91 GMC Sierra smokes at startup


Old 07-06-15, 12:19 PM
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Join Date: Apr 2011
Location: USA
Posts: 159
91 GMC Sierra smokes at startup

My 91 GMC Sierra smokes at startup and when pulling away from traffic lights/stop signs. I'm sure it smokes all the time, but is most noticeable then. I've had the truck for 4 years and only put 5000 miles on it. It has smoked since I bought it. I'm going to start using it more often now and would like to stop polluting the air. It's obviously an old truck, and has nearly 200,000 miles on it. Family/friends keep telling me it's not worth fixing. I'm going to do the work myself, so it's just a matter of time and a few gaskets I'm guessing. Assuming the problem can't be easily narrowed down to just one fix, where should I start? What would be the most likely culprit? I can start with one fix and move to the next until there's no more smoke.
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Old 07-06-15, 12:43 PM
Join Date: Jan 2013
Location: U.S.A.
Posts: 1,378
My first guess would be valve stem seals, but it's been a long time since I recall changing them, certainly nothing that new, so can't give you much direction beyond that, except to suggest researching it a bit, and I think you will find it worth considering.
Old 07-06-15, 01:28 PM
Join Date: Jan 2010
Location: North East Kingdom of Vermont
Posts: 2,278
Is it a V8 ?

I'd get a compression test and check the rings, which may burn oil at lower temperatures; but ceases (now) once the engine warms up, and the rings expand.

It would be a shame to tear the engine apart just the replace the rings; but if that's all that's needed . . . . that's what you do.

How many miles on that rig ? . . . . Never mind, I now see 200,000. Are you changing the oil at least once a year ?

Last edited by Vermont; 07-06-15 at 01:52 PM.
Old 07-06-15, 09:05 PM
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Join Date: Apr 2011
Location: USA
Posts: 159
Thanks for both replies.

It's a 6 cylinder. I suppose I should change the oil every year regardless of the mileage, but I have instead been changing at about 2000 miles.

It's an old truck for sure, but I love it. I enjoy tinkering with the small issues that come up. If this was my only ride, I might not like that so much though . I would like to get rid of the smoke. As I was pulling away from a light this evening, looking back in the mirror, I could see a cloud of smoke. It's not blinding by any means, but I'm sure people behind me have had a few choice words at times.
Old 07-07-15, 04:24 AM
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I also would bet on the rings being bad.

I'm just saying that if you're going to tear it down to put rings in it, I'd do the rod bearings while I have the pistons out.
If you've got much wear in the cylinder walls, you might need to hone out the cylinder walls then have it mic'd & go with over size pistons. That can add more to your cost, by buying new pistons etc, but if you dont, you'll still have oil getting past the rings... & the smoke.

Good luck. Hope this helps.....

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