v8 always loses a little coolant

My 99 3.9 Disco 1 always loses a little coolant from the header tank, it seems to want to settle about 1/2" below where the + is for correct coolant level, the header tank is a replacement clear one, is this something to be worried about (i'm paranoid about liner/block failure).
It never seems to lose anymore then that maybe just a slightly different tank then the original?

Some RRC tanks were white opaque but still the same as the discos black one. The cold level is where the half way seam is, or just over the top of the raised level marker that may be seen inside the tank.

Thanks discool, I replaced the said black tank about a year ago due to leaking around the seam. I got a semi-opaque white one (nicer).
It never looses more coolant then just below the marker no matter how long it is driven for, it then maintains that level, hopefully its just me being fussy, the car is fitted with a gas conversion and the expansion tank may well be aftermarket, I can't remember TBH, sometimes after I've parked up I can just hear the cap hissing a little

When the coolant is under pressure, the hoses will expand and the coolant level will drop.

If the cap is hissing, get it changed and that will probably cure the issue.

Peter

Thanks, I'll get a new genuine cap, Probably a britpart one on there at the mo!