Fuel Mileage

[richfaa]

There seems to be a wider range of MPG towing vs not towing with a diesel..why is that????

[Dave e Victoria]

Rich,
I am not surprised that we see a wider spread in MPG loaded than empty. There are a lot more independent variables once you hook up to a trailer as well as a lot more effect from variables already in place. I suspect towing speed is biggest difference. Empty, I see little difference between 55 an 75 MPH. Hooked up, it is a different story I see 2 or three MPG difference between 55 and 75 with the trailer on.

Prevailing winds have a bigger effect when hooked up than empty. For instance, on specific runs I can get any where from 9 to 13 MPG just by varying headwind at a constant 65 MPH.

The next effect is weight. In this reporting population, you have trailer weight that varies from 10,000 near empty for smaller trailers all the way up to 17,000 for a fully loaded Cambridge. I've never seen a specific weight analysis for MPG effects but it stands to reason that it has to be there. Even the energy that is wasted in the brakes for a large load must be accounted for.

Finally there is terrain. The fact of the matter is we spend far more time going up hills at 3 or 4 mpg than going down at 40 mpg.

To sum up, The pull from Amarillo TX into Albuquerque NM with a fully loaded trailer and a 45 mph wind directly out of the west will destroy anyone's average. Any one of us who does that very often is going to suffer at the pump. (BTW, 70% of the time on the return trip the wind will have switched -- that's just the way it is.)
Dave

[sreigle]

Dave, we had the same kind of headwind you mention, between Amarillo and Albuquerque and also between Albuquerque and Flagstaff. However, we were eastbound with the wind also from the east. Just lucky, I guess.

[Lstierw]

We left Washington State the middle of October and have averaged pretty much 15 empty and 10 pulling.

[PowellsMonty]

I bought my F-250, 7.3, automatic used and the previous owner put larger tires on it thjan what came from the factory, they do look better. I am wondering if that would affect fuel mileage. I get 12 around town and 16 Hwy. We live in Western North Carolina so it is mountainous. Got 18 on flatland, but get nowhere near what most owners are claiming to get.
Thanks.

[Charlie]

Mike-
Sounds like your mileage might be a little lower than mine, but not much. However the town number does seem rather low, but you are running a 4x4 and your truck weight is greater than mine.

I have a 2001 F-250 7.3L 4x2 with LT265/75R-16 (factory spec) tires and the rear end gear ratio is a 3.73. I have tracked mileage with a computer program that I set up from the day I bought the truck and up to date it gets 17.962 MPG without a load. I have under certain conditions had tanks that yielded as much as 21 MPG, but these are far and few between with conditions at freeway speeds, not much stopping and maybe with a tail wind. I also installed a 80 HP performance chip in the computer that showed an improvement in mileage after installation. I don't do much town driving as I live in the country and 95% of my driving will be on a highway. There is an advantage to living in Texas....for the most part it is flat.

Pulling the Monty also depends upon conditions but usually around 10-12 MPG.

If your over sized tires are not giving you the mileage you think you should be getting one thing to consider is that the odometer reading will not be accurate. If you have a GPS, plug it in and leave it running until you use up a tank and use the odometer on the GPS to figure your mileage. The GPS will also give you a truer reading on your speed.

[Searchers]

Mike,
I've done as Charlie recommends with the GPS unit with much more accurate results. I'll also mention that larger diameter tires will have the same effect as running a higer (numerically smaller) rear end gear ratio. Besides throwing off the odometer reading you may be running the engine at certain speeds below or above peak torque curve using more fuel. I have a 1995 7.3 with a 4.10 ratio and find I get the best fuel mileage by maintaining the engine speed at peak torque, which is 2000-2200 rpm. The torque specification may be listed on a valve cover label on your rig, as it was on mine.

[PowellsMonty]

Thank you for the advise!