System is full when the "pecker" sticks out. The low warning should come on when more than a pint or 1-1/2 low. If you have a low coolant warning when there is coolant you can see in the reservoir, something is wrong with the sensor system. (unplugged, stuck float, etc)

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)