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I purchased a 2012 CLS 63 a few years ago with 65k miles. I just got around to changing the spark plugs at 107k (considerably overdue I realize) and scoped the cylinders. The car runs perfectly, no oil consumption and pulls like a freight train. No tunes and my spirited driving is limited to an occasional hard acceleration. Definitely no extended wide open throttle. I scoped each cylinder to see if I had the notorious scoring and was glad to see the walls looked perfect most of the way around the cylinder until I got to a specific spot in each. At first look this seems to be a terrible degradation of the cylinder wall but then I noticed debris collected on top of the piston that just looks like carbon breaking away from the spark plug during the removal process.
Opinions? Do I have a real cylinder wall issue or is this nothing? If this is really the cylinder wall coating breaking down in all cylinders I would think I would have misfires and need to add a quart every 1k miles.
Probably carbon,
Bores look great
( there has been a few pics posted that look almost identical to that bore pic of yours)
Run it…
Next time you bore scope it, the carbon deposits will probably be gone after some spirited driving and some 5k mi oil changes with SP grade oil. If you want to know engine condition, do a leak down test. Borescopes don’t test/see how valves or pistons are sealing. They also can distort what we see in the pictures of the bore.
Good Luck
(edit: see pics below from SEVERAL previous MBworld posters, notice deposits are near bottoms to mid cylinder)
Last edited by crconsulting; Jun 3, 2025 at 09:27 AM.
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