Here is nearly 8,000 miles worth of data from my truck before I traded it. It was a 2011 with 3.55s. If I had to do it all over again I would have gotten 3.31s, even when towing heavy the 3.31 trucks do a great job, and they seem to get 1-2 MPG better when unloaded.

Truck (Ford F-350 Super Duty) | Fuelly

 

Yea but, the tire/wheel combo look so small on along truck. The 2os look so much more proprtional to the truck.

 

PH, agree....
is it because when we first get our trucks we are 'gentle' with the new toy and drive easily until we figure it out and
THEN it's just an appliance that we run hard !

So it averages out...
good mpg at first when easy,
then even though the mpg improves a bit over time, we are driving it harder and so the mpg staying the same is ok IMHO !

 

Thats not why my milage has dropped. Everyone thinks I am the slowest driver they know. It seems the more power Ihave the more conserrvative I drive. Ive lost about 3 mpg. There is something else going on. I started out at about 20.5 mpg and now at 75oo miles about 17.5 mpg. I also dont idle but it says about 25% idle hours.This milage is about the same as my 150000 mile 6.0.... Same driving......I even use my graph mode to keep it in the sweet spot.

 

Its not that it matters that much, its just the game of it. It seems in 2012 with all the crap we have to put up with on these trucks, all the computers and tech they should do a lot better. My test drive did 20.5 and started out and ended in town.

 

I'm doing about 15 or so in town and average 21 on the highway up and down hills in my 12' F250 PSD. This a vast improvement over my previous ride, so I'm not complaining too much. I would be concernded too if mileage suddenly dropped 3MPG though!

 

Well I have the 20inch kr rims and tires stock the trailer was a flat bed with a hummer on it. My 2006 F250 Harley with 20 inch rims got better fuel mileage when not towing like 21-23 and towing like 10 so i guess it kinda of equals out except i am not blowing egr coolers all the time lol I love the 6.7 so far though

 

17.5 average mpg unloaded with a fiberglass cap. 20" tires and 3.55 gears.
20kmi on the odometer. My 2008 6.4 got about 12 mpg at it's best driving the same.

 

well see how it does next month towing both ways same distance with 36s toyo open countrys and sct tuner and no cali emisions Guiness beer only lol and 4000 miles under her

 

I have a '12 with 3:55 gearing and get about the same mileage but most of my daily driving is to and from the office and consists of some city but mostly interstate at speeds up to 75. So Monday-Friday I average between 17-18 mpg.

I also find that with highway mileage while not towing, mpg varies depending on the prevailing wind - going into the wind mpg drops considerably - for obvious reasons.

I hate when it goes into regen, seeing mpg drop,but try to mentally compensate this because it truly is better for the environment - I like the fact that I do not have smoky exhaust like early generation diesels do.

 

Yeah you're not kidding, that head makes a huge difference! The front of this thing is like a big sail! But for having 800ft-lbs the MPG's are pretty amazing! So I am still a bit unsure, are the 3:31 guys doing a whole lot better? I was thinking about going that route.

 

If I had it to do over again, I would go the 3.31 route then add aftermarket 20" wheels with decent tires. The 20" wheel and tire package is overpriced and the tires are horrible. With the difference in tire size, the final ratio is about the same between the 3.31 and 3.55 packages, but adding a taller tire to a 3.31 geared truck will help put the rpm closer to where they need to be in 6th gear.

Every gear in my truck is too low. The 6th gear OD should be more like a 0.62 with all the torque that these trucks have. Most of the difference in all the magazine tests where GM outshines the 6.7 is due to Ford's poor choice of transmission ratios.

 

I have an '11 with 3.55 and 20" wheels. Just made a 2600+ mile trip, no towing but had family of four packed up and bed was full with everything including kitchen sink. Overall mileage was 18.2 including highway and city (Chicago) driving. I was hoping to get 20 mpg total for the trip though.

 

I picked up a 2011 with the 3.31 and 18" in Kansas and drove it out to Utah for a Friend and I've driven my truck with the 3.55 and 20" enough.

Both trucks get 18-18.5 mpg on the interstate at 80 mph. So I didn't see any improvment in mileage for the 3.31/18" over the 3.55/20"

My 6.7L towing doesn't do much better mileage wize than my 2006 6.0L did. But empty the 6.7L does better.