CJ and SM oils and ZDDP

[MBman]

New to the forum so if this has been asked before, sorry in advance.

As an avid old car hobbyist I have read the on-going dialog about ZDDP with more than a passing interest. As I understand it, the latest SM oil standard has a greatly reduced level of allowable phosphorous, something like 890 ppm. This has inspired much discussion about wear on cams, etc. in older engines and how this wear might be prevented. Somewhere on this forum I read that the new CJ oils, while also reduced in ZDDP, are permitted to have up to 1,200 ppm phophorous, which is the same as the old SL rated oils. Therefore, according to the writer in that post, the whole ZDDP and wear issue could be laid aside by simply using a CJ oil. This leads to my question:

If an oil is CJ and SM rated, like Rotella, which standard prevails, and how much of the ZDDP additive is permitted in the oil?

Thanks for your patience.

 

[TimVipond]

From http://www.api.org/certifications/engineoil/forms/upload/PartBFillable(CJ-4).pdf

"Phosphorus limits of 0.08 max and 0.06 min apply to API SM SAE 0W-20, 0W-30, 5W-20, 5w30 and 10w30 oils. A phosphorus limit of 0.10 max applies to API SJ SAE 0W-20, 5W-20, 5w30 and 10w30 oils and API SL SAE 0W-20, 0W-30, 5W-20, 5w30, and 10w30 oils. A limit of 0.12 max applies to API CJ-4 and API SH SAE 5w30 and 10w30 oils (SH must be preceded by a “C” category). If CF-4, CG-4, CH-4, and/or CI-4 categories precede SM or SL and there is no API Certification Mark, the limit for phosphorus does not apply. If CJ-4 precedes SM or SL and there is no API Certification Mark, the CJ-4 limit of 0.12 applies."

 

[MBman]

Thanks for the quick answer. Very helpful. I think I understand now.