2003 Rover 2.0 ltr diesel 101 spirit

[John Grantham]

Hi everybody,
Having problems with cooling system. been in garage several times for losing water. Garage replaced fault core bung which had minute hole in it. Had pressure test and was sound. Replaced with new cap also. Since then water pressure gathers up and forces water through the screw thread of the filler cap. Engine constantly filthy due to this, and have to carry water everywhere. Seem to find engine runs slightly erractic, and the turbo has slight delay. This is when I know water is now coming through the filler cap whilst driving. Can anyone out there tell me whats wrong, as the garages seem to have given up on me. Cheers.