2018 F250 Def tank size doesn't seem to match

[wermlr75]

I recently purchased a 2018 F250 Powerstroke. According to the manual listing, my DEF tank has a capacity of 7.4 gallons. Yet when my gauge says I'm half full and I add a jug (2.5 gallons), it now reads full. Is there some sort of hidden reserve or did they change tank sizes mid-year or what?

[Semperfi24]

We had a similar experience when we had a 2019 F250 diesel. When my gauge was half a tank, 2.5 gallons would then read full. I think it is simply a design to save the user from themselves. That way if you push the limit (to empty), you still have 2 gallons left. Thats just me taking a guess and making assumptions. As in the tank will read E for the first 2-2.5 gallons of def. Adding 2.5 gets you to "half" (but you actually have 5 gallons). Another 2.5 gets you to full (but you actually have 7.5 gallons). Just my personal practice, is to put 2.5 gallons in when I get to half a tank.

[wermlr75]

Thanks. Between that and how long it takes the gauge to register that I've added something (about 25 minutes), I wasn't sure how much to trust the gauge.