Running out of diesel exhaust fluid is about as dumb as running out of diesel fuel. Engine manufacturers set DEF burn rates at about 2 to 5 percent of fuel burned. (For every 100 gallons of diesel a machine consumes, it will burn 2 to 5 gallons of DEF.) So multiply the fuel consumption of a machine over a period of time by 0.03 to 0.05 to estimate how many gallons of DEF to have on hand. Dealers can give you some preliminary DEF burn rates, and you can do your own tests on a new machine. Just don’t run out.
More Machine Operation tips from “How to Do Everything Better”