I have a 2007 Mazda6 with 3.0L V6. I had coolant changed while in for routine maintenance two months ago. Since then I have noticed the radiator fans running under conditions that they never did before. So I checked the coolant reservoir and found it effectively empty (i.e., below top of low hose):
I added distilled water to the reservoir to bring it to the
F line. After a few days I checked and it was back to virtually empty. Today I filled it with distilled water again, immediately drove just 2 miles, popped the hood and yet again the coolant was back at the level shown in the picture above!
I haven't noticed any coolant leaks where the car is routinely parked.
The ECU has not indicated overheating even on long drives at high loads in extremely hot summer weather.
Do I have a problem if the coolant is persisting below the
L line in the reservoir? If so, what is recommended to diagnose what's going on?