Likely a head gasket issue, especially if this is a 2.5L DOHC. The head gaskets on the 1998 Phase 1 Subaru 2.5L DOHC engines have a high failure rate.
We had the same problem with our LHS. We first replaced the thermostate and it still happened. So we keep looking and the lower radiator hose was colapsing. You might check the hoses after you replace the thermostate. Hope this helps.
your thermostate needs to be replaced
Try replacing the radiator fuse relay
You need to check coolant temperature sensor and the water pump.
head gasket leak or thermostate needs to be replaced
I replaced my 1996 radiator on 2006. I tried yellow pages and found a new/aftermarket one for less than $100. You might want to replace the thermostate as well. Good luck.
When the thermostat and radiator were replaced, coolant could have dripped into an electrical connector or a sensor could be disconnected or damaged. Check the temperature sensor and crankshaft sensors first.
you need to replace either your coolant temp sencor or it could be your thermostate...but most likely it the sensor...i had this prob and i just replaced both to be safe
Be careful there is a temperature coolant switch mounted next to the thermostat housing. I thought this was the sensor and replaced it by mistake. There is another sensor.
the hoses leading to and from your radiator might be clogged. If you had a rusty radiator, the rust may have clogged the hoses that carry the coolant. you should check all your hoses and even flush them out.
If your heater core wasn't leaking at the time your radiator was replaced , then ( no ) That would be two separate jobs
I have a 2004 kia Sorento and just replaced the thermostat. Follow the bottom hose on the radiator up to the engine, remove the two bolts that hold the thermostate case to the motor (you can remove the hose from it if you want to, I was lazy and left it attached) and the thermostat is right there.