Range rover v8 3.6

It doesn't always leak.

Is there such a thing where 'some' water could leak out, but leave some in as the RR runs ok. Doesn't overheat, gauge stays at 12 o clock.... I top up reservoir when cold It leaks out from the back I of the engine, then stops leaking and still runs......

If it only leaks out when cold sounds like the leak seals up with expansion as the motor gets hot.

Head gasket??

The only other answer i can think of is that one side of your V8 the head gasket has gone. It won't show up so much when the engine is hot as the exhaust will be so hot it will keep it as vapour rather than visible steam, but if you are constantly loosing coolant - that is where it is going, check coolant hoses that are routed around the engine aswell

You can try getting a garage to test it by checking for combustion gasses in the coolant.

Ok.
Thanks for all your input guys.
I have a mechanic looking at it on Monday now. I'll let you know what we discover.

Get some UV dye and a torch?

Did your mechanic solve the issue?

Yes. It turned out that, when he stripped it all down, the pipe had come away from the thermostat housing. He connected it back up put it back together. Topped it up with coolant and it's been fine ever since.