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Determine Your DEF Consumption

Determine Your DEF Consumption

If you know your vehicle's average fuel consumption, you can easily calculate the amount of DEF that will be used.

DEF consumption is directly related to fuel consumption. Manufacturers suggest a rate of around 2% to 3%, which roughly equals out to about 2 or 3 gallons for every 100 gallons of fuel used. The expert opinion is that performance comes down to factors such as road, route, and service. 

Calculating DEF consumption allows you to maintain high fuel efficiency. It is important not to allow the a vehicle DEF tank to become completely empty. It should be refilled when 2-3 inches of DEF remains inside. It’s recommended that drivers refill DEF at least once in every third time they refill their tanks.

Diesel Exhaust Fluid Refill

Is the DEF usage rate the same for all engine manufacturers?

The DEF usage rate does rage slightly amongst engine manufacturers. While most engines will have an average dose rate of 2% of diesel fuel consumed, the dose rate may vary from 1% to 3%.

So how many miles can a truck expect to travel on one gallon of DEF?

Most vehicle's tanks require one gallon of DEF for every 50 gallons of diesel fuel, and one gallon is expected to last between 300 to 500 miles.

Medium Duty Truck Consumption Example

  • Annual miles for average truck = 50,000 miles
  • MPG for average truck = 8 mpg
  • 50,000 miles / 8 mpg = 6,250 gallons diesel fuel per year
  • DEF usage at 2% of fuel consumption = 125 gallons of DEF per year
  • 125 gallons / 10 gallon DEF tank (average size) = 13 DEF fill-ups per year

Heavy Duty Truck Consumption Example

  • Annual miles for average truck = 120,000 miles
  • MPG for average truck = 6 mpg
  • 120,000 miles / 6 mpg = 20,000 gallons diesel fuel per year
  • DEF usage at 2% of fuel consumption = 400 gallons of DEF per year
  • 400 gallons / 20 gallon DEF tank (average size) = 20 DEF fill-ups per year

Overall, DEF consumption is expected to be approximately 2% of fuel consumption, otherwise thought of as a 50 to 1 ratio, but overall it is depending on vehicle operation, duty cycle, geography, load ratings, etc. For every 50 gallons of diesel fuel burned, you will use 1 gallon of diesel exhaust fluid.

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