I'm getting the same indication this cold season here, as mentioned in a few other threads before. I'm a stickler for proper fluid levels, so I check my vitals every week or so. My coolant is always at FULL COLD before I start-up, but Tuesday night, we had temps around 15*F and winds 20-35MPH here and sure enough, I got in the car after sitting all day at work, and LOW COOLANT. Just needed a little, about an inch below the line when I checked.
But mind you, this was on the coldest day this winter season yet. It's really weird, it's been going on since I got the car, new Fluidyne radiator, new Stant rad. cap, new hoses, new water pump, thermostat, flush/fill new coolant, etc. System pressurizes good too!
No white smoke, no leaks, but where did it go?!
SS