My boyfriend 99 mazda 626 is overheating and also has no heat. He had a coolant leak and had it fixed and flushed. But was still overheating. Found another leak today, and got that fixed. I put in a new thermostat, hoping that fixed it but didn't. Coolant still seems to be leaking somewhere, but doesn't seem like a big leak. So I still have to find that. I had a friend look at the car, he said there is white smoke coming out of the exhaust and could be blown head gasket. I'm really hoping it's not, cause I really don't feel like changing it, but also don't have money to pay someone to do it. Could it be anything else besides blown head gasket? Like maybe heater coil, or sensor? Or if it is the head gasket, does any of the sealers work? Or should I go ahead and change it.