Quick question...anyone know why the 5w-30 and 10w-30 weights of Mobil 1 Motor Oil carry the API "Starburst" symbol on the front of the bottles and the 15W-50 does not carry the symbol? Is that particular grade of oil (which, BTW is recommended for most temp. ranges for most E36's, according to the BMW manuals) inferior to the others? Wondering Ron Browne Bowie, MD