five Report post Posted May 22, 2016 Does anybody have any idea how much DEF these diesels use as related to fuel burn? I spent 15 minutes on the phone with Detroit Diesel...he had no idea. On the internet, I found that the big tractors (18 wheelers) have a dose rate of about 2%. They use 2% DEF, as an example, 3 gallons of DEF for each 150 gallons of fuel. My DD 13 is 12.8L so I assume it would use about the same amount of DEF as the Cummins ISM/ISX. Thanks. Share this post Link to post Share on other sites
dickandlois Report post Posted May 22, 2016 59 minutes ago, FIVE said: Does anybody have any idea how much DEF these diesels use as related to fuel burn? I spent 15 minutes on the phone with Detroit Diesel...he had no idea. On the internet, I found that the big tractors (18 wheelers) have a dose rate of about 2%. They use 2% DEF, as an example, 3 gallons of DEF for each 150 gallons of fuel. My DD 13 is 12.8L so I assume it would use about the same amount of DEF as the Cummins ISM/ISX. Thanks. Five. The use rate will be close. Sure it will very slightly because the fuel burn can very depending on load and MPG numbers. That leaves some variables as all the gearing ratios very over chassis. So each owner will need to monitor us rate and get an average of usage. Also the DEF tank size can very. Rich. Share this post Link to post Share on other sites
kingfr Report post Posted May 22, 2016 My coach, with a Cummins ISL 450 uses about a gallon of DEF every 310 miles. I have averaged 7.1 MPG since new on this coach. This usage does include generator fuel usage, so the actual miles per gallon of DEF is probably a little higher. Share this post Link to post Share on other sites