Until recently the oil specified by Toyota was 5W-30. That's what my Tundra requires. However, when 0W-30 became common I switched to that (Mobil 1 Synthetic) and I did notice that 0W-40 was starting to be on the shelve. Now I see with the '12s that Toyota is specifying 0W-20. I'm curious why the 20. For those of us in areas where 100 degrees is common in the summer I would think that 0W-30 would be better. I asked my Toyota service manager and he, of course, wants to stick with the 0W-20 because that's what's in the book. I will use the 0W-20 until my free oil changes run out but when I start doing my own again I'll go to 0W-30 unless there's a really good reason not to. Does anyone have any thoughts or insight on this?