1997 SUBARU LEGACY L OVERHEATING HAVE CHANGED OUT EVERYTHING BUT THE HEATER CORE. T-STAT,RADIATOR,WATER PUMP,HOSES ETC. I HAVE EVEN REPLACED THE HEAD GASKETS AND HAD NEW VALVES. STILL OVERHEATS. REPLACED T-STAT FOR THE THIRD TIME BECAUSE IT SEEMS AS THOUGH IT IS NOT GETTING FLOW. HOSE UP TOP HOT BOTTOM HOSE COLD AS IS THE RESERVIOR FLUID. ANY HELP WOULD BE MUCH APPRECIATED!!!

SOURCE: '97 subaru overheating

head gasket most likely.

SOURCE: 1990 subaru legacy

make sure you bleed the air out of the system on the top left hand side of the radiator or the car will overheat due to air lock

SOURCE: Overheating 93 Subaru Legacy

water pump could be bad again. if the seal is out lets air in around pump propeller and it won't move water and it over heats. its a lot of work but you can fix it your self

SOURCE: 1990 subaru legacy

I hope this helps : A lot of people, even mechanics overlook the dramatic effects of "air lock" as described above. This is especially prominent in BMW's because they seem more "picky". Your cooling system (every cooling system) is balanced just well enough to nearly always keep your engine cool when operating properly. Sometimes a pocket of air does become trapped at one of the higher points ion the system however. This air pocket acts like a blanket trapping heat in the one dry area, in addition to impeding air flow. I would start WITH THE ENGINE COLD, by adding a radiator flush tee in to the heater hose leading to the intake. Start the car with the flush cap off, and the radiator cap. Play with the hoses and try to keep this tee higher than the fill cap on the radiator, to let out any air. When water is seen at the tee, cap it off and fill the radiator all the way, with the engine running, as to fill the entire block. Keep in mind that with the engine running, you kind of need to hurry. In only a few minutes, the water will get hot enough to start spewing from the open radiator (don't worry you have plenty of time, assuming it's all the way cooled down) I have seen many people leave their radiator half full, because it takes some time for the water to trickle all the way down through the runners on the radiator, and it looks full even though there is "air" (it's technically hydraulic pressure, like a siphon) holding it up. Hope fully that is the problem. You already re- did the whole system. Check your igniton timing too. Sometimes that can contribute to an overheat as well.

SOURCE: 95 Subaru Legacy overheating, top rad hose is hot,

does your heater work? if not than your thermostat is stuck. be careful not to get the car hot as those engines are sensitive and will warp the cylinder heads quickly.