I am not sure if anyone has mentioned this, but on some other cars I have known the header tank to have a leak - does not show up really until car being driven so system under pressure - usually a crack near the pipes connected to it.

Such leaks are normally easily spotted by the dried coolant on the outside of the header tank (speaking from experience) V8 or else ...

for what its worth my 2005 FFRR vogue V8 4.4 has just suffered this same issue.
I took it to my local mechanic and after a week - i said i didn't need it so take your time, he eventually eliminated all the air pockets by ….
raising the front end as high as possible on the lifting ramp, topping up, removing the breather screw, until it bubbles out, then taking it for a 1 mile or so run, letting it cool down, and repeating the process.

Hes a damn good bloke to know, ex Landy engineer at their works.

First off hello to a fellow cornish ffrr owner, im far west how about you?

Anyways the job in hand, todays the day, new car tax bought lets hit the road for the first time, tyre pressures checked, levels checked filled up with fuel and a new 200 cap in place. 7 mile round trip faultless. Took it home and got stuck in traffic for no more than five mins, temp gauge went into red, check coolant temperature message was displayed so i put heater on full and gauge came back to middle. Stopped as soon as i could no more than half mile later. Looked under bonnet couldnt see nothing obvious so continued driving. Did about 30 miles home and end of my road low coolant message appeared. Pulled up home and again no obvious signs of leakage. So assumed air lock causing gauge to go in red and by time i got home air was now in header tank meaning low level. All sounds good?

Just been and checked level now its cooled and looked in tank and put my finger inside and all around the inside has got like a grey grease all over it. Ive topped it up by a pint and half so we will see what happens tomorrow...

Anyone know any reasonable quality/priced head gasket suppliers?