I was looking at some NAPA 15w-50 full synthetic oil on sale for $3.29/qt, which sounds pretty darn reasonable. I found out that it is made by Ashland Oil co (Valvoline). What I find kind of odd is that it meets API SL/SM ratings yet carries Energy Conserving on the starburst label. What gives with that? I think it's the first 15/20w-50 oil I've seen that meets energy conserving ratings?