"1995 Subaru WRX: Radiator Overheating Problems"

White 1995 Subaru WRX Front View

The temperature gauge on my 1995 Subaru WRX is rising to 3/4 way hot after a good drive when I park up. (It does not always happen) Some coolant comes out the coolant expansion bottle on the passenger side of the car. I’ve just had the head gasket replaced and fitted a new radiator. The only 2 things left that could be causing the problem are the thermostat (which is new) and the water pump, could a faulty pump cause coolant to be pushed out the overflow and make the temperature gauge rise?

Answer: The cause is pressure in the cooling system as you correctly identify. Yes it could be head gasket. However, you mention this has been renewed and if the work was done correctly then it should have been OK. It could still be related since in many cases the cooling system has not been cleared of air after a refill. This causes the pressure to increase in the cooling system (air expands when it gets hot) and then pushes out the coolant. By refilling each time, maybe even overfilling, this problem will persist. Only fill the header tank to the prescribed level and NO more.
Are you getting any smoke or steam out the exhaust? Tell tale of head gasket problems.
Additionally check for signs of water in the oil.
Finally you need to get a compression test of the engine, this will indicate if there is a head gasket issue. Don’t just go around changing things like water pumps, test first then replace the cause. This does involve some technical testing only completed at dealers.
Best of luck ….