I have owned a 2022 F250 with the 6.7-liter diesel engine for a year. It only had 4,700 miles on the odometer when I bought it. I know this sounds unbelievable but I’d get as high as 23 MPG on the highway when I first started driving the truck. For an unknown reason the truck’s MPG has now abruptly dropped to an average of 16 to 17 MPH. The truck is strong, runs smooth and no performance issues are noticeable. Your help/insights are appreciated.

 

My suggestion is to get OBD reader like "OBDLink MX+" so you can read live data and see the health of your truck so you can decide what to do on the next step, perhaps diesel fuel treatment might help.
Without the reader, if you can handle "upper" (at least) intake manifold removal, do it, just to check and see if your intake valves need walnut blasting. You can't use Berryman 2611 on a diesel engine, unfortunately.
Any car with direct injection engine (like yours) will need to walnut blast it every 50k or so. Just because you bought the truck with 4.7k miles doesn't mean it was a steal. 3+ years old vehicle with low mileage but zero maintenance is equivalent to a 2022 with 47k miles on it. Regardless of its mileage when you bought it you still have to top off all fluids, even if the previous owner had it in a garage and on a battery tender the whole time.
If it turns out to be carbon buildup at your intake valves, a permanent fix is to install aftermarket catch can yourself, and remove it temporary if you need to take your truck back to Ford for warranty or recalls.

Additionally keep an eye on the motor oil level, check and see if the level drops but no leaks anywhere.

 

Can we ask what kind of maintenance have you done/had done since the time you purchased it ?

 

When checking my fuel consumption this is how I proceed;
1. Park on a level fuel pad
2. Open the fuel cap
3. Fill the tank until I can see liquid fuel (not foam/bubbles etc) in the fuel filler neck.
4 Button it up and drive.
Note mileage and repeat. This will provide you with an accurate fuel consumption for that the fuel consumed.
Note that different fuel pumps provide various flow and pressures so the auto cut off will occur at different levels of fill in your tank.

I keep my tires well inflated too.

Regards,
Eric

 

Thanks for the advice.


 

Could you be comparing mileage in summer to mileage in winter ?

Winter warm ups can bring addl fuel consumption and possibly need for more regen cycles.

If these are not considerations because you might reside in a warm climate year round then it might not apply.