No, those, including FD are the highest ratings currently. Exactly what in those specifications specifically addresses the formation of valve deposits in a four stroke engine? Ultra is "only" FB rated, yet is known to be one of the cleanest running two stroke oils available, outperforming many FD rated oils. FB, FC, and FD have the same lubricity requirements. FC and FD add cleanliness requirements. It would appear that it is more complicated that just having an FD rating. https:/
Originally Posted by Kamele0N
Why? Is there any "higher" standard than JASO FD/ API TC+ TiSi ISO L-EGD etc...?
Originally Posted by edhackett
That makes it even more important to run the Stihl Ultra. It was specifically formulated to minimize valve deposits in these engines. Ed