Smoke (not white) from the exhaust. Help needed.

"duurtlang" (duurtlang) 08/03/2016 at 18:08 • Filed to: peugeot 205 cti

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My 1987 Peugeot 205 CTi is a project car that hadn’t run in many years. It runs now, but it smokes. There’s oil on the plugs, on the inside. My mechanic says: probably piston rings, better swap the engine block. What says you?

We’ve already replaced the valve stem seals, which were a likely cause. However, they were not and it still smokes. In a compression test one of the cylinders has 10% lower compression than the others.

I’ve read stories about throwing certain fluids in the oil or directly in the cylinders to loosen the piston rings. Worth a shot?

Besides smoke there’s also a sound coming from the engine when accelerating that sounds like a bad bearing. It seems to be getting worse, but that might also be psychological because we fixed the exhaust, which made the car more quiet.

For those that don’t know: it’s a fuel injected engine without cat.

On the day I bought it, last year.

KatzManDu > duurtlang 08/03/2016 at 18:21

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It’s late and we should be asleep, but typically black smoke means oil in the cylinders, and if one cylinder is 10% lower it could be the culprit. The trick would be that one cylinder would have an oily plug while the others wouldn’t. It would almost be smart to replace the plugs, drive it for a few days and then check plugs again.... and again and again and see what the differences are.

You may also have a case of “need to drive the piss out of the car” — some vehicles have piston rings that fit more loosely and are intended to get warm and expand with usage. When the engine isn’t really warmed up, the rings don’t expand and oil blows by. The early E39 M5s are notorious for this and “eating oil” because people weren’t driving the crap out of the cars, they were just making small commutes with their fancy cars and they were going through oil like crazy. If they were driving for longer trips or more “spirited” driving they wouldn’t eat as much oil.

duurtlang > KatzManDu 08/03/2016 at 18:27

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Well, this car sat for 9 or so years until last year, when I bought it. I then drove it for 2 hours at highway speeds, and didn’t run it after that for a further half a year. I then changed the oil. I needed to hammer a screwdriver through the oilfilter (which looked ancient) to be able to remove that filter.

So you’re saying that, after it’s warm, rev the nuts out of it for a longer period of time on a spirited drive and it might get better?

I’m still up because jetlag. That, at least, is my excuse.

If only EssExTee could be so grossly incandescent > duurtlang 08/03/2016 at 18:56

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As long as the cylinders aren’t scored I don’t see why bad piston rings would necessitate a new block.

RallyWrench > duurtlang 08/03/2016 at 19:18

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Burning oil creates bluish smoke, not black. Black usually indicates excessively rich running. Oiling the plugs could be bad rings, but does it do it more on any one cylinder? Are we sure it’s oil and not fuel fouling the plugs? What’s the compression across all 4? Low compression causes incomplete combustion, which can give the impression of rich running. Was the valve stem seal repair done properly? If the stem seals are bad, the engine will tend to smoke on overrun as vacuum in the cylinders pulls oil past the valve seals, but smoke under acceleration and at idle can mean rings. Any chance you have a video of that noise?

Sorry for all the questions, but, well...

Jonee > duurtlang 08/03/2016 at 19:39

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Beautiful car. I feel like this should be able to be solved without needing a new block.

duurtlang > Jonee 08/03/2016 at 19:53

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It can be, but according to my mechanic installing a new block would be cheaper. Still though, if the piston rings are merely stuck they might be able to come unstuck?

LOREM IPSUM > duurtlang 08/03/2016 at 20:04

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Maybe a stuck pcv or blocked crankcase vent if so equipped?

Fwiw, blue smoke is usually oil burning. Black smoke is usually indicative of a overly rich condition.

duurtlang > RallyWrench 08/03/2016 at 20:11

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It smells like burnt oil. Blue, black, probably blue. Anyway, not headgasket-white. I’ve seen it spout a few drops of oil out of the exhaust at a cold start after not having run for months.

All plugs had oil on them, I at least believe it was oil. It was black. The car sat for about 9 years before I bought it if I’m not mistaken, I don’t know what color gasoline gets after that long. Due to the previous owner the car was then run for multiple hours on that old oil before I got the chance to change it.

I can’t tell you the actual readings of the compression as I don’t have them on me. All I know is that one cylinder was 10% lower than the other 3.

The car is at my mechanic (a brother of a friend) currently. It’s my project car, but there were a few things I’d rather not do my inexperienced self (like the timing belt). He did the valve stem seals in the last few days. I can’t tell you if it was done right, but I trust him. The smoking was there before he did it, and it’s still there. Sorry, no video. I could ask him though.

For arguments sake, let’s assume it’s the rings. My friendly mechanic tells me changing the block would be cheaper than changing the seals + treating the block (regrooving? I lack the English vocabulary). After a google search lots of forums have told me stuck rings in an engine that’s sat for many years isn’t uncommon. Forums are never wrong. Rather than getting a new block or new seals getting the old seals to work would be best, if such a thing is possible. Sadly, I read a different solution on every website, although most put some kind of cleaning liquid through the plug holes to remove carbon/gummy stuff/rust/whatever that’s affecting the rings. I wish there was some kind of reliable mechanic-wikipedia for such a thing, especially for someone as inexperienced as me.

RallyWrench > duurtlang 08/03/2016 at 20:39

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I see Kinja ate my Johnny Five Need Input meme in the last post.

Lots to process there. The 10% compression difference doesn’t really worry me at this point, but if they’re all lower than expected that would be telling.

It is common for rings to stick in engines that have been sitting, but as you mentioned, they can potentially be freed up. You can use ATF as a detergent to clean them, either added to the engine oil and running the engine, or pour some directly in the cylinders and let it sit for a bit, and there are other products that work well. Here in the states I’ve used a product called Rislone that has drastically reduced the smoke on a couple of old engines (a Mercedes 220 and 2.4L 911) that had sat. I don’t usually believe in stuff like that, but I saw it work.

If they don’t improve, it’ll need to come apart but not necessarily to replace the block. It may be that it’ll just need rings and a hone (that’s a simple refinishing of the cylinder bores, no actual boring to oversize. The cylinders and pistons will need to be measured to determine if that’s feasible. Of course, I don’t know what a known good used engine goes for over there, that may be more economical if it comes to that.

For reference, this is a hone:

It gets attached to a power drill and run through the cylinders thoroughly to more or less duplicate the cross hatch pattern it had originally. It used to be much more prevalent, the kind of thing the corner garage could do, but now it’s kind of seen as a half-ass thing. Definitely not something I’d do for a proper rebuild, but given this car’s story it might work if things measure up ok.

Jonee > duurtlang 08/03/2016 at 22:45

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Yeah, if they’re stuck from sitting, they can free up with use. It might only be one or two that are a problem.

El Darto > duurtlang 08/04/2016 at 04:03

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First thing I would do at this point is put some Marvel Mystery Oil in the cylinders and let it sit for a few days.