Join Date: Dec 2011
Location: Dayton, Ohio
Car Year: 2012
Car Model: XT Touring
Feedback Score: 1 reviews
I can't solve your problem, but here are a few things to consider. Your cooling system has more than enough capacity to cool the engine - even in Florida, and even if the system is not pressurized (that is, you have a small radiator seam leak). So, if you are experiencing overheating and there is no other obvious issue, it's likely to be a head gasket. Even a small injection of combustion gasses into the cooling system will cause overheating. A leaking radiator (resulting in no or low pressure) will probably not cause overheating.
As for the thermostat, if it is stuck open, you would expect the engine to warm up more slowly. But, other than that, it really should not matter. If working properly, the thermostat opens rather quickly, and 'open' is 'open'.
If the thermostat is stuck closed, it could cause overheating. But there should be a by-pass hole in the thermostat frame, so some coolant will still circulate.
Finally, the cooling system should be 'closed' system - nothing entering or leaving. So, if you fill the radiator and overflow (and mark the overflow level), the overflow level should rise with the engine is hot, and return to it's original level when the engine cools down. If the level in the overflow starts going down over time, you have leak . . . period. Find that leak.
Again, it could be a head gasket, but it could also be a leaking radiator. Subaru plastic radiators of your vintage have a finite life. At 140k, you're on borrowed time. The leaks can be hard to find, but if you're driving hard on the highway, then pull off and immediately pop the hood, that's the time of maximum coolant temperature and pressure. Look along the top and bottom radiator seams (where the top or bottom tank joins the core). Look for 'steam' rising from the engine. Also, look for any coolant splatter on the front or top of the engine. It may be hard to see because air flow when driving tends to dry the splattered coolant.