My 550 DEF tank is not that big. I would have to check my Ford owners manual. You will get a warning on the dash display when it's getting low right before you loose engine power. What I do is carry a 1 gallon jug of DEF in that compartment as an emergency resource but when I travel 1500 to 2000 miles I always just add 2 gallons or so. There is no mpg it depends on how and where you drive.
__________________
|