I just completed a 3000 mile trip with my 2017 F250 and was getting a consistent 21mpg at 60 mph on the freeway, until passing through Billings MT when the mpg suddenly dropped almost in 1/2 to about 12. At first I thought I had encountered a strong headwind but when I pulled off I found that there was in fact a small tailwind. It really did feel like there was something dragging as I coasted down the off ramp. I looked the truck over and didn't see anything unusual so I continued on and was still getting 12mpg. After another mile or two I began to wonder if there was something going on with the 4wd as I had been switching between 4 and 2 due to icy on ramps so I pulled over again and switched to 4wd and then back to 2wd. After another couple of miles at 12mpg it suddenly jumped back up to 20mpg and has been OK since.

The only possibilities I have come up with for what caused this is either the 4wd was in some weird state or a brake was dragging. I talked to the service department at the local Ford dealer today and all they could say is that cold weather can cause a decrease in mileage, but that doesn't explain why it suddenly happened and then suddenly cleared.

Do you have any ideas of what might have been going on?

 

If it's a diesel, then it went through a regeneration cycle, it injects extra fuel during the cycle, and fuel economy drops off a cliff, then when it finishes the fuel economy returns.

 

Gee, that seems quite plausible to me. Wonder why the Service Manager didn't mention that.
My knowledge of engine technology is limited to being aware that the pistons go up and down, fuel is squirted in and away you go.

 

Welcome to the wonderful world of late model emission control diesel pickups!

 

Yes!! Regen,. I notice a drop in fuel mileage and can feel it in the acceleration/deceleration.

 

And somehow all this wasted diesel fuel is going to save the planet.

 

In a way.
The extra fuel burned helps maintain the part that keeps the soot particulates from being spewed out into the air.
So, not actually wasted fuel, and it doesn't do it that often or for that long.

 

Definitely you were going through a regen. It drops mpg to about 12 mpg on the highway then eventually it will jump back up when completed. Then you should be good for about another 500 miles before it does it again.

Ussualy another telltale sign that it’s going through a regen is you will get burning smell like brake pads are overheating or burnt coffee smell. That’s all normal.

 

Regen and mountains + winter fuel, is that what we're talking about here?

Bad mileage from the lie-o-meter?

As long as you're tank to tank cumulative miles are good, I wouldn't worry about it.

 

You'd have smelled it fairly quickly if a brake had been dragging.

 

Don't forget the plastic jug of DEF and the cardboard box it comes in. Super environmentally friendly

 

Generally, it's because: 1) They know less than their customers about vehicles, and 2) They don't care about you or your vehicle.

 

I was traveling one time in a remote area and thought I had plenty of fuel to make it to a certain town but my truck went into regen mode and I had to find a station much sooner.
I just went from Texas to California and my mileage always goes up when I get out of Texas. Even when driving in hilly Colorado I get better mileage than in Texas Is it the cetane in different places?

 

You're probably driving slower...

 

Yup, as I mentioned on another thread.....my 2015 would actually have a Notice pop up on the dash "Cleaning Exhaust Filter" but my 2022 doesn't do that. But when you're going down a long hill, in overdrive, and still indicating about 13 mpg, it's a sure tell sign you're in a regen.