Temp gauge went up and down and finally into the red. I checked and found no leaks, fan was working, neither the a/c or heat was on, coolant level was good, radiator is about 2 years old. I'm hoping it's as simple as a thermostat problem. If so, where is it and is it easy to replace? I'm not a mechanic but not afraid to try if it's "reasonably" easy, meaning I don't have to put the car up in the air and it's possible to just have to crawl underneath.

Yeah its pretty easy. Two bolts on the water pump (attached to lower rad hose) and pull it out. It will drain all of the coolant so be prepared for that. Make sure you use a Thermostat from a Subaru dealer and you "burp" all of the air out of the cooling system. May also want to change the rad cap while you are at it.

 

I think your car needs the Subaru Coolant conditioner (less than $2 from Subaru dealer) added to radiator? May help with external coolant leaks.

There is also an aftermarket thermostat that is acceptable, made by Stant. There is a stickey about it. It comes with the gasket. I just ordered one from Amazon for $15.

odd symptoms for this motor, it usually has other associated symptoms - have the headgaskets ever been replaced (common issue for this motor)?

 

when it overheats - do you have heat in the cabin area or does it get cold?

 

any recent work? if the coolant isn't properly bled they can overheat.

 

about a gallon-ish of coolant dumps out when replacing the tstat so be ready. from the hose side when you pull that off then another smaller gush when you pull the stat out, goes everywhere, be ready.

 

if you replace the tstat - be sure to bleed the coolant properly and be prepared for another overheat event right after the replacement since air easily gets trapped in these cars. some of the radiators have a plastic type screw on the top passengers side of the radiator. loosen that and keep adding coolant until air bubbles stop coming out, then tigthen screw, finish filling. otherwise read the other threads about bleeding or burping the system. you'll need that after replacing the tstat.

What they said. The only other thing that would be good to know is how many miles are on the car (to know what may/may not have been done to it).

 

The burping of the system, as Grossgary said, is critical... search the group for instructions on how to do it (lot of people have problems doing it right)