Also:

Apparently it's not the API-SM rating that restricts ZDDP. It's the ILSAC GF-4 rating that does it. None of the Rotella I saw last night said anything about the ILSAC thing.

Quote
Stolen from this thread on some Caddy website
Actually the ILSAC GF-4 standard is what puts limits on the amount of ZDP in the oil NOT the SM standard. The SM is an API performance standard that does not limit the anti-wear capacity of the oil. The API starburst symbol (GF-4) that states "for gasoline engines" is an indicator of reduced or controlled ZDP levels and the addition of fuel economy improving friction modifiers in the oil. That has nothing to do with the SM performance spec per se.

This is then why the "diesel oils" like Rotella/Delo/Delvac can be rated SL/SM for API performance in gasoline engines and have the higher ZDP levels. They are NOT rated with the ILSAC starburst symbol "for gasoline engines" because they have the higher ZDP levels and they do not contain the friction modifiers for fuel economy. Those oils are simply "very good engine oil" that meets the latest gasoline AND diesel engine oil specifications per the API performance standards. They are marketed as "diesel" oils simply to draw the distinction from the ILSAC starburst "for gasoline engine" oils.

Any modern engine is designed to easily run with the reduced ZDP level of the ILSAC GF-4 oils. Older and specialty engines still need the additional antiwear protection that the Delvac/Delo/Rotella oils offer.

The last time I looked at Mobil Extended Performance oils they were specifically NOT rated with the ILSAC starburst for GF-4 because of the higher ZDP content and lack of friction modifiers.

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