M112 rattle?

[rich1068]

You may or may not know that I have a 2003 W209 CLK 240 with the 2.6 M112. I've owned it since May last year, two owner car and I picked it up with 79k miles and I've since put 6k miles on it. It's had 3 oil changes since I bought it (one on purchase, one after 6 months, one after 12 months) and each time I've used the correct MB 5W40 oil and MB filter. Previous owner had it since 2006 and service history is a little patchy but he hardly did any miles though there is evidence of regular-ish servicing. The last couple of years it barely moved until I bought it.

Now, the issue. It's noisy. It wasn't when I first got it but it is now and I'm not sure if it's chain rattle, sticky tappets/lifters or what. I can remove the drive belt to eliminate noises from the front and the rattle remains. Using a long screwdriver to my ear the noise seems internal. I've read over and over that the M112/3 is bombproof but that it's not uncommon for this rattle to occur and the engine to perform exactly as it should for many thousands of miles. I've also read that if things got more serious and for example the chain were to be stretched I'd get plenty of warnings via dash lights and codes of which there are none.

So, any thoughts?

Short video of the noise.

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[rich1068]

Does anyone have any suggestions? I know the video isn't the best but if you turn up the volume you'll hear the rhythmic rattle the engine now makes.

Btw, tried a bottle of Liqui Moly Hydraulic Lifter Additive last week but that's made no difference to the noise.

 

[slade1]

STP does stop chain rattle, have used it.

 

[rich1068]

STP does stop chain rattle, have used it.

I'll look into that

 

[rich1068]

I'd have to wait until I do another oil change before considering another additive so does anyone else have any input regarding the noise?

 

[slade1]

Don't mix additive, may use different chemicals and make the problem worse.
Also check chain tensioner is working properly.

 

[rich1068]

I'm just chasing my tail with this so I've booked in for an hour of investigation at Europa Mercedes in Sheffield. There are guys there who have worked on these engines since forever so hopefully they'll have some answers.

 

[jo2020]

Might be too late for you....but use stethoscope or short length of hosepipe in one ear to locate the source of the noise...sounds like pulley / bearing from the video....