97 Mazda B2300 coolant loss

Reman engine (8plug, 4cylinder) loses a quart of coolant each week. Dealer who installed the engine replaced radiator, fan+clutch also. They can’t find a leak and neither can I. Guage reads cold, but it did that before the old motor blew out. Where the heck is coolant going to?! I don’t want to blow out the motor, can anybody suggest a cause? Thankyee!! Jimbob520

I can suggest how to FIND the leak.
There is a UV sensitive dye available that can be added to the system, then a blacklight will cause the leak to glow.

Can I assume the engine has been tested to ensure there’s no headgasket breech?

Also, find out why the gauge doesn’t work. It could be a cut on a wire or a disconnect somewhere. Thst gauge is your first line of defense.