Why is your car smoking white smoke out the muffler?

As a grand master service technician I would have to say, given the question at face value, white smoke = coolant burning in combustion chamber. White smoke with blue tinge=oil burning in combustion chamber. Car running really bad with white smoke. defective ignition system(dead cylinder). Either way you will notice minor/major fluid loss from engine oil or coolant.

Since we always seem as mechanics to give the worst case scenario, the most probable and most common cause is steam from the combustion process from burning fuel. More common in the morning or on humid and cool days. If you can produce steam from your breath, chances are your vehicle will do the same thing. Which of coarse, is a normal operating characteristic of today's modern vehicles.