Originally Posted by hallstevenson
An automaker will be very unlikely to make a blanket switch from one oil weight to another without knowing the risks (if any). If they gain fuel economy with no impact on engine wear, it's a no-brainer. Plus, the fact is with Honda, they back-spec'd the oil change almost as far back as 2003 or so (in fact, 2001, with the Civics) to say 0W-20 is acceptable. They get ZERO benefit from CAFE regulations on prior year models if I'm not mistaken. Does their dealer network benefit by being able to buy more 0W-20 vs a mix, sure they do, but Honda of America has no obligation there as dealers are privately-owned, not corporate-owned.
FWIW, with Honda's 3.5L V6, they went back to 2002 with the Odyssey and 2003 with the Pilot switching from 5W-20 to 0W-20. You have to back to prior years where Honda spec'd 5W-30.
They switched to 0W20 bcs. there is some benefit in cold cranking pumpability in certain areas. Why confusing consumers with: if you live here use 5W20 and if you live here use 0W20, when both oils provide same MPG numbers. There is no difference in CAFE moving from 5W20 to 0W20. However, there is moving from XW30 to XW20.
Moving older models to different grade can mitigate some known issues. BMW retroactively moved some engines on the US market to lighter oils as experience showed that due to driving regime in the US among BMW drivers, some issues on V8 engines could be mitigated using lighter oils.