Here are the viscosity curves I was talking about. These are plotted as raw x/y data. which produces an exponential curve making it hard to see the entire picture in one plot.
In the first graph starting at -30C the 5W40 shows a significant improvement in viscosity at temps below-10C but above that temperature the viscosities become nearly indistinguishable. Regraphing the curve starting at 70C you can see the 5W40 actually has a slightly higher viscosity. as expected. As temperatures increase both oils continue to thin out and the curves get closer with the 5W40 remaining just a bit higher than the 10W30 all the way up to 170C
In other words the 5W40 viscosity is better at both extremes and nearly identical in the middle.
In the first graph starting at -30C the 5W40 shows a significant improvement in viscosity at temps below-10C but above that temperature the viscosities become nearly indistinguishable. Regraphing the curve starting at 70C you can see the 5W40 actually has a slightly higher viscosity. as expected. As temperatures increase both oils continue to thin out and the curves get closer with the 5W40 remaining just a bit higher than the 10W30 all the way up to 170C
In other words the 5W40 viscosity is better at both extremes and nearly identical in the middle.
