has anybody in maryland or the northeastern united states seen thier milage drop when they went to the winter blended fuels ? i thought it might be the gulf gas ( all chevrons and texaco's in maryland were sold and are all going into different brands ( gulf , mobil, ect , but i switched back to citgo and the mileage has not improved . any ideas or thoughts ??
I think that there should be an increase in mileage if you switch to winter blends since it has a higher gas % and lower ethanol % which performs better in winter no? This is really an issue with starting cars using E85, but I don't know that it is with E15. Maybe fuel economy issues are more pronounced in cold weather with E15 vs. warm weather.
Winter gas blends use more of the cheaper, more volatile hydrocarbons like butane that burn better when cold but also contain less chemical energy. This is why there is a slight drop in price and mileage that occurs when they switch to the winter blend. The purpose of different winter and summer blends is primarily for evaporative emissions; summer gases must use the less volatile, more expensive blends which don't evaporate as quickly in the warmer weather.
This has also been consistent with my experience. Over 138 tanks in our Scion it is pretty easy to pick out the exact first tank when the gas stations switch from summer to winter gas and vice versa. Our average over 26 tanks this summer was 31.3 miles per gallon, and in 10 tanks since the end of September our average has been 28.2 miles per gallon, about 10% less. From May until October we only had one tank below 30mpg, and since then we've only had one tank above 29mpg.
All brands make the switch. It is required on May 1st and September 15th every year, but I think sometimes the switch can be made earlier.
More Butane is in gasoline in the winter to increase vapor pressure. Gasoline needs to be more volatile (higher vapor pressure) in the winter so engines will start easily. A high vapor pressure fuel in the summer months can cause vapor lock and other problems. Vapor pressure is NOT suddenly changed. It is phased up starting in fall and phased down starting in spring. The vapor pressure regulations also can be different for different locations in the US due to differences in climate extremes. This has NOTHING to do with the amount of ethanol added to gasoline. I have personally hauled many loads of butane to a nearby refinery in winter and have hauled butane to storage in the summer.