It is true that winter fuel doesn't pack as much energy as the summer fuel.
However, there are other reasons for lower fuel economy. Colder ambient temperature places a greater demand on the engine's cooling system. The cold temperatures causes the engine to consume more fuel to maintain the operating temperature. Using the heater also cools the operating temperature.
Low tire pressure, dragging brakes, out-of-alignment, air condition (defogger uses the air conditioner to reduce moisture inside vehicle), a weak or coated mass air flow sensor will give inaccurate reading to vehicle's computer.
It looks like you've maintained your vehicle well so I wouldn't suspect that there is an issue. Unless this continues into spring.
Hope this answers you question.
Monday, January 20th, 2014 AT 7:40 PM