This was linked by
@Shannow a few years back:
In April of 2013, the Society of Automotive Engineers (SAE) introduced a new, low viscosity grade specification in revisions made to the J300 Engine Oil Classification. Formally labeled as SAE 16, the new oil specification will help OEMs meet increasingly strict corporate average fuel economy...
web.archive.org
To further contribute to higher fuel economy, a reduction in the oil’s high-temperature, high-shear (HTHS) viscosity limits has also been defined in SAE 16. Set at a minimum of 2.3 mPa⋅s at 150°C, this marks the first time ever that SAE has defined this limit below 2.6. Although it will help improve fuel efficiency throughout the entire oil drain interval, it opens the door for increased wear and tear on critical engine parts. This makes the development of new additives suitable for ultra-thin oils in high power density engines that much more critical.
GF-6B, on the other hand, forgoes the requirement to be backwards compatible with GF-5 applications and opens the door for the development of ultra-low viscosity lubricants (i.e., SAE 16) that will push the industry into areas of formulation that have never before been encountered. These lubricants will produce significant fuel economy benefits for many engine applications, but because of their low viscosity grade, there is the potential for wear or other durability related issues.
When asked about the implications that SAE XW-16 will have on passenger car motor oil (PCMO) performance requirements, Lubrizol’s PCMO Product Manager, Jon Vilardo, said:
“While it is generally accepted that lower viscosity brings an improvement in fuel economy performance, it can have a negative impact on durability; the protective oil film is less robust, or under the most extreme loading conditions, non-existent. In terms of performance requirements, this translates to a set of standards that will ensure fuel economy is improved via lower viscosity, but durability will not be compromised. The future proposed ultra-low viscosity GF-6B specification requires the same durability performance as the proposed GF-6A. This may require enhanced fortification of specific additive components or a different formulation shape to deliver the required durability in SAE XW-16 fluids.”
And some more quality content from
@Shannow:
Originally Posted By: Shannow * in fact I don't run 50s, full stop (unless you want to pick on the 40 blend in my sig as having 50 in it) Your sig is gone as of this writing; time to 'fess up to the SAE 50 in the sump.
bobistheoilguy.com
And another Shannow quote, with a link to a few papers:
...conditions being the norm for future engines? In a recent thread about high VI oils and VIIs few members mentioned that in the near future we will see more and more engines running in a mix of hydrodynamic and boundary conditions. I understand that even today's engine do run in boundary...
bobistheoilguy.com
Also a good point by Solarant that Shannow was responding to.
Lots of stuff on this in the bowels of this forum, though unfortunately most of Shannow's pictures are no longer with us, I was hoping to find the snapshot of the Honda paper that talked about "acceptable wear" that kicked off many of these discussions in the past.
From the top, DECADE old SAE-Lubrizol article...
" The future proposed ultra-low viscosity GF-6B specification requires the same durability performance as the proposed GF-6A. This may require
enhanced fortification of specific additive components or a
different formulation shape to deliver the required durability in SAE XW16 fluids. "
I use an outlier oil, HPL PP 0W8, which is beyond the realm of even GF-6B. Obviously, there is absolutely no data for me to stand on. The essential cutting edge strategies, declared above, are what I rely on for anticipated positive results with this oil. The good stuff is in my 0W8.
Thus far, my UOAs appear to be trending in a good direction. Innovative, outside the box base stocks, are not mentioned, as well as very stable, albeit expensive viscosity index improvers, and they play a vital role also.
Of course would not be possible for me to respond to skewering from phds, experts and highly informed posters in this situation. Even if I were a scientist, I literally would not know...yet.
In that greater durability is a requirement of these latest SP/GF-6 oils, it would seem that we can use 0W20 when it is spec'd, and with great confidence, in that there is adequate-good-make that excellent protection.