Q: White smoke coming from underhood thermostat went up fast. Big leek under radiator on passenger side.

Hi there. when the white smoke appeared under the hood and there was a large puddle under the radiator, then the radiator hose may have blown off. This would be caused by excessive heat or excessive pressure. If the cooling system was weak and the coolant was boiling, then the system will build up pressure and blow off a radiator hose. If the head gasket was to be burned, then the compression gasses will make the cooling system to over pressurize and overheat causing the coolant to blow off the radiator hose. The radiator also could have been damaged. I recommend not driving the vehicle for it may damage the engine or transmission. I recommend seeking out a professional, such as one from Your Mechanic, to help you with your engine overheating.