I have a 3.31 which should get better mpg??? I typically tow at 70 mph. Yesterday I towed about 565 miles and averaged 7.4 mpg. All time worst. But I had a 30 to 40 mph headwind 80% of the drive. THe worst segment was slightly uphill for 100+ miles, 35+ mpf headwind.....6.4 mpg at 70 mph.

I can't lock out 10th all the time. when you have a steep incline and want to maintain 70, 10th will not do it. 8th is needed.

Interesting. Have you compared your RPM to the Engine performance curve. You may be driving on the bottom edge. I am with you on the 70 mph as I did the same. My 04 6.0 got the same mileage you are seeing (6 to 8 mpg) but it was very near flat out holding that speed. and that was with 4:10 gearing. Maybe try a lazy day at 65 and see what happens.

I am slowly learning to go a bit slower, and shorter days - but I hear you when I got to get there.

Keith

Not a bad idea.

I have a Banks iDash that helps know what's going on (shows me EGT temp, regen %, and much, much more). When ECU HP is above 300 and boost is over 25 psi, I know the mpg is going to suffer.

Slower and shorter days doesn't work for me

Thought I would check back in after towing partway across the country (MD to CO, NM, TX, AK) and the East Coast (MD to FL).

On our trip last summer, hand-calculated towing:
flats going 65mph - lowest was 9.5mpg and best was 11.7mpg. Mountains I was right at 10mpg. Going to FL and back I was averaging 10.8 mpg towing and 18.5 mpg solo.

The truck has 15K miles on it now. Solo it hangs at 18.7mpg (includes some around- town driving. On the highway it appears to get over 20mpg according to the truck's readout (but my trips are not just highway ....)

Towing to Assateague and back (MD) - flat and 55mph roads I got 12.6mpg average (one fill-up was 13.1mpg that included some solo driving) .

You have to factor in DEF though - I fill up with DEF every few fill-ups when towing because I use a lot of DEF towing.

The truck likes to work - towing the Rockies I had no issues climbing I70 to the Eisenhower Tunnel (over 10K feet) and then through the Rockies - kept the posted speed limit with plenty of gas pedal to spare. My last truck (2005 Duramax) towing a 40' (but much lighter) 5th wheel was floored going up I70 to the Eisenhower Tunnel - and the temperature reached over 240 degrees. The 2020 F350 had no issues ever with temperature - only heard the fan clutch kick in twice the whole trip and temps never went above 220. Tranny runs a tad warmer but that is normal.

Thanks
Looks like I am going to like my 3.55 gear choice.
Keith

howson Cate&Rob Yoda I run an app by the name of https://www.fuelly.com/ for mileage monitoring.

Basically you input the current mileage, the cost per gallon, and the gallons. It then calculates the total fill up cost, the trip mileage (checks) and allows for notes. I add notes when I tow the trailer. you can even put in the fuel station by use of GPS and internet connection.

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This would be the trip from Home to Pigeon Forge and back with mixed towing.

'21 F350, 6.7L, 4WD, 6.75' Box, SRW, 3.31 rear end. Pulling Momentum 381M with 2K of motorcycles in the garage: total weight north of 18K#. Solo runs 19 - 20 mpg, dependent on speed; the first 1K miles was 20.5 mpg highway cruising @ 75 mph. Depending on wind and grade, pulling is 8 - 10 mpg @ 67 mph. Can't compare directly to big gasser, but I'm really impressed with the diesel's power.

I'd rather have had a 3.55 rear end but with supply chain issues last summer I couldn't find one at a reasonable price.

I'm curious if 5th wheel towing gets better MGP than bumper towing (particularly taller, wider toy hauler travel trailers). Would be interesting to determine the drag coefficient to both....

I didn't see much MPG difference when I went from a TT (10K lbs) to a 5th (currently 14.5K lbs), but seat of the pants, the 5th pulls easier. My truck has enough power that both trailers are not much effort for the diesel engine, and although it is hard to quantify, for me, the truck and trailer combo finds a happy cruising speed, and the 5th is about 5 mph faster.

Looking at both, the 5th would have the turbulent air from the truck only hitting the upper portion, and to a small extent the lower behind the tailgate area. The TT would have all the turbulent air hitting most, if not all the frontal area of the TT. Although not well know, or paid attention to, the Fords have a frontal area restriction for towing.

Thanks. That's my theory, much more turbulent air with a TT vs a 5th wheel. I think drag plays a bigger role in mpg than weight

Yes, and add that on both, which should be equal, the sides, roof, and rear, all play a part also. The sides have a good amount of drag, roof with the a/c and vents, and the rear of the trailer with the air going everywhere behind the trailer.

An interesting thing on turbulence and how it affects the rear. One of the helicopters I use to fly, the tail had a rounded cone on the end of it, with the engineers believing that it would provide better aerodynamics. They developed a larger version of it, and while testing it, they did not have the rounded cone on it, just a flat surface. When they put the rounded cone on it, they found out that it was less stable, with more yaw motion. They ended up leaving the rounded cone off in favor of the flat surface for the final version.

Yoda Keith, Please download the app, create an account and track your mileage. www.fuelly.com I've been doing it since new on the 18. You will be amazed at what you can learn.

LOL
Joseph
I will give it a try, but got news its taking 6 weeks min for shipping. Truck is still in production - past expected time. However you need to know I am not smart phone savvy.

The app looks interesting,

Thanks for the link. I hope it helps others too.

Fingers crossed on it getting to me by the end of April. At least I wont need to worry about snow - well maybe
Keith

Keith, you can also input on the computer. I use the phone while pumping fuel so I don't have to write the mileage on the receipt and not loose it. Its 3 inputs, then add fuel up at bottom of screen and verify input 4 is optional and that is for station. Input 1 is current mileage, input 2 cost per gallon, Input 3 gallons pumped. Once you put in the gallons, it populates the cost value before adding as the first check of data.

Does it help you figure out how to operate the pumps?????



Just kidding
On my Georgia trip I pulled into the truck lane at a new station and had to get help. Pump kept asking a lot of dumb questions I did not understand and I could not find the override button. The attendant laughed and reset it for my credit card only. He did admit it was set up for Professional CDL Drivers and that it was confusing for us RV folks. He actually was a nice guy and programed in a discount for me at the end. I cant remember where it was at, but the BBQ sandwiches were to die for.

Keith