I have a 2003 wrx and ive been running it with a mishimoto radiator and a gutted thermostat. recently i put a thermostat in the car, a gates, and it overheats now. I dont know whats wrong maybe the gates thermostat is no good, it doesnt open enough?
Let car go stone cold. Keep engine off. Open turbo reservoir cap, and squeeze top hose to release air. Repeat until the cows come home. Then repeat some more.
Turn motor on, stay away from fans at all times (!!!!) and repeat again.