08 F350 dually horrible fuel mileage

Hillbilly Deluxe · Feb 1, 2015

Im not one to usually ask this type of question, but my truck has me stumped. I picked up an 08 F350 drw flatbed work truck the beginning of December, it was bone stock with 180k mi. The dpf/cat were stolen off of it while the dealer had it. So I straight piped it and got an sct x4 tuner and some gearhead tunes (street/hot street). Now I drove the truck about 400mi before I got the tuner/tunes. Even with the truck trying to regen it was getting about 14mpg. After the tunes (which are amazing btw) and me having fun I was getting 12mpg. I figured once I kept my foot out of it, the mileage would return. No luck. 12mpg and recently its getting worse. I checked the air filter and while it was a little dirty, it wasnt horrible. I reluctantly blew it out with some air and didnt really notice a difference but I'll be ordering a new Donaldson just to make sure, and changed the fuel filters as well, same results.

Friday I ran over to San Antonio from Houston. It was 600mi round trip for me. Empty on the way there running 70, 12mpg. On the way back towing an empty 24ft enclosed trailer I barely scratched 10mpg @ 65mph.

I understand this truck is heavy (9460 on scales) and it has 4.10s. Im running 285/70r17 bfg all terrains to help get the rpm down a bit. Im not asking for the world, but I feel like these #'s are really poor. Im doing everything I can to help mileage, not in the throttle hard, truck shifts around 1900-2100 rpm, which is a little high for me when Im empty, but its the trans tune file.

I dont feel like the truck is down on power at all. Infact it feels faster than my previous 08 Srw F350 which was over 1000lbs lighter and had an h&s tuner.

Maybe Im just crazy & expecting too much.

lincolnlocker · Feb 1, 2015

being a drw, i dont see it getting a lot better but id put a cai on it.. a tuned 6.4s need the air...

live life full throttle

Hillbilly Deluxe · Feb 1, 2015

Ive thought about that, but everything Ive read says the stock air intake/filter is sufficient for what I have. This truck isnt a hot rod, its a work truck. But at the same time, every little bit of fuel savings is $ in my pocket at the end of the day.

78f100 · Feb 1, 2015

Were you hand calculating or going off what the truck says? The lie o meter is usuall not correct when tuned from what I see. I doubt your gonna do much better than 12 on a 350 with 410s

tbsimmons · Feb 1, 2015

Slow down and it will come up some. RPM is a major factor in the 6.4 for mileage.

Hillbilly Deluxe · Feb 1, 2015

78f100 said:
Were you hand calculating or going off what the truck says? The lie o meter is usuall not correct when tuned from what I see. I doubt your gonna do much better than 12 on a 350 with 410s

I always hand calclulate, but the mileage calculator is always within a tenth of the hand calc.

As far as slowing down, I preach it all the time. But Im not not run 55mph out on the open freeway here in Tx when the speed limit is 75, because then Im just a traffic plug. I run hotshot, so I constantly have a 40ft gooseneck behind me. I can sit in the right lane at 65 and run with the flow of truck traffic.

It just sucks because at this mileage, I can run a class 8 truck and get the same fuel mileage. Something like a single axle volvo with a 12.7 Detroit/13spd will get an easy 9mpg hauling 20k lbs.

sootie · Feb 1, 2015

get a no limit air intake, i guarantee it will help some. but ya-rpms kill mileage on 6.4's, what you are getting is about right.

Powerstroke Man 6.4 · Feb 2, 2015

What your rpms at at 60?

I run around 1900 at 60 IIRC on my F-350 CCSB DRW with 4.30's with 19.5's and 31 inch tire.

I usually get 16-17 hand calculated empty.

13-14 with a trailer.

Spartan 310.

CAI and exhaust.

RedRice589 · Feb 11, 2015

Running H&S tunes but on a SRW with 4.10s towing a tandem axle 32' flatbed with 12k on it in panels through PA I only got 10. And I had 325/65/18s. Damn near a metric 35" so that's pretty normal. What psi is your boost gauge running. The 6.4s love to drink fuel

f350guy · Feb 11, 2015

Hillbilly Deluxe said:
Ive thought about that, but everything Ive read says the stock air intake/filter is sufficient for what I have. This truck isnt a hot rod, its a work truck. But at the same time, every little bit of fuel savings is $ in my pocket at the end of the day.

Not a chance the stock filter setup flows enough for the Hot Street from GH. I kept sucking the filter minder in on my AFE 54-11262 intake kit. Stock turbochargers. Basic air flow mods like high flow intake elbow, downpipe, etc.

Stuffed a 6.0 PSD filter (AFE 24-91036) on it from AFE's 54-11022 kit... no more filter minder movement. I had to remove the factory air scoop in the fender, not a big deal. This was less hassle for me is why I went this route over the No Limit.

As to the fuel economy? No idea. Maybe the winter blend we have currently? All three of my Diesel vehicles have less economy on the winter blend.

Hope it helps. Probably not.