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What is considered normal DEF usage for a 3.0L?

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I have taken my truck in twice to have it looked at for what I consider excessive DEF usage.  My truck is a 2021 Denali that was a dealer demo that I bought with 3200 miles on it.  The truck now has 11k miles on it and I have had to add 10gal of DEF.  I asked the service person what was considered "Normal" DEF usage.  The service rep stated that my usage was considered normal.  When I asked what was considered excessive, he stated that he didn't know.  


Little more background.  I have yet to tow anything with the truck.  Most of my driving is back and forth to work with one trip from Colorado to Alabama.  From what I have read on these forums, my usage would be considered normal if I was towing, which is understandable, but is this acceptable under normal conditions?


Thanks in advance for the help.

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I don't have much faith in the def level indicator.


Did you top it off to make sure it was full when you started measuring miles?  

Same as determining fuel consumption - must fill the tank, drive a bunch of miles, refill the tank -- then miles driven divided by refill amount.

Point is if it's wasn't full and 3200 --and/or not full at 11,000 we can't accurately calc mpg. 

If it was full at both, then it's (11000-3200) / 10 = 780 mpg 


What has the fuel economy been over the same period?



Mine was not full when delivered.

At 733 miles I went to a def pump location and topped it up. 


Since then it's been refilled twice - both times at a metered pump. 

Total miles 13,248  (since the top-up at 733)

Total def refills 42.7L (11.3 gal)  --- this ignores the first top-up at 700 miles 


def mpg 13248 / 11.3 = 1172 

First fill gave a little over 1400mpg, second was 900 something.

2nd fill had more towing, so more fuel  -- and more fuel burned requires more def.

Average fuel mpg (life of truck) is about 25.5 




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I just topped off DEF Friday. 45467 miles/28.68 gal DEF = 1585mi/gal. It used more DEF during the summer months as it got hotter. I haven't towed anything, just lots of highway miles.

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Definitely agree heat affects it more than fuel useage. Towing just creates more of both, but I use less towing at night in cooler temps than midsummer days.


For example, I used barely any def towing 5000 lbs with 1000lbs in bed for 800 miles to Florida in cool temps. 
Same trip in the heat unloaded used way more def.

Edited by Sqrls
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