[1] API FA-4 10W-30 has the lowest High Temperature High Shear (HTHS) value and hence characteristically better fuel economy. With this in mind and through analysis of industry data available online, fuel economy improvements have been calculated relative to an API CK-4 15W-40 engine oil and in combination with a synthetic 75W-90 (relative to an 80W-140) gear oil.
[2] Using industry supporting materials found online and in print, fuel economy has been calculated and shows improvement relative to an API CK-4 15W-40 engine oil and in combination with a synthetic 75W-90 (relative to an 80W-140) gear oil. It also takes into consideration the inherent benefits of using a lower High Temperature High Shear (HTHS) oil as shown in the new API CK-4 platform versus CJ-4. Please also note that a 5W grade will be better in cold temperature applications than a 10W, so while not better at fuel economy, it will work better in different climates. Actual results are dependent on external factors including, but not limited to: driving terrain, weather conditions, tire pressure and severity of operating conditions.