My humble theory on 0W40 is really based on the fact that maybe 80% of wear on the engine moving parts is due to lack of lubrication at start up. Considering the length of time that our cars sit between startups, the faster (due to lower "0" viscosity when cold) the
oil gets to these mating surfaces, the healthier it is for the engine. I installed a 3 quart Accusump to aid in startup pre-lubrication as well.
Additionally, I think it was Bob in Ct that came upon a test article that M1 0W40 actually is thicker under operating temps than M1 15W50. Go figure...
