Factors That Affect Fuel Economy: Fuels

Using fuels of a lower octane than the vehicle was calibrated to will cause increased knock sensor system activity. This will result in a net decrease in spark advance and thus poorer fuel economy. Using fuel of a higher octane than the vehicle was calibrated for will not increase fuel economy.

Variations in how much fuel is added to the fuel tank during re-fueling can greatly affect calculated fuel economy. These effects decrease as the distance traveled and the number of tank fill-ups increase.