Pressurising coolant

[Frosty]

Sorry about hijacking your thread Danny but it saves starting a new 1 for a similar problem

I got a pressurising issues with my car. It drives fine etc and sit at 75 ish under normal driving and goes up to over 90 when boosting on with is normal yeah? But the cooling system is getting fair pressure in it. I cant take the rad cap off after driving it with loads of coolant escaping unless I let air out by opening the bleed screw next to the fuel filter. It never over heats and doesn't seem to use any water.

I fitted a victor reinz head gasket and bolts and had the head pressure tested and skimmed when I rebuilt the engine about 4000 miles ago.

Any ideas would be very helpful