve covers off? Unfortunately, on this engine you can't see much when you look into the oil filler tube.

But if I were you, I would first of all spend a few dollars on a "mechanic's stethoscope" and listen carefully to different parts of the engine (top end, front cover, with belt off). Chances are that this way you would get a much better idea of where the noise originates.
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post #3 of 5 (permalink) Old 08-28-2014, 01:45 PM
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If the noise does indeed go away after the engine has been running for a bit, then it may be a bad pressure relief valve (oil non-return valve) above the oil pump. There is a tech bulletin around someplace that I cannot locate, but I recall reading about it, probably on this forum, maybe at peach parts. The part has been superseded several times, so that's another indication of known issues.

If the noise never goes away, then I'd be getting the mechanic's steth as well. About $4 over at Harbor Freight if you have one in your neck of the woods.




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post #4 of 5 (permalink) Old 09-01-2014, 05:09 PM Thread Starter
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Thank you guys for the replies. I do have a stethoscope and have tried to listen with it. But it seems like I hear noises all over the engine. A bit more noticeable on the front.


Never hear of the oil releaf valve.


Like I said there is plenty of oil pressure, but the wired thing is that:
When I look at the engine oil level on the cluster (this is a w203 tells the exact location of oil), the oil level doesn't lower more than 0.5L from the car off to car started. Even if I rev up the engine I don't see more than about 0.5L oil decrease from the pan.

Which is making me wonder if there is restriction past the oil pump. Yes it has a new fleece filter.
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post #5 of 5 (permalink) Old 09-01-2014, 05:12 PM Thread Starter
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Quote:
Originally Posted by Simon_E View Post
It's always difficult to tell on a video, but in the beginning the noise is quite loud indeed. However, it seems that after 30 sec. or so it got much quieter--is this impression correct? Which begs the question: was this a cold start? Or had the engine been running before?

Yes, this was a cold start. It does get quitter, but it's still very loud. Sounds like a diesel VW, maybe even worse.

Changed oil a couple of times.

At the time of video was running thin oil plus 2 L of risoline.

Tried thicker with lucas that didn't help. Made it worse.


Have not taken the valve cover off to see.
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