I have it on good authority that the NHRA Top Fuel dragsters are slowly transitioning from the tried-and-true SAE 70 to the much more fuel efficient 0W-70 now offered by Lucas. (this is parody folks)
Yes, the lower operational viscosity during warm-up probably results in a slight improvement in MPG. The differences are most significant under 5C, so I guess it depends how long it takes for your engine oil to reach 40C. In my mild climate, my engine oil goes from 60-70F to 100F in a few minutes of driving. For someone in a cold climate, during winter time, I imagine this to take much longer.0W20 is almost always synthetic, & 5W20 can be either blend or full syn. I'm sure there's a microscopic MPG improvement cold, too.
Whats it like at -30C? Seems to be pretty differentiated at 0C which is only just freezing. Half of the country freezes pretty good in the winter. Here in South Carolina looks like it probably wouldn't matter much, but as already said its easier to say the same thing everywhere.Yes, the lower operational viscosity during warm-up probably results in a slight improvement in MPG. The differences are most significant under 5C, so I guess it depends how long it takes for your engine oil to reach 40C. In my mild climate, my engine oil goes from 60-70F to 100F in a few minutes of driving. For someone in a cold climate, during winter time, I imagine this to take much longer.
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I would guess that at 0F, both grades (in synthetic) will flow just fine, but the lower viscosity of the 0W20 will result in a measurable improvement in MPG. That is probably why the OEM's recommend 0W-20 over 5W-20 for a one-size-fits-all recommendation.Whats it like at -30C? Seems to be pretty differentiated at 0C which is only just freezing. Half of the country freezes pretty good in the winter. Here in South Carolina looks like it probably wouldn't matter much, but as already said its easier to say the same thing everywhere.