Fitted the new core plug, new thermostat( what a b*gger that is to replace)... took my time filling it back up again.
First time idling it started overheating again :frusty:

Gently pulled back the small hose (from top to t-stat) let all the air and steam escape.
Filled up the exp tank again and all is fine now
Temp gauge sits on half and stays there.

Many thanks to all who were so kind to help me.
Much appreciated

well done fella enjoy it for now