Don't be so fast on that drewkaree. Seafoam can indeed cause some 'minor' smoke from the gas tank. It is flowing through your engine/combustion cycle and exhaust. Not every car will smoke from it, alot of variables... but yes, absolutely, it *CAN* cause some smoke.
It will not, however, cause the massive smoke you get from putting it through your vacuum line.
I can personally attest to smoke from Seafoam in the gas tank, especially as your fuel levels get lower and the seafoam becomes more concentrated.
It will stop (if it happens at all) after you go through a tank of gas and fill up again. (At the very longest).
If your engine continues to smoke well after the above, it isn't the seafoam as drewkaree is indicating, you would then need to judge by color of smoke, intensity (on startup.. all the time?) -- and smell.
Check fluids, and then monitor/mark their levels and continue to check. You will find your culprit soon enough.
Check, oil level, coolant level, PS level. One of those 3 will be the only fluids causing constant smoke beyond what sea-foam could do. And one of them WILL go down at some rate.
If it is just a minor , minor smoke that isn't dark in color, and is only at startup and goes away -- It is usually normal, no fluid leak. Our exhaust (in good condition) -- Cats.. create H20 , which will sit in the pipes, and when heated steam out. Same principle as the engine running on a cold'ish day.
Haulin, now I know you are probably confused with two different answers -- But I'm sure others will chime in and agree with what I've said. If you have not experienced smoke from sea-foam just say that, but don't indicate that because you didn't see it, or it didn't happen in your vehicle that it isn't possible
Btw.. smoking or not, sea-foam in the gas isn't going to hurt anything, so if you are worried about safety, don't be.
Just don't pour 3 cans in there , or anything crazy like that.