Intermittent overheating of 2000 subaru forrester

We have replaced the thermostat and pressure tested for leaks. The car only overheats after 90 minutes or more of highway driving. When it is cooled down it shows no sign of what might be causing this problem. As the car is being driven by a young mother of a two year old with cerebral palsyin the far reaches of upstate New York, this is a very truobling issue. Any suggestions or help would be extremely welcome.

Thank you

Does the car lose any coolant? This could be the start of a head gasket problem. How many miles on the car?

Yes it does. The car has somewhere in the neighborhood of 55,000 to 60,000 miles. It is a 2.5 L engine, which as I understand it, is prone to these problems through design flaw.

sounds like a head gasket issue to me.

subaru offers a coolant additive that can sometimes help stop this problem on the 2.5 liter (EJ25).

contact the local subaru dealer and add this to the engine. it should help. always start with the cheapest option first.

hopefully the car hasnt gotten hot enough to damage the heads.

Thank you very much. I’ll look into that.