Hi everyone. My wife's 1994 Excel occasionally blows out some blue/black smoke when it's started from cold. It does not smoke apart from that and does not do it every time. I don't think it is worn rings as it is intermittent. It seems to run ok ...any ideas?

This post has been edited by Eddo: Jan 20 2005, 11:07 PM

Hi Eddo

When was your last tune up and oil change? Dirty spark plugs cause inefficient combustion. Old oil tends to leave residue on cylinder walls which, incidentally, fouls spark plugs in a hurry.

These are the first things I'd look at. If you are a bit behind on maintenance I'd suggest new plugs, an engine flush and oil change. There are also fuel additives that will clean off build-up in the compression chambers. Go for a high quality plug like NGK rather than Champions.

It could be a bad oil seal on a valve stem. When you shut the engine off the oil in the top of the engine will normally run down into the crank case - a bad valve seal lets oil seep into the compression chamber instead and then burn off when the engine is started.

If you pull the spark plugs and one seems more fouled than another than a bad valve seal is very likley the problem.

This is not a huge deal for an older vehicle - it will just get progressively worse over time to the point where your neighbours will not like having a cloud of blue smoke blowing their way in the mornings.

I have this with my old Civic, which is now of legal drinking age in most places.

It could also be a ring problem if the rings are worn in such a way as not to provide a good seal when the engine is cold. As the engine warms the rings expand to better fill the gap between the pistons and the cylindar walls.

Worn rings will show up in a compression test. A normal part of the test is to test compression then spray oil into each cylinder. If the compression improves your rings are worn.

Your engine could be burning oil without showing a lot of visible smoke. Once the engine warms the oil is more liklely to burn completely and not show as much.

Have a look at the exhaust pipe - is the inside grey or black - it should normally be grey. It is is black like soot then you are definitley burning oil.

Gordo, thanks for that. The car has recently been serviced and runs pretty well (new plugs, an engine flush and oil change were all done). Rings and/or valve seals had crossed my mind but you would normally expect smoke all the time rather than the odd puff occasionally. It is only when starting the car too - there is never any smoke when it's running, so the neighbours haven't got anything to complain about yet...! Perhaps it is the valve seals just beginning to go.

oil smoke on startup generally indicates valve stem seals. this can easily be done without removing the head, and I would do this first.

Duke - thanks, will do when it gets worse!!

don't wait too long, the excess oil in the combustion can screw your cathalitic converter (if you Ausis have one).

Very good point, Duke.

By the way. Do you have any experience with or thoughts about "high mileage oil"? - its supposed to revive old seals.

I'm actually an Englishman living in Australia, but yes, catalytic converters have been here for some time and your point makes sense. However I have noticed that there are many more 'heavy smoking' cars and trucks over here than in England. In England all vehicles have to go through an yearly mechanical / safety test and a smoking exhaust would automatically fail. No such test in Western Australia....presumably the cats on those cars are all screwed as you put it!

maybe the smog test will come to "down-under" eventually.

gordo,
I use (and highly recommend) Castrol Syntec 5W50 (for all year round use) in all my cars for years. My old 1990 Sonata 2.4 had 436K km when I scrapped it (too much under-body rust due to heavy winter road salt), without any engine repair. The engine used +-1ltr oil in 5K km when it was scrapped.