Disappearing coolant

The radiator stays full, but the resevoir level keeps slowly dropping. I check it every day before starting the engine, just to make sure it's at a safe level. After driving the resevoir might be an inch fuller. Never noticed bubbles.

Started having to add small amounts of coolant in November. November 16th, it was just at the low level line. Filled to 3/4 full. Took to dealership and block tested, radiator and valves pressure tested 12/14/22, filled to the full line by the dealership. Resevoir level slowly dropping, now at only 1/3 full, 3/9/23. Never lost coolant in the past.

The bipap valve was changed in 2020 after a couple of drops of coolant on floor, coming from the engine. No trouble until now.

 

Water pump

 

What he said. Check the bottom of the water pump, at the weep hole. Might be crusted up st the leak sight.