High DEF consumption rate
Hi, new to this forum with a high DEF use rate question. My 2018 2500HD diesel is in the shop now to find cause for seemingly high DEF consumption when towing. High here means 5 gallons of DEF in 1400 miles. We were towing our 8800 lb Flagstaff travel trailer at 65 mph in cruise from the Gallup NM, up to the Grand Canyon, down to Phoenix, then across to El Paso and into Fredericksburg Tx. It is level travel, relatively, from Gallup to the Canyon, then down slope from the Canyon to Phoenix, then relatively level from there to Fredericksburg. Weather was mild, though Phoenix hit about 100 F for the one day we were there (unhooked city driving). Trip computer as well as odometer + fuel receipts show we averaged 11 mpg during the 1400 miles in question. So 5 gallons of DEF for about 130 gallons of diesel. I thought the expected rate was 1 gallon of DEF per 100 gallons of DEF.
I only have 8500 miles on the truck, post trip, so I have only added DEF once at about 5500 miles. Then I added 5 gallons in Gallup, and by Fredericksburg (1400 miles or so), I was getting the 'DEF low speed reduced soon' warning. Added 2 1/2 gallons more and booked the truck into the dealer when we got back. I did not get any early warnings coming into Fredericksburg, like the normal 1000 mile heads up message.
Has anyone else experienced this high DEF use under similar conditions? The dealer has confirmed no leaks, no error codes being thrown. They have called their GM tech support and been told "its possible under some conditions".
Appreciate your feedback as I get the truck back to day with a full DEF tank and some remaining concern.
2018 2500HD Z71 Diesel
Purchased: Sept 2018 new
Light local use
Tow 8800 lb travel trailer