My days of experimenting with different brands and viscosities are now pretty much at an end. I am using Shell Rotella Syn 5w-40 in all my internal combustion engines, ranging from a 2003 GMC Duramax diesel to an old Infiniti Q-45, a 32 year old BMW air cooled twin motorcycle, and even my Generac air cooled 15 kw back-up generator. The viscosity range allows the use of this oil throughout year here in cool Vermont. I have about 25 gallons hoarded away. The sad thing about looking for the Holy Grail is that, if you find it, there is nothing more to do.