Hi my 94 wrx started to overheat this week. I found that a small pipe had perished under the engine. I replaced it but found that it is still overheating. I replaced the thermostat but that hasn't made any difference. I have tried to get all the air out by the usual methods. No change. There is no white smoke, no water in the oil or oil in the water. It runs fine on tick over and when stationary but soon as I drive it within 3 minutes it gets hot. I do have bubbles coming up from the header tank and when it gets above 3/4 he way to hot it bubbles a lot!

Any ideas?

Fingers crossed not a head gaskit!