A puff of white smoke when gas is applied on a warm engine!

I did valve seals umbrella style last year on a 79 L48 and the blue smoke is gone, Put a 500 miles on it and all is good, this year, start up and shifting between gears is still good, no smoke but now after the car is warmed up I give it some gas like waiting at a stop light I get a big puff of white smoke out the exhausts pipes… no white smoke while driving just after it idling. No coolant loss, reservoir is clean, compression is 180psi, car doesn’t run hot, only on the interstate after 20 minutes, that’s another issue. Please help. Regards

I may be well off-base here, but...  About 30 years ago we had an issue and the car would put out a lot of white smoke, at various times.

That turned out to be the vacuum modulator on the (auto) transmission that had failed, allowing trans fluid up into the manifold via the vacuum line.   Replacement of the modulator cured the problem.

As I say, may not be the same as your issue....

I think that white smoke is also sometimes a sign of head gasket issues - not wanting to alarm you or anything!😀

4 speed or auto?

As already mentioned, white smoke is usually coolant.  😬

Check for white sludge in PCV valve or the bottom of oil fill cap. Another sign of water in system. 

4 speed, wouldn’t it blow white smoke all the time instead of just when equalizing gas/clutch after an 30 second (ish) idle? It’s only one puff of white smoke, then it goes away. 

Check both and we’re good, no blow by either. All this seem to start after I which to synthetic oil this spring, I just changed it again to high mileage regular oil and it’s not as bad but still blows white smoke only when equalizing gas / clutch after idling or a hard tap on the gas pedal after idling…

Thank you Kent, any information is helpful.

Did you install the new valve seals on both intake AND exhaust valves? Your description of the one time puff after idling sounds like a high vacuum situation pulling oil into one(or more) cylinders while idling. Could be excessive valve guide wear on one(or more) guides. Could also be a leaking intake gasket sucking oil into the intake port of a head, but that usually creates a more consistent smoking issue. 

Good morning Adam, I did both intake and exhaust valves put 500-1000 miles on it and no blue smoke on start up or driving or white smoke also last year, the car sat all winter. Drove it in the early spring, all was good, changed to synthetic oil from regular and that’s when it started??. Changed to high mileage regular oil and the white smoke is a little better. I’ll check the vacuum, that was on my list! Here’s a pic of the valve seals I used in 2024.

i would test coolant ,it gets really cold in wis ,go packers! . need more info to trouble shoot correctly ,did u just buy the car ,u said u replaced seals did u do it with heads on or off car the reason i ask is u also said on the hi way there is a temp issue? if coolant is weak it will cause engine to run hot combine that with real cold weather that could be a big problem,or could be water collecting in an old or incorrectly installed mufflers or exhaust system,whats up with the compression 180 psi did u ck all 8 that seems way too high for a stock L48 motor with 8.25 .is the motor stock or modified ?let me know ,mkie p