Excessive DEF usage

gump1234 · June 20, 2022

I have a 2020 high country with the 3.0 duramax. It has ~35k miles. I like it and had no issues until a recent trip.

Last week I hauled my boat about 550 miles across Texas on the interstate. The boat is basically a bass boat and might weigh 5k. I drove about 80 the whole way on the interstate.

I filled the truck plum full of DEF right before I left. When I was about 5 miles from my destination the light popped on saying DEF extremely low and engine would derate soon. I never got any warnings prior to this like the ones that usually pop up and say 1000 miles left, 500 miles left, etc. I toggled through the dash display and the DEF gauge was completely empty. I saw an Oreillys and went and bought two 2.5 gallon jugs. It took one and a half jugs to fill it up. I used 3.75 gallons of DEF in 550 miles. What the heck?

I left the boat at the destination and drove home a couple days later on the same route and same speeds. When I got home the DEF gauge read nearly full. I dumped the other half of the jug in that was left and while it didn't start overflowing it reads completely full now.

Has anyone seen DEF consumption this high? I own three other vehicles that take DEF and I have never seen any of them use that much.

SVG · June 20, 2022

My normal tow with my boat (~5K) is usually no more than 40 miles each way. I've got a number of lakes very close to me.

So I never really notice any gross increase in DEF consumption in doing that.

The one time I noticed a massive increase in DEF consumption was when I was driving back to MT from Phoenix. I hit a massive snow storm in Wyoming with serious head winds. The truck was working harder than normal to maintain highway speeds due to this. The tuck never felt under powered though. About midnight, in a blizzard, I get a low DEF message. Wonderful. I was able to find a gas station in Crow Agency, MT. I can't remember exactly how much I put in but I was into the second jug for sure.

The consensus with these 3.0's is that they sip DEF during normal driving but chug it during towing.

TT331FB · June 21, 2022

I will use 5 gallons towing 7k# for 1000 miles.

gump1234 · June 21, 2022

I guess it isn’t out of line then but wow that is unusual compared to other diesels I have had. My Mack semi loaded to 80,000 lb consumes def at about the same rate. 4-6 gallons per 1,000 miles. My other diesel pickups use much much less even when towing.

I love my eco diesel but towing anything the eco goes out the window. Same exact trailer my 6.6 duramax or 6.7 power stroke get better mpg and use less def than the 3.0 does. Empty though the 3.0 blows them away.