Hey ya'll,
Help me figure this one out. 2005 F350 V10, 4wd, 4.10's, 45K miles. I live at about 5300ft. Since I bought the truck, MPG have been extremely consistent. As a matter of fact, I have never owned a vehicle that was this consistent. The F350 would consistently get a solid 9mpg (maybe +/- .02-.03/mpg). Fill up after fill up, I knew I would be getting 9mpg driving in town.

Last fall I got an SCT X3 from Mike/5-Star. Running the 87 tune thru fall and the entire winter, mileage increased to a steady 10mpg. Again, extremely consistent from tank to tank. MPG wasn't the reason I bought the truck or the tuner, but it was a pleasant surprise and a nice added benefit. Life is good, right? Well, come out of winter, I'm now getting a solid 11mpg in town. Over the last 3 tanks. Same driving habits, same routes, same gas station - nothing has changed but the season. So now I'm 2mpg over stock. How much better can life be? Heck at this rate, I'll be closing in on 20mpg by next summer! Ha! JK

So what's the deal? What would help mileage increase from winter into summer - all other things being constant?

 

I attempted to put this in my own words but decided to cut and paste was much simpler. Cars using summer-blend gasoline spew fewer harmful emissions and get slightly better fuel economy than those using winter-blend gas during the summer months.<O</O
The difference between conventional summer- and winter-blend gasoline has to do with the Reid Vapor Pressure of the fuel. RVP relates to the volatility of a gasoline. The more volatile a gasoline, the more likely it will evaporate as the temperatures rises; evaporated gasoline contributes to unhealthy ozone and smog levels. Summer gasoline has a low RVP and is less likely to evaporate when compared to the high RVP winter grade. The Environmental Protection Agency says conventional summer-blend gasoline contains 1.7 percent more energy than winter-blend gas, which contributes to the summer blend’s slightly better gas mileage.<O</O
The Energy Information Administration says the switch between the two fuels happens twice a year, once in the fall (winter blend) and again in the spring (summer blend). Summer-blend gasoline is typically more expensive to produce than the winter blend, and it won’t affect vehicle performance or the durability of the engine and fuel system, according to the EPA.<O</O
In many large cities as well as <?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-com</st1:State>California and <ST1New England</ST1, the EPA requires the use of reformulated summer- and winter-blend gasolines. These RFGs contain oxygenates that lower RVP and other toxic chemicals even further than conventional gasoline.<O</O

 

Yup. What he said!
Other possibilities:
The percentage of alcohol in the fuel decreased a bit.
Your station normally pumps reformulated / high oxygenate fuels and this time didn't.

Bottom line: Just because you always buy from same station doesn't mean you always get the same fuel! Enjoy it while it lasts, I'll bet it drops again next winter.

 

Yep, its the blend.

 

Be happy!!!!

New York State gasoline where I live will give me, year 'round, 9.8 to 10.3 if I use a light foot. If I take the truck to PA or VA it will go to 11.9 to 12.3. Even a couple of past F150's showed those kinds of differences.

 

Are you sure your friends or neighbors aren't adding a few gallons of gas when you're not looking. It's been done before, but not at these prices.