Winter fuel measuring 38 API gravity (lower energy/lower BTU content) is responsible for another 2.5% fuel mileage penalty.

The total AVERAGE MID WEST WINTER TIME (25°F/-4°C) penalty on fuel economy amounts to 15.5% (13% temperature + 2.5% winter fuel) or approximately 0.9 mpg. At 0°F (-19°C), the fuel penalty approaches 1.1 mpg.

Winter fuel with higher API gravity will generate a higher fuel mileage penalty. In the southern region of Canada, 41 API fuel translates into a 5% fuel mileage penalty (0.3 mpg). Further north, kerosene with 48 API gravity results in a 15% fuel mileage penalty (0.9 mpg).