It may depend on what country you live in, as if the weather is cold it probable is just condensation ( water vapour ) In New Zealand cars do this in the winter, it is no different than your electric jug. As every gallon of petrol you burn their is about 4 gallons of water that come out the exhaust. We learnt this training to be a motor mechanic. Water vapour is white and oil burning is grey or more like smoke they are different. Once the motor is warm it will stop, if it is vapour , but if it is oil it does stop it does it at any time. Hope this helps, without talking to you.