I don't disagree but strangely 10w-30 is allowed which is available as a conventional. Rotella T4 and Delvac 1300, both meet CES 20086. Our 6.7 is solid lifter, so no dog in the fight.Because they assume that as a whole the 15W-40 oils will be of inferior quality to those that are 5W-40 at least in terms of base stocks. It’s an easy way for them to communicate this to their customers.
It seems like a better way would be to make it a part of Cummins CES 2008x, rather than all the confusion/stigma about cold flow in the bro diesel truck communities.
Our Mazda, likewise, was spec'd 0w-20 due to the OEM's desire for full synthetic, so the concept is not new.
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