First off new to the site, I've owned several fords and have always been a fan. Just purchased this 6.7 with 50k on it from a friend of mine and I choose it over a 6.4 I was looking at solely because of all the good mpg reviews. Truck is super clean and I bought it to work out of, I farm and most of my driving is similar to in town driving, truck will have about 1,500 ponds in the bed at all times " tool boxes, tools, air compressor". I drove it home 180 miles empty, about 14 mpg, I was expecting better, 16 or 17, I have a hard time believing the 20+mpg. Any way next two tanks yielded 11.6 and 11.7 mix of city and hwy. I bought a spartan tuner, egr, and dpf delete, also the truck had a air raid cold air intake when I bought it. That tank yielded 12mpg on 80hp tune all hand calculated at the pump although the lie o meter is pretty spot on. Anything else to ck the truck seems to run great. We have a 05 6.0 that gets 12.5 mpg with the same setup and driving, plus our old 7.3 we still have would get 15 to 16 when we used it, it's semi retired with 180k on it. Any input would be appreciated thanks in advance.

 

check the fuel filters and see if they need to be changed.

How fast were you driving when you brought it home? My DRW will get 16-17 empty so I think you should be able to get that as well.

 

My 2012 F350 CC SRW 6.7L gets 17-18 hand calculated empty and easy driving mixed city/hwy. Lately I have been putting my foot into it and average about 16.5 hand calculated.
Some say you'll get less MPG running winter blend. we'll see what happens in the summer.
On average I'm getting similar results as my old 7.3L truck.

 

I'll check the filters, if they were stopped up wouldn't there be a lack of power? I guess I don't understand why that would cause it to be worse? How would I know if they need to be changed? I change the others ever couple years and never noticed any change in performance.

I drove 75 on the way home, and I was pretty excited my other two diesels if you keep them under 2000 rpms they get better mileage. This one ran about 1800.

 

What gearing? 4x4? My '12 4x4 F250 with 3.73 gears averages 16 around town and some highway.

 

Sometimes it may just help. Another thing that may help is to do a relearn of the tranny. Try to disconnect both batteries. Then turn on the headlights for a few and make sure all the electrical is discharged. That should reset the learning process all over to your driving habits.

Since you are farming you will want to service by hours vs miles. Also be careful of the fuel requirements for this motor. You need clean fuel. No water.

 

^3.55 gearing?

 

I don't know the gearing, I'm guessing 3.55 based on the rpms at 75 compared to other peoples trucks. I looked around the rear diff but didn't see any numbers. My truck is a '12 4x4 CC SB 20" wheels with stock tire size no lift all stock as far as suspension and tires.

 

I don't have any problem with changing the fuel filter, can I use any name brand after market filter or do I have to go back with motorcraft filter?

As far as the trans it shifts nice and smooth I can do a relearn.

 

Well that helps us make sense. Those 20"s are what's getting you less then subpar mileage, or atleast a factor. I got 20+ all day on summer diesel with 18"s and 3.31s and going 65 on the highway. 75 cranks it down to 17.

 

Only OEM fuel and oil filters for the motor.

 

I have a 13 Platinum with 3.55 gears and 20s and I get 19 at 70mph. Got 23-24 at 55 flat land no wind. Average hovers around 15-16 when I'm not stepping on the throttle too hard.

 

I have a couple of friends that have 20's and one of them even has a 4" lift and they get between 16 and 18. I know I'm not gonna get 20 mpg but if I could get 14 or 15 I'd be pretty happy. I'll change the filters and let you guys know how it goes.

Does anyone know how to tell what gear ratio my truck has? Is there a stamp on the rear diff, or some other way to tell?

 

With 20" wheels, your truck can only have 3.55 gears. My guess is the load you are carrying is a big factor. If a 6.0 got about the same mileage with the same load, I wouldn't suspect anything to be wrong with the truck. My experience has been that the 6.7 gets slightly worse mileage than my 6.0 did with light to moderate loads.

With a mix of highway and local driving I can easily average better than 17 mpg, but in purely local, around town driving my mileage is more like 14. Purely highway I can approach 20 mpg. I have seen as low as 12.5 mpg with city type driving and that was with nothing more than a small box of tools and my fifth wheel hitch in the bed.

 

I think it should be on the door jam maybe?