Check this document out
https://rotella.shell.com/en_us/pro...e31c1a45ba16a94dded7f4aea73/t6-sae-15w-40.pdf
Rotella T6 is CK-4 certified
but nowhere in the document mentions that is is SN or SM certified for gasoline engine. Not even JASO MA certified. It just happens that diesel engines require higher viscosity oil and this T6 is one of the best out there for diesel engines.
Motorcycle owners see this full synthetic T6 in the viscosity that matches the requirement of motorcycle engines with wet clutch, at very good price compare to motorcycle oil, so most of them switched to this T6. Many motorcycle owners swear by this oil. And I somewhat agree. I used that T6 once in my '13 RTL until last spring when I changed the engine oil I switched back to Mobil1 5W40 European car formula. Engines in the Spyders were designed and manufactured in Europe by Rotax so using Euro formula oil seems to be a logical choice.
No Offend to anybody here, just my own experience and opinion.
Cheers!