Two fifth wheel towing scenarios...

If you're concerned about fuel mileage I'd stay away from the Ford 6.4.
There are way to many variable to give a good answer to your questions.
I agree with donn, between 5 and 15.

Impulse, what in the world diesel are you comparing to? I have an '05 Duramax that hauls and tows over the ratings often. I've never gotten less than 10 mpg. Most of the time it's around 15. I couldn't get 9 MPG if I tried.

stickdog wrote:
The 6.4 is not noted for fuel efficiency. The 350 would have 3.73 diff and the 450 would be 4.30. I'm pulling 15,000 with TV in sig and would be happy if I averaged 9 mpg. I do feel there is a difference in fuel quality which also affects mpg besides the wind smoothness of the road and terrain.
There is also the problem with fuel availability as the 6.4 is only cleared for 5% bio and in some areas the fuel stations all have up to 20% bio stickers on their pumps.
I would love to trade my 09 6.4 for the newer 6.7 just to avoid problems with bio-fuel.
I have had 10 mpg on occasion flat ground good road and 55 mph, hasn't happened too often.

your dually has the 4.11 gears, right? my 08 4x2 did. best I saw towing was 9mpg. I have since upgraded to a 2012 dually ford 6.7, with 3.73 gears and get 10mpg towing my 15k fw. and between 15 and 17 empty on the highway.

I would guess the OP would get 8-9mpg in either scenario.

Impulse24 wrote:
I have a 1996 GMC K3500 SLE with a 7.4 (454) and a 4.10 rear end.
Prior to buying a 5th wheel, We spent hours researching for the best tow vehicle and best fuel economy available. As usual I was told Oh buy Diesel, It will give you the power for climbing. That is true but overall if you have a Diesel it costs you more in Fuel purchase and repairs. I have also read the Myth Busters report that Wings and other type of deflectors don't work.
We'll I beg to differ about Diesel is better and air deflectors don't work. I average 10.2 mpg using 87 octane gas and a Wing adjusted to push the air over the trailer. Prior to using the wing I averaged 8.5 mpg my average speed is 55. So I prefer the 454 and the wing over diesel especially as most diesel users don't even get 9 mpg on a good day. Oh and as for pulling power, I can climb like the best without problems.
Now if you want to run down the freeway at 75 your fuel range will drop drastically. One of the reasons the old 55 mph was incorporated was to save fuel, It worked then and it works now.
But overall if you reduce your speed you'll increase your range.

Also note the price difference between Gas and Diesel, and compare and price. Gas is on average 60 cents cheaper than Diesel, However I have seen Diesel as much as 92 cents a gallon more than Gas. Of which there is no justification, Diesel is cheaper to produce than Gas and the only reason it is costlier is profiteering.


signed the Double Nickel

Tow mileage is useless without weight and size of 5er!

I have a 1996 GMC K3500 SLE with a 7.4 (454) and a 4.10 rear end.
Prior to buying a 5th wheel, We spent hours researching for the best tow vehicle and best fuel economy available. As usual I was told Oh buy Diesel, It will give you the power for climbing. That is true but overall if you have a Diesel it costs you more in Fuel purchase and repairs. I have also read the Myth Busters report that Wings and other type of deflectors don't work.
We'll I beg to differ about Diesel is better and air deflectors don't work. I average 10.2 mpg using 87 octane gas and a Wing adjusted to push the air over the trailer. Prior to using the wing I averaged 8.5 mpg my average speed is 55. So I prefer the 454 and the wing over diesel especially as most diesel users don't even get 9 mpg on a good day. Oh and as for pulling power, I can climb like the best without problems.
Now if you want to run down the freeway at 75 your fuel range will drop drastically. One of the reasons the old 55 mph was incorporated was to save fuel, It worked then and it works now.
But overall if you reduce your speed you'll increase your range.

Also note the price difference between Gas and Diesel, and compare and price. Gas is on average 60 cents cheaper than Diesel, However I have seen Diesel as much as 92 cents a gallon more than Gas. Of which there is no justification, Diesel is cheaper to produce than Gas and the only reason it is costlier is profiteering.


signed the Double Nickel

The 6.4 is not noted for fuel efficiency. The 350 would have 3.73 diff and the 450 would be 4.30. I'm pulling 15,000 with TV in sig and would be happy if I averaged 9 mpg. I do feel there is a difference in fuel quality which also affects mpg besides the wind smoothness of the road and terrain.
There is also the problem with fuel availability as the 6.4 is only cleared for 5% bio and in some areas the fuel stations all have up to 20% bio stickers on their pumps.
I would love to trade my 09 6.4 for the newer 6.7 just to avoid problems with bio-fuel.
I have had 10 mpg on occasion flat ground good road and 55 mph, hasn't happened too often.

When towing a 5'vr it isn't so much about the weight as it is the height & frontal area.
Wind resistance plays more in MPG good and bad.

Somewhere between 5 and 15.

Allworth wrote:
Way too many other variables for any kind or realistic answers.

Yup, engine, fuel-type, height, etc, etc

Way too many other variables for any kind or realistic answers.