[Bandit12]

FWIW, I work in auto parts sales and I own a 28 Ram with the CTD so yes I use DEF. On our vacation trip last summer, I made sure the DEF tank was full before leaving home. We towed our 4000 lbs Jayco to Rapid City SD from NE Calif, a distance of roughly 1300 miles. We ran around for 9 days, putting a further roughly 600 miles on the truck without the trailer. My DEF gauge was reading 1/2 so I added another 2.5 gal jug before hooking up to head home. We towed the trailer back thru Wyoming to Hill AFB near Ogden UT, A distance of roughly 600 miles and used the same half tank of DEF. Filled up while in UT, traded the Jayco on on a Cougar the weighs about 2000 lbs MORE than the Jayco we had been in and towed the new trailer home, a distance of roughly 600 miles, using about 1/4 tank of DEF. Why the difference? Well, all the way across Wyoming, we were bucking about a 30 MPH headwind the entire trip. The harder the truck is working, the more DEF is used, just as more fuel is used. After talking with my regular wrench that I have service my truck, he explained to me that I need to treat DEF like milk. It will spoil. He advised that I wait until the DEF LOW light comes on, then refill the tank. According to my manual, the tank holds 5.5 gallons. When the light comes on, it will take 5 gallons, or 2 jugs.