Check the link:
Specifically, I will refer to
Let’s assume, I use 0W20 at it’s rated minimal temperature of -30C, then I will need to find where 5W20 has to be no more viscous than 3250 cP to “meet the manufacturer spec at higher low temperature”.
Somewhere -20C or so, 5W20 will happily do no more than 3250 cP, so from the engine designed characteristics, it will provide the minimum flow recommended, at a higher lowest temperature threshold to compare to 0W20, then they become equivalent. The Amsoil comparison study I quoted above in the thread show that manufacturers routinely have the cold viscosity substantially lower than the maximum required by the spec, BTW.
The higher you go, the more you move out of the zone where lubrication might not be sufficient, but somewhere around -20C is the point from which it IS sufficient by the spec.
I’m not sure what exact threshold constitutes “the majority” for the US population, but here it some quite outdated map view:
For me it looks like quite a lot people would benefit from lesser oil evaporation rates versus the cold start performance they will never need, but it brings back the questions of “different specs for different climate zones”, “summer oil vs. winter oil”.
I will remind that I’m not questioning why Honda requirement is 0W20, as IMHO it is purely about logistics and cost of post-sales support. It is not about the technology.