Could be. The main tank is not heated, and the stuff freezes at 23 degrees, i.e., no automatic pumping from the main tank to the heated tank if it's been below 23 degrees for a while. I have no idea what strategy is used to regulate the pumping, but I suspect it is either a float or electronic level measurement, that pumps a slug of the fluid from the main tank to the heated tank when the level gets down to a trigger point in the heated tank.


BMW does warn that in prolonged cold weather, the heated tank may have to be refilled manually every 2-3,000 miles.