massive coolant loss
 

'00 X5 4.4 130k. So it just started losing a half gallon + of water (I'm not putting coolant in right now) per day, driving maybe 60 mi. There is no white smoke, normal power, and no visible leaks at all. Nothing on the ground. Recently replaced expansion tank cap, water pump, and thermostat. Any ideas where that much water could go with no obvious sign?

You say cooling stuff was replaced recently so my guess is it was never quite filled to capacity.

no dude, I do all the work on this car. If I'm having to put a half gallon of water in it every day, whatever it was full of a couple days ago doesn't really matter. What I'm asking is: if it's not going out the exhaust, it's not leaking somewhere visible out on the ground, where else can it leak from? while driving of course.

May need to pressure test it and look from underneath with the underpanels off... That is a decent amount of coolant loss, it could only be leaking under pressure while driving though making it hard to just see with a quick look.

Have you checked your oil ?I dont think however that amount of water can be getting into there without any other symptoms. You could also have a sniff test done to see if you're getting any carbons into your water system which could indicate head gasket/cracked head. But again you said it was running fine :dunno: just mulling it over....