Happened to me too, B58 engine, there is a TSB for it. There is air somewhere in the system from the factory. Both of my tanks were completely empty, and there was some evidence of coolant dried around the cap. Dealer topped it off, has not come back (2500 miles and counting).
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21 G05 > 20 G05 > 17 G30 > 14 F30 > 08 E90
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