It seems that one of the reasons newer vehicles have switched to 0w20 - 0w40 to help meet emission standards. I came across a bulletin from Toyota that mentioned emissions as a reason for the switch. I changed my Tundra over to Rotella T6 at 5k.
0w-40 won't do anything for emissions, it'll help with cold starting but it's still a 40wt oil. They did change the additive package around to help with emissions but a 40wt is still a 40wt.
