Castrol Syntec 0W-30 is much thicker at normal operating temperatures than the Castrol Syntec 5W-30. The Castrol Syntec 5W-30 is too thin for use in BMW vehicles that require 5W-30, but the 0W-30 is fine for those cars. The Castrol Syntec 0W-30 is too thick fo... Login to read more.