There is always a discussion about expected fuel mileage, when a particular brand and size of motor is mentioned. Predictably, you will get several replies that don't match. There are many variables that determine what your fuel mileage will be, and how it will probably differ, from others who own the same motor.

Equipment: The same motor can be installed in trucks that will vary, with different installed equipment. A Ford diesel can be installed in a 250 or 450. The trucks weigh different amounts, they will have different rear axle ratios, some will be SRW while others are DRW, 2 WD and 4 WD. Some will have small mirrors and flush bed sides, others will have large towing mirrors and extended fenders. The installed tires, tire pressures and numbers, will determine the rolling resistance, from a heavy cleated mud and snow, to a smoother all weather variant. The transmissions will vary between automatics and manual. Each one of these differences will effect the fuel mileage.

The trailer that is being towed will also vary: It's weight will be a major factor along with its size. A 7 1/2' or 8' high trailer has more wind resistance than a shorter one. A wider 8' trailer has more surface area the a narrower 7' trailer. The shape of the nose, will determine how aerodynamically efficient its design will effect drag. If it has an air conditioner or a hay rack and its attached ladder, can contribute to parasitic drag and fuel mileage losses. Running with the drop down windows open, causes more drag than when they're closed. How much of a load is being carried, how many axles are installed, how well balanced the load is between the truck and trailer, will all vary the final fuel mileage.

The maintenance will effect mileage. Higher tire pressures reduce rolling resistance. Synthetic fluids reduce friction and improve mileage. Dirty filters reduce performance. Fuel additives can be advantageous. The type and quality of your local fuel can vary from area to area. The elevation at where you live, will effect the available power from your motor.

Driving habits are a major contributor to variances in mileage. Hard braking and acceleration will lower the figures; the speed at which you travel will greatly determine the resulting mileage. The topography in which you drive, will directly effect how the motor is working; hills or level, straight or curves, open spaces or starting and stopping. The trucks may be traveling open interstates, or running across town to a local 4 H meeting.

There are many variances that effect fuel mileage. It is NOT realistic to expect all owners of a particular motor, to experience the same performance and mileage. Because one owner of a 6.7 Dodge can pull a 15K # trailer and get 14 - 15 MPG, doesn't mean all the owners will be able to duplicate those figures. Some owners will experience more, some with less mileage.

Gard

Wonder how much better mileage this new 6.7 will get over the old 6.4 powerstroke...?

 Ford-designed 6.7-liter turbo-diesel V8 producing 390 hp and a pavement pummeling 735 lb-ft of twist (at 1,600 rpm).

http://www.autoblog.com/2010/02/25/2011-ford-super-duty-power-towing-specs-released/#comments

From what I seen from the engineers discussing this, The mileage should be about 2 mpg better than the 6.0L, which was already a couple of mpg better than the 6.4L

As gard mentioned in his post.  There are so many variables that affect fuel mileage.  I know I see my truck go from 10.5 to 21 just depending on the season, winter fuel vs summer fue, outside air temps, city vs hiway, what trailer I am towing, etc

I'm excited to see the new Fords show up.  But they have gone past the point of me being able to buy a new one any more. I paid $40,000 for my King Ranch in 2006, My sister just ordered a 2011 King Ranch for $56,000.  That's a 40% price increase over a 4 year period. And during that same 4 years my income has decreased because of this lousy economy.

.....and fill it from the same pump, using the same fuel filler nozzle, do this three times and get a hand calculated average.