2002 ka problem that seems to start loosing water once warmed up, but by the time its loosing water it is actually steaming, wondered if a faulty thermstat could be at fault, it only seems to do it when water pressure has built up quite high
any ideas?

 

Not sure if this will be the case,but we had a KA that lost water, but no obvious leaks or head failure.

Turned out to be a common issues with the cap on the expansion tank, the rubber seal in it perishes or gets twisted and doesnt create a seal and so the water evaporated.

I refitted the seal flat again and it solved it. I did find out though that the fan doesnt kick in until the water reaches 105 degrees, which seemed odd, but when I let it run longer, it did kick in.

Was shocked out how much water evaporated and how such a small cheap fix sorted it.
Worth a check.