I have a 1990 honda accord with 348,000km. recently it began to take longer to heat up the interior, and yesterday, the car overheated, but it would not heat up inside the car. I checked the fluid and the rad was dry, so I filled it totally up, drove around for about 20km, and the same thing happened. the rad was dry again, and the car was running weird. I'm hoping its the thermostat. Would a bad thermostat cause this problem, or am I looking at a head gasket replacement? I could neither see nor smell radiator fluid leaking from under the hood. Anyone with knowledge have any ideas?