'90 Subaru Legacy overheating....

since you loose the radiator drain plug and screw it back in I believe that on the drain plug there is an "O" ring which it gets either harder or cracked. Just renew the "O" ring or the drain plug.

Well it sounds like you have covered most of the bases.
One thing that could cause overheating is a restriction in the exhaust.
Do you know if the radiator fan is coming on when the engine reaches 220 degrees ?
How long can you drive it before it starts overheating, and does it boil over when it does ?

hi it could be a faulty water temp sensor, however if the car was overheating you would notice as it would be gurgling or steaming in the engine bay somewhere, it may also be a sick water pump or cracked radiator

On my 1998 subaru legacy outback limited I replaced the thermostat and did a radiator flush and fill and it overheated when I tested it. It basically overheated because there was air in the system. I relieved it by running the car and partially unscrewing the black plastic relief screw on the top left of the radiator(looking at it from the front of the car) until it stopped hissing and fluid started coming out then I screwed it back tight and I've never had a problem since. I think subarus are pretty fussy with this because my mechanic even missed it when they did the head gaskets.

When a car overheats it's rarely the thermostat. They just don't go bad that often. If it overheats when you idle a lot, it's the fan and with electric fans, it's almost always the fan motor. But to find the thermostat, follow the top radiator hose to the engine and there it is.

Have you checked to see if the radiator fan works? And have you checked to see if the water pump works? Two very important items key to overheating.

The thermostat is mounted low down on the bottom of the engine where the large radiator hose connects to the radiator. The housing is bolted to the engine block and the thermostat is inside. Don't attempt to replace it unless the engine is cold otherwise you will burn your hands. Make sure you bleed all of the air out of the system before driving off.

1988 subaru clean out radiator for summer diving

well....if that stopped your overheating problem, that's good, but todays engines depend on running at a certain temp. for proper performance, gas mileage, etc. We can thank unleaded fuel for that....

Multiple causes for overheating. Start with thermostat.

I had an overheating problem in my Subaru that ended up being a head gasket (I replaced thermostat and radiator, but these did not help). It turned out that the head gasekt leak was allowing air into water passages that prevented water circulation in the engine.