S280 (2005) Undiagnosed smoking issue

[LostKiwi]

The M112 engine is about as tough as they get. I would be surprised if this requires a new engine to be honest.
The usual problem with the M112 is crank position sensor failure or crankshaft pulley delamination - both relatively cheap fixes.
I've had issues with the past on a pair of C240s I had and both times once sorted they ran perfectly for many more miles. The issue seen was very high oil consumption and smoke so fingers crossed yours is the same.

 

[Alanfrank]

The M112 engine is about as tough as they get. I would be surprised if this requires a new engine to be honest.
The usual problem with the M112 is crank position sensor failure or crankshaft pulley delamination - both relatively cheap fixes.
I've had issues with the past on a pair of C240s I had and both times once sorted they ran perfectly for many more miles. The issue seen was very high oil consumption and smoke so fingers crossed yours is the same.

That is encouraging to hear. Everything does seem to be pointing towards a breather problem. A mechanically astute mate of mine has suggested removing the dipstick and driving without it in order to introduce some air into the system as some sort of test. To be fair, it is still running rough and there is the odd puff of smoke but it definitely runs better without the dipstick present so breathing issues do seem to be the favourite but obviously I am open to any other suggestion.
Thank you
Alan

 

[Uncle Benz]

Another common smoking issue on the m112 is caused by a blockage in a narrow oil drain back passage concealed by a plate behind the flywheel. The narrow passageway is almost like a U bend. If it blocks with debris the offside cam cover fills up with oil that cannot escape, pushing it out through the breathers.

I'll try to find a picture. I have one somewhere...

 

[LostKiwi]

If it's drinking that much oil the plugs may well be contaminated. It would well be worth checking them.

 

[Uncle Benz]

Hurrah!

 

[Uncle Benz]

I've seen this a few times, exclusively with cars that have missed regular oil changes.

 

[LostKiwi]

I've seen this a few times, exclusively with cars that have missed regular oil changes.

Yep that's what seems to do it with the cam covers too though one of my M112s was new and always serviced on time by MB and still did it.

 

[Alanfrank]

If it's drinking that much oil the plugs may well be contaminated. It would well be worth checking them.

You’re correct. When the garage did the compression test they noticed that all plugs were covered in carbonated oil. All plugs and leads were changed but the problem has persisted. I intend havingbthe breathing system either overhauled or replaced as soon as I can. I starting to have my doubts about the garage I have been using as they were quite dismissive of the suggestion that it might be a breathing issue, insisting it was a serious engine fault which would only be identified by stripping the engine down. You and all other posters seem convinced the problem lies in the breathing system as did the MB main dealer parts depot. My money is in you lot (literally)
Thanks again I’ll make sure to report any update. Cheers.