We can cut thru the clutter and should be able to agree on one point, the primary motivation for OEM recommendation of XXw20 oils has a lot to do with perceived fuel economy. Even a casual look at articles in industry publications, the new diesel oils, CK-4 and especially FA-4 (which is centered on XXw30 oils as opposed to traditional XXw40 oils), has a primary focus on fuel economy. Any other perceived benefit takes a back seat. I don't doubt that the lighter vis oils can do a good job, but that doesn't mean they do the best job. Even on commercial diesels, they are having to redesign the motors around the new FA-4 oils, which have a lower HTHS rating, so that internals are such to compensate function under lower HTHS standards. So it is clearly acknowledged that the new oil is inferior in at least HTHS to previous specs, but now we are going to put it on the engine itself to take care of itself since we are removing a level of engine protection from the oil. All in the name of some greenie idea of better fuel economy. OEM HTHS requirements for XXw30 oils for heavy diesels has been >3.5. New FA-4 oils? Now 2.9-3.2 max.
We are dealing somewhat with the same thing regarding the 20w vs 30w issue. Not exact same situation, but similar motivation. I find it rather myopic to state categorically that a XXw20 is superior to a XXw30, even in engines that the OEM has recommended XXw20. Manuals and recommendations are not established by engineers, but by dweebs in cubicles that have other issues to consider beside the engine itself. And has been exposed somewhat by Brigadier's reference to the owners manual on his wife's car. This is hardly the first time I have seen different spec recommendations outside the U.S.
We are dealing somewhat with the same thing regarding the 20w vs 30w issue. Not exact same situation, but similar motivation. I find it rather myopic to state categorically that a XXw20 is superior to a XXw30, even in engines that the OEM has recommended XXw20. Manuals and recommendations are not established by engineers, but by dweebs in cubicles that have other issues to consider beside the engine itself. And has been exposed somewhat by Brigadier's reference to the owners manual on his wife's car. This is hardly the first time I have seen different spec recommendations outside the U.S.
