I have a 2000 Subaru outback, every time I drive over 65mph the car start overheating, if I slow down the gauge goes down. I replaced the water pump, thermostat, and radiator and the problem is not going away. Both fan are working. Hope this is related or may help- Seem to add about a quarter a gallon every other day. Also if I open the radiator cap after a along drive there is no pressure coming out of the radiator.
It sounds like either you have a coolant leak somewhere within the pressurized portion of your system or your pressure cap is failing (optimistic guess). Another good possibility is a blown headgasket (pessimistic guess).
Have the cooling system pressure checked, and either replace the radiator cap or test it. Also, check your coolant for evidence of hydrocarbons and/or have a pressure leakdown test done on the cylinders.
Post back with the results.
I replaced the radiator cap, so I am not loosing any more coolant, but now I get coolant odor when i have the heat on. Sometimes when I drive on the highway it start overheating but if I slow down it cools down.
Tardis may be right…Known problem with that year Sub…
Leaking heater core?
burp the top radiator hose after you fill the tank and run the engine up to normal temp. Also check for a partially clogged thermostat, and if there is a clutch fan on the pump, make sure it is working right, if electric fans, are you sure they are turning on and off at the proper times?
I replaced the thermostat but seems the electric fan are not turning on regularly.