Ignorant mechanical question #712: Yesterday my car was idling in the 98-degree heat for a few minutes while I checked and filled my A/C freon. I noticed random puffs of bluish smoke emerging from my tailpipes every now and then. Not a major blanked of smoke, but enough to see from the front of the car. What could cause this? Major or minor problem? The car is still running fine - does it matter or should I just keep driving it and not worry about it? I had not driven the car for a couple weeks because it's been so hot and the A/C was not working properly. (Dark gray seats, no A/C, and a 2-year-old don't mix when it's 100 degrees out!) So I don't know if it was only doing it that once or if it's been this way for a while because there would have been no way for me to see the smoke if I'd been driving it down the road. I have a 1978 350 SBC with about 75,000 miles on it in my '53 Chevy. Internally the engine is totally original. The only changes I made were to replace the intake manifold and carb with an Edelbrock Performer and 650 cfm carb and replaced the manifolds with ram's horns. I've been driving it this way for about 10 years, putting maybe 1-2,000 miles on the car each year. (I only live 15 miles from work, so driving it several days a week most weeks of the year just doesn't add up to much.) Just this past year I replaced the original vacuum advance canister with an adjustable one because the car had been pinging and I didn't realize it until I swapped to quieter mufflers last summer. It has been giving a nice little puff of blue when I start it up for quite some time; damn valve stem seals that I did not replace while the engine was laying on my garage floor. But the car does not burn oil - after 2,000 miles it's typically at or near full.