95 Audi Quattro A6 wagon with 140K miles
The coolant reservoir empties every week. I travel about 20 highway miles each way for work. I don't see any evidence of leaking (i.E. Powder around visible hose connections, etc) and the car isn't overheating. The thermostat indicator light comes on, although the thermometer is less than half way. The problem arose one week ago and I am just adding water. How serious is this? Thank you from one more single mother trying to make it!