Well it is nuts, prism must have had his mystery leak solved, as for mine well no joy, when I last checked the coolant level, the top of rod was at MAX level when car cold. I drove 566miles/900km approx and then rechecked and level was halfway between max and min (which is still ok according to manual) but cannot for the life of me see a where it is leaking as the leak must be so gradual. A compression test sounds good but any trustworthy mechanics out here don't have the kit, and going to bmw I know they are going to fleece me and make me worry more....another thing that is a tad worrying is I took the coolant reservoir cap off when the car was cold and there was a slight hiss of air being released....now is this trapped air being released from the last time I topped up or fumes in my coolant system?


And if the cooling system is able to 'collect' air how the hell is it letting coolant out in the first place? a top notch diesel and I have to top up the coolant..

I also suppose the heater matrix / air con channels could be leaking but that would steam up the car I guess?all is clear....

That leaves like headgasket etc etc and that worries me although got no water in my oil, if it such a tiny loss would it collect anyway or dissipate in the heat....thanks guys for all the feedback this site is a great help...and I often know more than mechanincs about the ins and outs of the x5