The most common cause of white smoke from under the hood of a vehicle is an overheated engine. In this case, the driver is actually seeing steam from the radiator instead of smoke. However, if a burning smell accompanies the smoke, there is likely another type of fluid leak.
When there is smoke or steam emitting from the hood of a car, the driver should maneuver the vehicle off the road to a safe spot as quickly as possible to determine the cause. If the driver suspects overheating, turning off the air conditioning and turning on the heater helps cool the engine. Stopping the smoke or steam requires determining where the vehicle is leaking and making the appropriate repair.