Correct me if I'm wrong but I believe BMW (and other European car makers) require phosphate-free coolant. Ironically, I just bought a gallon of BMW coolant today and read the ingredients. Phosphate-type chemicals are not listed. I'm pretty sure the metal alloys used in the cooling system are not compatible with phosphates.....they attack and damage the metal and seals.

I avoid the normal store bought coolants whenever I deal with a European vehicle. Always buy the OE coolant or an equivalent European brand.