My 2006 Subaru Outback overheated when my wife was driving. I got to the car that evening and its radiator was pretty low. I refilled it, and the car ran fine for a week. Then it overheated again. Our mechanic says we have a blown head gasket. We need to wait before we can pay for that repair, so we took it home for now.
I drove it today. It ran fine for a few hours, then rapidly started getting hot. I opened the cap and let it boil, filled the radiator (it took about a half gallon), and kept driving. It overheated again in about five minutes.
This happened about four times over 15 miles - It would suddenly get hot after approximately five minutes of easy driving; I would open the radiator and let it boil off; refilled it with water; and kept driving towards home. It had just started getting hot again when I got home and parked.
Anyway, here's what is confusing me. After it cooled off, I opened the cap (without it needing to boil off), and the radiator was still full! Perhaps most of the coolant I lost on the way home was simply due to my opening the hot radiator and letting it boil... It does lose a bit of coolant even when it isn't overheating, but that might be a hose leak.
Can this behavior be explained by a bad head gasket? The system can obviously hold pressure. I'm wondering if the thermostat is bad instead. Maybe both problems exist.
Thanks for any insight.