Hi Just recently done the head gasket on my 2001 bugeye wrx all went well with new steel gaskets fitted but a few days after the themosate went on it causing the car to over heat i had a spare one so replaced it all was ok till today started to over heat again iv taken thermosate out and its working fine do's anyone have any ideas whats up with my car also when it over heats it starts to fill up the coolant bottle hope someone can help

 

when you say its filling up the coolant bottle, is it just rising or bubbling?

If its bubbling then id get a block/sniffer test done to see if theres any exhaust gases in the coolant....

 

also id double check you dont have an air lock in the coolant system.....