I am facing a perplexing issue, my car, Audi A6, 2002 2.4L has the following issue.
Coolant level drops, obviously there is a leak but after replacing the water hose, the water pump etc etc, the leak persists though minimally. BUT here is the real issue, when the AC is running on the highway, the coolant level falls very quickly and the indicator for low coolant level starts to flash, the gauge does not go past the middle though, for sometime.
I usually stop and put water in the coolant tank and the cycle repeats itself.
WHAT SHOULD I DO PLEASE?

 

Have you check the reservoir, they dry up and crack over time and leak with out you know.
AC pressure speed up the leak, because it's cycling the coolant through the engine and sometime pushes back some of the coolant to the reservoir. Check the bottom of the reservoir.