Just try to spread my good experience and render some hope to other Subi owners with heating problems.
My Subi starts to overhead after I replaced t-belt, water-pump and thermostat (stant). Thought was stant t-stat problem, took it out, boil tested along with a new oem t-stat. Both t-stat appear to be opening up just fine...
Then I read posts here, people talking 130k is common for Forester 98 (Gen I) to show overheating with Head Gasket leaking. I checked, could not see much bubble in overflow, maybe one or two just after stop. (that's normal i guess), exhaust does not have much water spray, one/two drop when start in the morning. However, I do notice upper hose is warm yet lower isn't. (So the t-stat by stant is strange?).
My solution was replace the t-stat with OEM. Then a good mechanic friend of mine worked on Subis brought a vacuuming device to suck out air pockets in the radiator. (Same device to suck out pockets in my break/cluth fluids.) We refilled with 50/50. Viola, the car runs great now and temperatur is just stable right at 35% of the range.
I guess I was very fortunate to have a good mechanic to diagnosis and tried cheap method before jumping to conclusion of HG. Though I will be watchful of it, and may try steelseal in future at first signs of syptom.
