losing that much water should be easy to trace.can you smell curry powder?sounds daft but if its leaking then this is how it smells.if you have a small hole in a rad pipe then you wont see it leaking,check under the dash to see if its wet there.if it were burning that much then it will be smoking lots of white smoke.check condition of the oil and even condition of spark plug.look around the engine with a torch and look fot rusty stains.failing all this have it pressure tested.check also the breater pipe from the expansion tank as it could have air in the system and be spitting it out
mikec
April 2009