Hi there. I have recently had a new head gasket fitted in my T4, the cylinder was skimmed and the cam belt refitted. Prior to that I had new pipes put in as there were some splits and we replaced the thermostat and the housing (for the sensors). For some reason the water in the cylinder tank (I'm not technical, not sure if this is what it's called) keeps dropping. It's not coming out as steam and there don't appear to be any leaks. When I unscrew the cap there is plenty of pressure in the tank. Has anyone come across this before? My mechanic is stumped!!