I have a 2000 Subaru Legacy that overheats!

Make sure that the radiator is not restricted. Using a inferred thermometer make sure all the cooling tubes are cooling. Make sure there are no air restrictions between the condenser and radiator.

Most likely you put the thesmostat in upsid down. Good luck

Two things would cause this

There is a slow leak and the radiator is low on fluid

Let the vehicle cool down completely and then check the level in the radiator. I bet its pretty low. Top off the radiator with a 50/50 mix of coolant and water. start the vehicle and let it warm up with out the radiator cap on. Keep adding fluid as necessary. While waiting for it to warm up check around for any abvious coolant leaks. Things like hoses, radiator seams, water pump, water inlet/outlet gaskets. If no leaks are found it may be necessary to pressure test the cooling system and even then it might be a slow leak that only occurs when the vehicle is cold.

If the radiator is full than I would suspect that water pump is no longer working or creating enough flow. If the thermostat where stuck you would still get heat. If the water pump is not circulating coolant than you would get no heat and the car would overheat.

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You probably need to change both the water pump and the thermostat. Otherwise check you're spark pulgs. If you've blown a head gasket, your vehicle will overheat. Pull the spark plugs and if you have one plug that's nice and shiny, it could be that you're leaking water into that cylinder and you've steam cleaned it. I would then do a compression test.

How about the radiator cap?

Pretty common on subaru's, try elevating the front of the car whilst bleeding the cooling system.

Both are for the radiator and should be working.

Im wondering are your fans strong enough to cool down that aluminum radiator.

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.

Both head gaskets have to be replaced and the heads need to be resurfaced, be sure you go thru the torque specs and sequence correctly, it is a strange process, but has to be done. subaru puts out a product called cooling system conditioner, it's advised to install this.