hi guys firstly the head gasket has been done with mls gasket ages ago with cam belt and bolt kit ect ect and has ran fine since over 30k ago,any way the other day i thought i would do a coolant change with all the rocomended coolant i.e oat long life coolant (the red colour stuf).at first after i done the change i suspected a air lock so i bled the system as recomended ran it with blowers on hot and then finaly i started gettin heat through the blowers,its been fine all week then today i noticed the coolant fan cme on when driving about 2 mins after starting the engine then went of 2 seconds after turning engine of.it has been doing this all day and nite,the temp gauge never moves above half way(normal reading as always)ive checked pipes ther all hot and the watter seems to be circulating through the header tank fine small hose at the top, the car was fine before i did the coolant change any advise would be great thanks.ps no coolant loss of leaks but obviously the problem has accurd since the change,wish i never started.thanks again