Disco 2 Using water, ideas please?

Seems to be pressurising.

Expansion bottle cap, is this likely?

Personally, I'd change the expansion cap almost as a diagnostic measure first as last, they're cheap as chips anyway.
How hard are the hoses getting? Very hard hoses could be an indication of engine gasses finding their way into the cooling system.
Air locks can cause coolant loss, but if the system has been OK for some time, then suddenly starts losing coolant I would be tempted to suspect the failure of some part or other rather than just an air lock.

You know the answer and you wont like it!
Keep an eye on the rad as that will start leaking next from the pressure.

Pipes are firm when hot but not hard.

Cap had loossened it self slightly

MJI said:

Pipes are firm when hot but not hard.

Cap had loossened it self slightly

Click to expand...

Have you checked the main pipe going into the cylinder head with the temperature sensor in it?

Those leak all the time, take it off, clean up the crusty crystalised coolant, get a jubilee clip and do it up FT!

Also, how much is it using?

lynall said:

You know the answer and you wont like it!
Keep an eye on the rad as that will start leaking next from the pressure.

Click to expand...

Nah, top hoses split first. I know that only too well....