Could be carbon deposits from the motor. Might not have been flogged by the previous owner and due to this the deposits build up. Generally a new owner will wanna see how it goes. So getting up it may be getting rid of the deposits and give you the white powdery smoke Have you ever been behind a car when you see like a grey white powdery puff comes out the exhaust, when they're accelerating hard. This is the carbon deposits being blown off Just keep an eye on your fluid levels. Should be fine