what does white smke from the exhaust mean when car is started cold

The condensation and white smoke come from steam which is generated by water vapor in the exhaust. A car engine produces 1 gallon of water from every 10 gallons of gasoline it consumes. When the car is driven far enough to thoroughly heat up the exhaust system; the water boils off so quickly that it not noticeable; but when the engine is cool, or is used on a series of short trips, and the weather conditions are right, it is normal for the exhaust to put out condensation and white smoke as the car warms up. Every winter; people write in to ask about why their car is putting white smoke out the exhaust...There is, however, an engine problem which also puts water out the exhaust; this can happens when the head gasket begins to leak. The smoke from head gasket leaks does not subside as the engine becomes warm, it frequently smells strongly, and it often is produced in dramatically greater quantity than the smoke from normal condensation. The defining sign of a leaking head gasket is that the engine coolant level will drop rapidly in the radiator; and sometimes, but not always, drop in the reservoir. So it is necessary to remove the radiator cap (only when the motor is cool) to check the coolant level at that location; and not depend on viewing on the level in the reservoir. Since the radiator level will often drop gradually over months of normal use; if you find the level is low on one inspection, this does not confirm a head gasket problem. It is therefore necessary to fill the radiator to the top with a mixture of half coolant and half distilled water, and recheck the level several times over the next few days. It may go down again as air pockets work their way out of the system; but it should stabilize after two or three refillings. If it continues to drop after three fillings in a week; or drops faster as time passes; then there is an external coolant leak or a leaking head gasket.