Land Rover Repair: range rover water level, head gasket leak, exhaust gasses

Question
I have replaced rad. cap twice along with the themostat . the truck does not run hot but costantly have to add water in small amounts to keep the light out. I try to burp the system and add the water straight to the radiator.my model is 87 and the 88 has a place to burp the air out may have been a up grade? any Ideas?

Answer
sounds like a leak to me, if you're not seeing water on the ground anywhere in the morning you may have a slight head-gasket leak, sounds like a minor one though.  check your exhaust for water, and check the cooling system for exhaust gasses (can be done at a radiator shop).