I joined the forum this morning to discuss my wifes Mini sporadically blowing puffs of white smoke from tailpipe. Leaning towards head gasket?? There are three basic colors of smoke from exhaust. Blue/Grey = oil issue such as bad rings. White/Gray = water issue such as head gasket. Black = fuel issue such as too rich.

What color is your smoke? Only when the A/C is on sounds little coincidental to me but sooo many things i don't know. Smelly?? if it's a white smoke and smells sweet like antifreeze then i would look towards head gasket.