98 wrx type r, had 2.5 conversion recently, but then split hose caused loss of water then head gasket failure. ive had the head gasket sorted but now getting over heating problems after 4-5weeks, temp guage started to rise to 3/4 then fall to below 1/2, water coming from breather on filling tube, and air bubbles up tube also, had water movement noise inside car behind dash on starting up car also. am thinking head gasket again but if so what has caused this again? any ideas/ suggestions appreciated, thanks.

 

air lock?

 

any ideas on how to clar an airlock?