note specs
the level of zinc -can- be higher in 20-50 grades as this is too thick for newer car engines that need lower levels for their catalytic converters, so is exempt the limits. all othergrades are 12 ppm or less (sg, 10ppm sf/sl). note unlike most things the grade denoted on the can is a -maximum- grade. ie if it says sg only then is likely to be better than one that says sf sg and sl as it cant comply fully with sg if it meets sf and or sl. try to avoid too wide a range eg 0-40 . and yes go find a diesel oil such as shell rotella 15-40. sg rated.. note this info is biased for air cooled engines.
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