HI..I used to work for Subaru ..and sad to say I watched car after car after car, come in on tow trucks because of a over heating problem...its the phase one ej25 motor..its the only bad one ..it has a faulty head gasket ,,me and my girl friend have a 98 legacy limited gt sedan,that did the exact same thing as your car..I used to watch the needle go up!..then down. then up again .. the head gasket dosent seal right, causeing little air bubbles to seep into the coolent and causeing a vapor lock ..and whats funny , is the car will run perfectely fine .In fact it will pass every chemical test you give it ..cause none of the fluids will excape.only air ..we drove are's around for about 6 month's like this ..we had the radiator replaced and flushed the whole system ..ours blew at
98 k..Subaru denies any responsablilty for the problem .BUT~even the techs know that it is a defective head gasket ..we had ours replaced ..but we MADE!.SUBARU!.PAY FOR HALF..and they did..anyway ..pass this knowledge to anyone who has a phase one 2.5 PLEASE!..I really dont feel like typing to everyone who has one ..I worked for Subaru for 2 years In Renton WA.Walkers Renton Subaru..just thought you might like to know ..and it was $3000.but we had the whole engine replaced ..brand new..we had to pay $1500.and it was my employee cost .witch was $25 an hour shop rate....