Coolant Level Warning in Cold Weather

I know winter's coming here in MA because the coolant level light has begun coming on on startup when the temperature is below 40F. It goes out if I restart after a couple of miles (i.e., if the engine is warming up). I'm not losing any coolant. The reservoir level is normal. It appears slightly lower on cold mornings which I take to be contraction. Adding a slight amount of G-12 up to the mark doesn't solve the warning light phenomenon. (I obviously don't want to overfill).

This is only slightly annoying but it's been doing this for three winters now. I've searched the forums but haven't seen anything which describes this.
Any ideas?

This has been posted before, do the search using the boolean method. I can not remember to cause. Check your coolant before you start and make sure it is up the the proper level. I almost think that the previous post concerning this were a below proper level problem. Have you checked for coolant migration? You sure do not want it.

When I had this problem, it was just that the coolant was a bit low. If you look into the bottle with the cap off you can see whether or not the sensor is covered by coolant and confirm this.

Top up the reservoir with some distilled water. The coolant shrinks slightly in cooler weather, enough to cause the CLW to ding at you.

If that's not doing it for you, check for coolant migration or replace the coolant temperature sensor.

scurvy

This happened on my '85 Jetta. I removed the level sensor and wiped clean the probes and then it worked. My take is that slight changes in resistance will cause false readings.

--Nate