So I recently picked up an old outback ll bean edition from an old friend. He claims that the head gasket went out and that's why it's over heating ( lucky for me because now he just wants me to get it out of his driveway)... I nursed it home and replaced the thermostat and did a coolant flush (and burped the system)...it kept it cool for about 2 days and then started to over heat again...problem is I don't see any white smoke coming out the back, milky oil (looks like a fresh oil change), discoloration in the coolent, or any leaking (driveway has no drips or signs of any coolent leaking)...not very familiar with Subarus and how they operate so any help would be greatly appreciated