My 2001 W203 C320 was belching out bluish smoke on startup after sitting off for a while, or after idling for a long time (like on a congested motorway). Other than that, no smoke during normal driving. It was also consuming a fair bit of oil. Definitely not head gasket.

Took it to an indy and he said it was valve stem seals, he ruled out piston rings since the smoking didn't happen all the time and even taking it to 4000rpm up a hill didn't necessarily produce it. He also replaced valve cover gaskets and spark plugs at the same time. PCV system was ok.

I took the car back and went for a 40 minute city drive, to my horror I saw smoke billowing behind me when I took off after spending ages idling in a congested motorway, cleared up after a few seconds. I went home and left it sitting in the garage for a few hours and started it again, I could see copious amounts of smoke coming from the exhaust, just like the original problem. My country's got a 3 day public holiday and I won't be able to contact any mechanic till monday. I'm at a loss to understand, if it isn't rings or seals, how else can oil get burnt? I did a bit of googling and it could be valve guides but shouldn't they have found that if they were replacing the stem seals?

I should also mention that the engine is suffering from quite a bit of sludge, could this be causing excessive oil to pool on top of the valves for ages and cause the leaking? I read somewhere that if the oil is impeded enough, then no valve seals will keep the oil out.

Oil treatment? I wouldn't be surprised if your rings are coked up.

If you've got heavy sludge the oil returns are blocked. Oil builds up under the valve cover and gets sucked past the valve stem seals. Smoke and rough running are the symptoms. Not uncommon to the M112. IMHO, your guy should have seen this when he was in there. It's pretty obvious......

He definitely saw it, he even took pictures, though he didn't say anything about it causing problems with the oil leaking. Would this be what you're talking about?



I can't think of anything else, either this or they installed the seals incorrectly. Still don't think it's rings since a coked up oil control ring sounds like it would smoke constantly. He did say it would require an engine oil flush at the next service in 3500km but judging from the smoking I'm inclined to do it ASAP. He cleaned as much gunk off as he could by hand off the valve cover and what's visible in the picture, though it's probably still blocked up somewhere down the line. I'll contact him as soon as he gets back and see what he says.

My vote would have been valve seals as the symptoms are classic. I replaced valve seals on countless Chrysler mini vans with the Mitsu 3.0. It is possible to damage the seals during install, either by carelessly jamming the seal over the stem or using a too small driver that damages the seal top. I'd look for other sources of oil first though.

This engine might have a problem with the venting baffles in the valve cover clogging up. There might have been a post on this site with a fix.

In any event, please post the results so others can benefit.

I agree one or more seals may have been damaged upon installation. I've done that myself. One little tear in the seal and you'll get oil down in the combustion chamber. Or one may have slipped off its seat. Time to pull the valve covers and springs and have a look.