Fuel Economy I get only 11MPG after Spark plug change

[Jolly Roger VX'er]

All my vehicles have always shown better mileage in the summer, although some decreased a little when it got hot-hot (>90*F) out.

yep..this is what I was trying to say earlier


My other vehicles with exception of the VX always followed this trend of starting to get worse mileage as it got hot-hot (>90*F). I found it puzzling when my VX would jump alot higher (better mpg) as the temps soared,,,,,bring on global warming...lol.

[VehiGAZ]

PS - not all states have different fuel grades summer vs. winter. Some switch to a lower vapor pressure grade in the summer to reduce gas evaporation - a huge contributor to smog.