[Mark IV]

The urea (DEF, Diesel Exhaust Fluid) is no big thing. You use 2-3 PERCENT DEF to fuel so for every 100 gallons of fuel, you use 2-3 gallons of DEF. DEF is NON specific, all is the same so buy it where you want. Ford is providing DEF no cost during warranty.

Tuning the engines for DEF allows much of the emissions cleanup to be "downstream" of the engine thus allowing increased power, better economy and a MUCH wider powerband and "sweet spot".

I talk to guys with class 8 tractors on DEF that have seen 10% increases in fuel economy and believe me a trucker will KILL for 10 percent!