20 Weight Oils and Bearing Design
I have a new Toyota Tacoma with the 4 cyl and the only oil recommended for it by Toyota is full synthetic 0W-20. I've read several sources that claim the move to 20 weight oils is largely an effort to eek out a tiny bit more fuel efficiency. I know years ago Ford (and I think Honda) changed, over night, the viscosity recommendation of several of their engines from 30 weight to 20 weight. To the best of my knowledge they did not change the bearing design when they did so. This seems to defy logic as the engineers would have designed the bearings and loadings with a certain viscosity in mind and a thinner oil would accelerate wear. My question is are the manufacturers simply trading slightly increased fuel economy for an increase in engine wear or are the bearings designed with the decreased viscosity of 20 weight oils in mind?