Thanks guys. Will get into the pump as soon as rain stops. I have a nasty feeling that a leak from the head gasket is pumping air into the system.
BUT has any one heard of this "boil the 'stat before fitting" caper ??? The advice comes from my parts supplier who has worked with BMW s since the sixties. Quote "It often takes to or three goes as they are hell to bled"
Did not fit a whole new system in a one er due to the fact that she was ok with a new rad for a couple of weeks, THEN the 'stat seemed to stick one day...... ho hum
Anyway a nice engine to work on so if the head has to come off it comes off !