So I have a question about how viscosities correlate to temperature ranges in real world use. I recently read that while a 0w40 meets pumpability requirements at the -35C to -40C range that outperform a 5w30, the 5w30 often has lower viscosity around 0C than the 0w40. I had thought that a 0W oil would outperform a 5w oil for cold flow at pretty much all temperatures below 40C. If that is not the case, is the common BITOG member recommendation of Mobil 1 0w40 in place of a 5w30 in many gasoline truck engines actually causing more engine wear on cold starts?
