[JSeery]

Thanks Hoop, very informative! I looked up the temperatures used to establish the ratings, that is interesting as well (at least to me). The straight SAE viscosity is measured at 100 deg C (212 deg F). The W SAE viscosity is at various low temperatures. It would be interesting to see a viscosity curve between the low and high test points to see what the viscosities are at the temperature ranges that a flathead runs at.