Puff of white smoke on startup (after rebuilt heads, piston rings)

I recently had a set of rebuilt heads and the piston rings replaced on my wifes 93 mazda mpv minivan. The van only had 74k miles on it and was otherwise in good shape. After having the vehicle back for about week, I went ahead and changed the oil in the vehicle. The next week I have noticed a puff of whiteish (with a slight blueish tint) smoke comes out of the tail pipe right after starting the vehicle after it has been sitting for more than 15 -20 minutes. It seems to happen all the time after sitting overnight. The smoke only lasts about 3-4 seconds but it smells acrid, alot like gasoline. It's not the normal condensation that a car has after sitting for a while. The vehicle has not done this the first 300 or so miles, and has only recently shown up. Any ideas? I can't seem to put my finger on what the problem is. Also, the car seems alot harder to start since getting back. Is this because the rings were replaced and the piston to cylinder wall seal is a bit tighter?

Reply to
sb0494
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Reply to
pete selby

I guess the first thing to do is make sure that the rings are seating correctly. Any suggestions? I have been keeping the vehicle under 55 mph, under 3000rpm and made sure that I didn't keep the vehicle at the same speed for more than 5-10 minutes. Am I missing anything?

Reply to
sb0494

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I guess this only apply if the bores were honed when the rings were replaced.

Thomas

Reply to
Thomas Tornblom

You have a valve seal problem, most likely:

(1) one seal is torn, deformed or loose on it's guide

(2) the exaust and intake seals were mixed up (some manufacturers use different materials for each but they look almost identical)

(3) the wrong part number seals were used for your engine.

Any of these explanations could cause the slow increase in smoke on startup after an overhaul.

Also a valve could have been fit poorly into its guide and worn prematurely, causing a path for oil to leak into it's respective cylinder.

You will need to have your mechanic pull the spark plugs and see if one of them has more grayish soot on it than the others. Then he can just check/replace the seals used for that cylinder. Otherwise replace all seals and check valve guide clearances during the proceedure. This can be done with the heads on the car. Your bluish smoke on start-up can't realistically be caused by a piston ring or 'lower end' problem, so don't worry about that.

Reply to
ComboverFish

Everything you said up to here is a good possibility and a "most" likely suspect. The rings were messed with and experience says that makes it another good possibility especially since it is only a re-ring and an out of round hole will not seat the rings.

Reply to
pete selby

Except for the fact that a ring leak would not cause settling of oil in the combustion chamber after a sitting period. Unless the engine is installed upside down. My memory of the v-6 in MPVs is a little hazy, but I think they are installed rightside up and therefore not prone to the pitfalls you are predicting.

Reply to
ComboverFish

White smoke is usually from transmission fluid getting sucked into the engine. Don't know if that's even possible on your vehicle, it is on ones with vacuum modulators for the automatic transmission.

Blue smoke is usually from oil getting into the combustion chamber from leaking valve guides/seals.

You could also have white smoke (steam really) from coolant leaking thru a crack in the cylinder head or a bad head gasket.

Since it didn't do it for the first 300 miles, and assuming it's not related to the transmission, my first guess is either a cylinder head crack or leaking head gasket. Particularly if the hard starting coincided with the smoking.

Reply to
AZGuy

I've noticed lately that the smoke is whitish with definite blue tinge to it. I've taken it back into the shop (the work is warrantied for

12,000 miles, 1 year) to have him take a look at it. Thanks for all of your help, I'll go ahead and post a resolution, when I find out what it is.

Steveb

Reply to
sb0494

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