Originally Posted By: vinu_neuro
If you do a lot of short-trips VI might factor into fuel economy, but otherwise HTHS and friction modifier (surprise, oil chemistry matters!) are what really impact fuel consumption.
M1 0W-40 vs GC is a good comparison. Many have noted noticeable power loss and fuel economy with GC compared to other oils. There was also a dyno test from many years ago that compared various oils (at least 10 iirc), and GC did particularly bad especially since it had one of the lowest viscosities (HTHS and kinematic) in the group. M1 0W-40 had higher viscosity (kinematic and HTHS, 3.7 vs. 3.5), and it produced the most power out of all compared.
And note the VI difference between M1 0W-40 (188) and GC (166) which tells a big part of the story.
And large VI differences still make a difference at normal operating temp's. TGMO 0W-20 has a 216 VI vs something in the 150 range for a 5W-20. Even with the same VI TGMO will still be significantly lighter at normal operating temp's; hence better fuel economy even if cold starts are minimal.
If you do a lot of short-trips VI might factor into fuel economy, but otherwise HTHS and friction modifier (surprise, oil chemistry matters!) are what really impact fuel consumption.
M1 0W-40 vs GC is a good comparison. Many have noted noticeable power loss and fuel economy with GC compared to other oils. There was also a dyno test from many years ago that compared various oils (at least 10 iirc), and GC did particularly bad especially since it had one of the lowest viscosities (HTHS and kinematic) in the group. M1 0W-40 had higher viscosity (kinematic and HTHS, 3.7 vs. 3.5), and it produced the most power out of all compared.
And note the VI difference between M1 0W-40 (188) and GC (166) which tells a big part of the story.
And large VI differences still make a difference at normal operating temp's. TGMO 0W-20 has a 216 VI vs something in the 150 range for a 5W-20. Even with the same VI TGMO will still be significantly lighter at normal operating temp's; hence better fuel economy even if cold starts are minimal.
