We used to tow a decent sized boat with a 1976 Elderodo. With a 3speed auto and 500+ cubes you can imagine the gas mileage lol. I don't get it why they can't / won't make it more accurate and overestimate by 1.0/+/- MPG. I am on my 4th tank now. It appears the issue is with the remains fuel capacity. Anyways, I started running Shell top tier and it's bottom better as I got 19.0 last tank. Readout said 20 which is were I would like to be. May pick up a little with Mobil 1 ect.

 

I just passed 5000 miles on my '15 F-150 5.0 coyote, 4x4 with 3.55 gears, and 36 gal fuel tank.

I drive about 40 miles a day for work, some freeway and mostly winding back roads. I have been on a few 350+ mile trips for hunting (minimal elevation change) and snowboarding (8k foot elevation change). Some driving has been done in 4 wheel, but large majority in 2 wheel.

My lifetime mileage has been almost exactly 18 mpg, and I often get low to mid 20's on the freeway traveling between 65 and 75 mph.

There have been no mods made to the powertrain, and she rides on OE wheel and tires, (275/55/20) Hankooks. I do have a bed cover, but don't know if that would make a difference.

I expect if I excluded the first thousand or so miles for the break in period my numbers for mileage would be a little different also.

 

On my second tank of no ethanol gas right now. This thing is definitely not as snappy off the line and I don't feel like I have as much power versus 87 or 93 regular.

 

Does going with a larger diameter tire give better gas mileage? I'm thinking if the tires turn slower due to a larger tire then the rear end turns slower therefore making the engine turn less RPM's. Am I looking at this correctly?

I have the 5.4 with 3:55 rear. The tires on mine currently are LT265/75R16 which are 31" in diameter. Stock size for my truck are either LT245/75R16 at 30.5" diameter or P255/70R16 at 30" diameter.

 

Not usually. Larger diameter tire = heavier tire (in the general case) plus it makes the differentials have to work harder.

 

You have a 5.7 what? Ford didn't make a 5.7. What year and how much tire are you adding?

 

5.7 is I think Toyota

 

I corrected the typo from 5.7 to 5.4. Its a 2000 F150 4x4.

 

You will gain hwy mpg up to a 265/75r16 on flat ground but city mileage will suffer some. Anything taller or heavier than a 32" D load rated tire and you will see a drop all around.

 

Thanks, most of my driving is on rural country roads.