I've owned my 8 almost six years now, and the coolant light has come on twice. Both times at startup, on a cold morning after being parked outside overnight. (My car is garage parked about 362 nights a year.)

Both times, coolant level was below "FULL" (I couldn't make out whether it was below LOW or not), but both times I only needed a small amount of coolant to bring the level up to FULL.)

You guys think this is the stuck sensor issue, or something else? (Again, these are the only two times the light has come on - or, more exactly, stayed on, at startup. It has never come on while driving.)

 

I'm having the same problem. I thought the coolant level was low, so i added some coolant, but the coolant light stays on for a while, then it goes away, then it comes back again, then it goes away again...

 

It is most likely the coolant sensor. Just replace the coolant bottle. The sensor is basically a magnetic float shaped like a ring that sits inside the bottle. Over time gunk builds up and it doesn't slide smoothly and gets stuck. When I got my new bottle I could clearly tell the difference when you tilt the bottle. On the new bottle, you can hear feel the float move easily when you tilt the bottle. On the old bottle, it doesn't slide as smooth and would get stuck.