It's complicated and a lot of folks don't have a complete understanding what exactly those SAE number really mean.
Encoded in those numbers are variables like Low Temperature Cranking Viscosity, Low Temperature Pumping Viscosity, Low Shear Rate Kinematic Viscosity (at 100 C max.), and High Shear Rate Viscosity (at 150 C min.)
On top of that, you have different shear rates at different parts of the engine.
Also the viscosity is dictated by your bearing clearances, in relation to you oil temperature.
Let's say you have a clearance of .0034-.0039 on your mains, under 160F oil temperature you are fine with a 10W-40.
If you temp is over 220F, you need a 20W-60.
Also the tighter your clearance , the thinner your oil needs to be.
Personally I stick with the original manufacturer viscosity, especially since I don't drive in the winter, when there is tons of salt on the roads.
So my cold start temperatures are usually just around 60F and up anyway.
Last edited by Stovebold6; 09/03/2023 6:36 AM.
