Same thing happened to me about a week ago. White smoke out the back. I need a new head gasket.
Water is leaking into the cylinders and causing it to get heated leading to steam. That steam is forced out the exhaust in what appears to be white smoke.
A lot of times this is caused when a car overheats. It damages the head gasket and sometimes the head is warped and needs to be refinished.
yippee!!! i diagnosed the problem, how much did it cost you?