Exhaust smoke after 5 minutes?

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Paul Barrett - 13 Aug 2006 04:39 GMT

I'm fixing up a '76 Chevy Malibu with a 350. Until a month ago, it had sat
undriven for about 3 years. Before that, it would smoke a little at startup
then would be fine. I figured it was valve seals.
Recently I've unclogged the PCV valve, replaced/reconnected vacuum lines,
put in a new battery, and changed the oil which was black and seemed very
thin. I also changed the plugs, which were all oil-fouled.
Now that it will start again, a few things have changed. It now doesn't
smoke at startup, and idles smoothly, unless I put it in gear, then it
generally dies until I get it warmed up, then it'll keep running in gear.
After about 5 minutes, then it gradually starts belching blue/grey smoke
from the exhaust.
My guess is that somehow over the 3 years it sat, oil got into the
exhaust/muffler and doesn't start smoking till all that gets hot. Does that
sound possible? If it was just valve seals I'd expect smoke only at first,
and if it was piston rings, I'd expect smoke all the time.
I'm guessing that if I ran it long enough it'd all burn off. But after a
few minutes it really clouds up the neighborhood.

Any thoughts/suggestions?

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Don - 13 Aug 2006 06:27 GMT

>I'm fixing up a '76 Chevy Malibu with a 350. Until a month ago, it had sat
>undriven for about 3 years. Before that, it would smoke a little at startup
[quoted text clipped - 15 lines]
>
>Any thoughts/suggestions?

Leaking vacuum modulator on the automatic transmission. It's drinking
transmission fluid. Check transmission fluid level, check for the
presence transmission fluid in the vacuum line from the modulator to
the intake manifold. Easy to fix.

Don
www.donsautomotive.com

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sdlomi2 - 14 Aug 2006 15:28 GMT

> I'm fixing up a '76 Chevy Malibu with a 350. Until a month ago, it had
> sat undriven for about 3 years. Before that, it would smoke a little at
[quoted text clipped - 15 lines]
>
> Any thoughts/suggestions?

Don could be right--esp. if the smoke is whitish. Also sounds just like
oil return holes are partly stopped up, allowing tops of heads to puddle
with oil as it runs, until the level is above the valve-bosses(where seals
do their thing). Until the level reaches this height, the seals function
fine; however they are not designed to work "submerged". Remove valve
covers, clean out return holes (old speedometer chain works well, as it
flexes and goes around corners and moves solids; also air compressor helps
by blowing air down thru holes), and your problem should be solved.
Should you wish to know for sure, remove all v-cover bolts except one,
remove all else needed to remove THAT v-cover, let it idle until smoke
begins, then cut off and instantly remove the last bolt and cover. You
should see the puddle, if this the problem. The oil may even pour out over
the heads. **Try looking under the side that DOES NOT have the pcv valve
either in it or a hose directly from the pcv valve leading to it--the
'without-one' side usually puddles first.**
Enjoy your now smoke-free Malibu, but your neighbors will hate you for
allowing the mosquitoes to return!!! s

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