Hello everyone,
I have a 2015 f250 fx4 with the 6.7 Diesel engine. It has about 14k miles on it. When I first drove it I was getting 14 in town and 17 highway going 75-80 going cross country. I had great mileage for the first couple weeks. Then I started to get 14 mpg driving highway going 65-70 and getting 12 in town. I have even deliberately tried to drive cautiously trying to get the best mpg I can and its just not happening. Everyone I talk to says they are getting around 15 in town and high teens to 20s highway. I took it to two different dealers and they say nothing is wrong and that everything is fine. Is anyone else having this problem or know what might be going on. Something has to be going wrong. Please help.
Thanks

 

The quality of the fuel and additives will have some effect. Are you relying on the truck to tell you the mileage or are you actually doing the math? Id suggest doing the math, if you're not just to see if its different.

 

Is your truck lifted? Do you have a tire/wheel package larger than stock?

 

What gears do you have? Did you put different tires on it?

 

Yeah it has a 4 inch lift with 33 inch tires so it's not that big of a lift and the tires aren't that much bigger to make the gas mileage that bad.

I calculated it one time by myself and used the mileage on a map and found out that I got 16 rather than 14 on the highway, but I feel that it still should be higher than that. It was a 10% difference because of the bigger tires.

 

It does seem low to me but I don't own a 6.7. I would hope it would do better. In my 08 F350 with a 2" lift and 35s I get 12-13 mpg highway. I got 13-14 with stock 33s. We have basically the same overall lift but I have bigger tires. I also have a 5.4 with 3.73 gears. That's why I say I hope it would be better. Everyone says diesels are a lot more efficient but based on these numbers it doesn't seem like there is that much difference. I'm sure while hauling or towing that's where the numbers will separate

 

not sure about the gearing, but my 2015 f250 6.7L, diesel, fx4 is pretty much stock. am 2nd owner. 36k miles, 1000 are mine. haven't towed or hauled anything of significance. i logged 17-18 mpg through town and 19-20mpg on the way home from dealer, as well as my 25-mile commute to work--both on the interstate. that was before the tonneau cover. after installing my tonneau cover, i'm at 18-19 in town, and logged 23 mpg going to work. i've noticed that i gain better mileage if i cruise-control at 68-69 mph. if i lock in at 70mph i drop back down to something like 18-20 mph. same kind of thing in town--there is something about trying to maintain a speed of around 45-50mph. i don't jump off the starting lines at traffic lights, i ease into the flow. i have punched it on the way to a fuel station every now and again, though. hahahaha.

 

I get 30 miles / 2 gallons if slight tail wind 😃

 

Check basics.. Air Filter, Fuel Filters, buying fuel at new location?

Your first mpg numbers (14-17) are about the same mpg as I get with a 6.7L.. I actually do a little better highway with 18-19 mpg.. City around 12-14
City MPG is so variable with traffic, lights, etc etc...

1-2 mpg can be easily affected both ways with environment, new gear added (Topper), Different driver, driving habits, tuning, filters, oil change (type synthetic or dino), temperature, humidity, load, faulty part(s) like the Mass Airflow Sensor, tire change, tire pressure, injector going bad, etc, etc, etc...

 

Larger tires, even a little, will make a measurable difference for sure. Increase in unsprung weight has drastic effects.

 

I had a oil change at the dealer and by mistake they put the blend in my truck. i always use synthetic oil and with the blend I lose about 5/10's per gallon over what I usually get. I don't have a lift nor 33's. Having bigger tires will make a big difference in MPG's. I also notice that newer tires get worse MPG's than older tires. It's because newer tires grip the road better than tires with 1,000 miles on them. I was told this buy a tire dealer. i found this to be true to some degree. Tires have lots to do with MPG's sometimes it has to do with tread patterns how wide they are or how much they weigh. Having a lift may have a effect on millage but I have no experience with them.

 

Going up one tire size may not due much, but going up to a monster tire will make an effect on a lot of things...
Steering, Suspension, Brakes, Tire Wear, MPG, your wallet, etc..