Could you explain me this: if synthetic 0-w40, for example Mobil SS, is better than say 5-w30 (as I read in several posts), why would they bother producing 5-w30, 10-w30 and 10-w40 grades? Why not just use 0-w40 for all these applications. Is it all about volatility? Otherwise, it indeed has better cold flow and higher high temp. film strength and doesn't contain too much VII (again as I understood from some posts). Any other reasons ?