Join Date: Apr 2018
Location: St. Paul, Minnesota
Early on in my mileage I had some weird fluctuations like that with DEF DTE (no longer have that happening anymore, and it didn't happen for very long), but did not experience the fill level amount in the display changing like you describe as far as I can recall.
I would not be too concerned over it. Just keep an eye on it. I personally add a 2.5 gallon OEM Motorcraft jug every time my DEF gauge is ~50% full. The DEF tank is 5.5 gallons capacity.
I wouldn't want to run the truck below 1/4 tank full on DEF for fear of ending up in limp mode if the truck decided not enough DEF (thus my practice of refilling to full when it reaches 1/2 full).
2018 Ford F-150 King Ranch FX4 3.0L Power Stroke 4x4, Long Bed & Trailer Tow Mirrors | Spray-in & Wheel Well Liners & BAKFlip CS/F1 & BAKFlip BakBox 2
ForScan Mods: DPF Full %, Bambi Mode, Show Temps Above Gauges, Operator Commanded Regen (OCR), more to do...
Traded In* ---> 2010 Ford F-150 King Ranch 5.4L Triton, LINE-X & BAKFlip CS/F1