After turning a corner the other morning, my 2013 T5 gave a low coolant warning. I pulled over and put in some distilled water, looking only at the MIN level and bringing it up.

Drove home that night and allowed the engine to cool for about 3-4 hours or so. I checked the level and it was on MIN and on MAX at the same time. You could see a clear step in the blue-green fluid of almost 1"

Now clearly, there are multiple chambers or baffles, for de-aerating or whatever. I haven't been able to find any info on this.

So the question is, when is the best time to check the level and why aren't MIN and MAX marks on a common chamber? The following morning, they were back at a common level.

Is that step in the fluid telling me the system has a big air bubble somewhere?

Den