Got a 98 buick lesabre for my daughter. It has about 90k. She put about 5k on it. She told me it was running rough. I drove it and it ran fine. It got hot though. I came home and the radiator and reservoir were empty. I put about 1.5 - 2 gallons of coolant into the radiator and reservoir. I started the car and it ran rough for about ten seconds, blowing white smoke from exhaust, then it died. I checked under the hood and all the coolant was gone. the coolant is in the oil pan. Is the engine done?