hi I have a vaxhall victora 1.8 sri the water level drop. so top it up ok for 2 days then top it up again. pressure test it the the pressure never drop .then it was for ages then it happened agan sumone it cud be the cap so got a new one .sill drop .top it up pressure test agan no drop again. at my wit end .can eney one help .

Similar to the pressure cap (which I was going to suggest) is any other source of leak, even the slightest amount that is hardly detectable could lead to the drop in pressure but if the coolant is being consumed then I would look at the cylinders (take plugs out and see if water contamination present) or if mixing with the oil.
Possibly worth throwing a tin of coolant sealant into the expansion tank (any porous castings usually sorts it)

hi there thanks for that I will look it the things u said . there no water leak as fare as I can bin all over the engine with a tuch. no water .thank u for a your help.