During my Thanksgiving break, my Dad started up his car and was unpleasantly suprised to find that it was belching foul smelling white colored exhaust. When running properly, a car should not produce any colored smoke out of its tailpipe at all (unless the car is a Diesel, or it is cold outside). I remember going to the auto auction for my old job and passing on buying cars that otherwise looked fine but were producing small amounts of white colored exhaust from the tailpipe. This white smoke could stem from alot of things, and unfortunately none of them are good. The most likely cause is that the engine is burning antifreeze or engine coolant along with the fuel. This means that the car has a blown head gasket or seals, and this is an expensive fix. Black smoke usually denotes that the car is burning oil along with gasoline. Blue smoke also means that the engine is burning transmission fluid. These are all very expensive fixes as well, and unfortunately replacing the wrong parts by yourself can lead to more engine wear and more damage to the car. If this happens, the problem should be looked at by a certified mechanic to correctly diagnose what’s wrong. And if you happen to be looking at a used car, I would just pass on the vehicle unless it is an extremely good deal or you are good friends with a mechanic!
I have seen both cases on cars, and they are usually death sentences. Either extreme wear is causing oil burning, or cracked blocks or blown head gaskets cause them to burn coolant. In many cases, they cost more to repair than the value of the car.