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Winter vs summer gas--mileage

They switch gas formulas soon in my area.

Which formulation gives better mileage?

I would guess summer, but that’s only a guess.

People usually report lower fuel mileage with the winter blends.

Government Fuel Economy Link:


I notice a ~10% drop in mileage in the winter. For instance my 2000 Blazer mpg is 16.5 in the winter and ~18 in the summer. My 2010 Cobalt under the same conditions get ~27 winter and 30 mpg in the summer. S. Jersey uses E10 year round, I’m not sure of the differences between the summer and winter blends.

Note: MPG is calculated every third or fourth fill-up (~1k interval).

Ed B.