Source? My understanding is the 0W-40 recommendation is only for a certain batch of engines that was recalled. Current 2026MY still specifies 0W-20.
https://contentdelivery.ext.gm.com/..._Denali_OM_en_US_U_19431985C_2026JUN08_3P.pdf
It's a risk vs. reward type of thing. And it's the same gamble for the consumer as it is for the manufacturer. The goal for the manufacturer was to use the thinnest oil possible, for the best fuel economy, to gain the most $CAFE$ credits. Period. That's it. Otherwise this whole oil game never would have started.
But at the same time have the engine live past the warranty period. It's quite apparent they either have reached that limit, or else, (in the case of the GM 6.2L), have passed it.
Hence the factory recommendation to walk back thin oil, and increase viscosity after all the expensive failures they've had to deal with. Because let's face it, they sure as hell didn't go to thicker oil to make matters worse.
Toyota has always said right in their owners manuals, through this whole thin oil game, that a heavier viscosity may be a better choice if the vehicle is operated under "severe" conditions. They're very careful with the wording so as not to use, "recommend"..... Again because of CAFE.
Other nonsense in the Toyota owner's manual states that if 0W-16 oil is not available, 0W-20 can be used.... But must be switched back to 0W-16 at the next oil change.... Or else what?
In one sentence they tell you that a higher viscosity "may be" a better choice. Then in the next paragraph they tell you if you use it, you have to switch back at the next oil change..... Or else what?
This has all become a big, contradicting word game, so as not to upset CAFE, but still "suggest" that these water thin oils may not be the best choice over the long haul. Then naturally the whole "thinner is better" crowd all feed off this like starving cattle.
And let's face it. with the GM 6.2L V8, you can argue all day long if it's a good or bad engine design. But again, GM didn't go to a higher viscosity oil because they thought it would be a worse choice.
In hot weather the
only positive with these ultra thin oils, is an almost unmeasurable fuel mileage increase for the average consumer....... At the expense of the very possible reality of shorter engine life...... Even though someone always seems to know someone's buddies girlfriends cousin, who's engine lasted X number of miles on it.