Duramax 3.0L DEF usage

[Larisa Sult]

Has anyone been successful in finding an actual spec from GM in “normal” usage for DEF fluid?  I have a 2022 Chevy 1500 duramax 3.0L. It has 3300 miles on it and has used 11.5 gallons of DEF. Dealer says this is normal and also says GM does not have a spec. So how can we know what’s normal if there is no spec. The truck gets 32 mpg without the trailer and 16 with it. My DEF usage is 8% of fuel usage. Everything I find online says it should be about 2% of fuel usage. 

[newdude]

There isn't a spec.  Every owner will experience a different rate of DEF consumption based on how they use their truck.  

 

Emissions requirements changes since the mass introduction of DEF in diesels has now increased the amount of DEF used.  Towing (loading the engine) more is used during now.  

 

If the 2% rate you found was from the Cummins website, or was from another website, they likely refrenced that article.  ARTICLE - MB10033.pdf (cumminsfiltration.com)  

 

Note the date of emissions standards that was written was in regards to the 2010 emissions standards.  Lots has changed in 13 years.  

 

Here's the bulletin from GM.  Note they detail on the gauge and its possible inaccuracies due to the indicated level being a calculated level, and not a direct level like the fuel gauge.  

 

20-NA-082: Information on Excessive Diesel Exhaust Fluid (DEF) Usage

 

The current 2020 Silverado/Sierra is the first to have a DEF level gauge on the IP. This is the first time a customer can see a representation of how much DEF is in the tank up to the full capacity of the tank. This gauge does not operate like the float style gauge that you have in your fuel tank. Because of this, you may see some fluctuation in the gauge.  It may also take a few key cycles to register the correct amount in the tank after a fill event.  With the new segmented DEF level gauge, it is possible that after adding 5 gallons (18.9 L) of DEF that the gauge reads as a full tank after the fill event. However, if the actual level of DEF is just entering the last segment on the gauge, the gauge is likely to drop by one segment shortly after driving after the fill event. This could give an initial impression that the vehicle consumes a lot of DEF.   Every year that GM produces vehicles with diesel engines, the requirements to reduce Nitrogen Oxides (NOx) in the vehicle exhaust continue to get more aggressive. Because DEF is required to reduce the NOx in the exhaust, DEF consumption will increase as NOx reduction requirements increase.  When customers trade in an older model year diesel Silverado/Sierra for a newer model year, there will likely be an increase in DEF usage. DEF consumption increases as the newer vehicles meet the more stringent emission requirements for that model year. The amount of DEF usage is also a function of how hard the engine is working, or engine load. Because of this, it is more representative to compare DEF usage to the amount of fuel used, also a function of engine load, instead of miles traveled. In addition to engine load, other factors that affect the DEF usage rate are the humidity, temperature, and altitude where the vehicle is operating.    Under certain conditions, the ECM will increase or decrease the amount of DEF used based on learning or adaptive algorithms. In the event of a malfunction and SES light, the ECM may double or even eliminate the amount of DEF that is being used. This will continue until the vehicle is repaired and until the learned value in the ECM is reset. When towing a trailer or when the vehicle is heavily loaded, the vehicle will use more DEF per mile. While the DEF usage at any one moment is calculated instantaneously based on the amount of NOx the engine produces, the average DEF consumed takes much longer to adjust down after the heavy load is removed from the vehicle. When a customer sees a message stating ****** miles to empty, this is based roughly on the average amount of DEF used. If the vehicle is heavily loaded during that ****** miles, the range will be lower. Conversely if the vehicle is not heavily loaded, the range will be more than ******. For some customer usage scenarios, this can give the impression that the vehicle is using too much DEF when in actuality if you measure the amount of DEF consumed based on fuel consumption you will get a much more accurate measurement.

 

[redwngr]

They probably didn't fill it to the top at delivery. (common issue)

Does the 11.5 gallons include what is currently in the tank?

 

You are correct about DEF usage being in the range of 2% of fuel. 

 

Because of how the internals work, the def level indicator is not accurate enough to use for def usage calculation.

It should only considered as a rough indicator of def amount in the tank. 

(and an aftermarket device still gets it's level info from the same inaccurate level sensor)

 

GM did publish a bulletin in when def was introduced that indicated usage a little less than 2%.  

I wouldn't call it a spec, but more of a guide.

Since it is given as a % of fuel, that acknowledges that when working harder it will use more def

Permissible NOx levels are now lower. NOx managed by engine processes as well as exhaust treatment, but presumably the intended def consumption is a little higher than it was the 2011 LML. 

I'm not believing that the intended level has gone from 2% to 8%. 

Mine certainly doesn't use that much.

 

Are you using a metered bulk pump to fill def or are you using jugs?

 

Mine has over 30,000 miles. 

All def measured by a metered pump.

Last DEF fill was early December (up, it's gonna need some soon)

Without going out and checking my book, at last def fill it had lifetime usage rates of 26.5 mpg fuel and 1200 mpg def.

If my math is correct, that's about 2.2% 

 

The prior def using (LML and L5P) dmaxes I ran were a little under 2%.

 

 

 

Edited April 26, 2023 by redwngr

[Transient]

Your engine isn't broken in until 5,000 miles.  Let's wait a little bit before complaining. 

[Bubba10417]

My 21’ LM2 with 30,000 miles uses about 5 gallons every 6,000 miles or so. I rarely tow and mostly highway driving an hour at a time. 
I’ve owned it since 9,000 miles but have read the truck will regen a lot more I. The first 18,000 miles or so and thag could cause it. Hard to know what to believe without having someone knowledgeable that you can trust. But that is my experience 

[superdashdad]

I have 3500 miles on mine.  Put 1 2.5 gallon jug in it so far, probably ready for another one so I estimate I used about 5 gallons in 3500 miles or roughly 3.5% of fuel.  Mostly suburban / country / highway driving, no real city.

[Dpach]

It will drink DEF like a drunken sailor on leave when towing (programmed that way to meet California pollution regulations), so how many of those miles are towing?

[redwngr]

Still uses about 2% of fuel when towing.

 

''Range estimator' part of algorithm for def level display convince you otherwise. 

 

Big mistake on GM's part not to have it function like a fuel gauge.

[Cory Stewart]

I have a 2024 3500 dually I bought specifically for towing my 5th wheel, my 2020 gets about 12 mpg and a full tank of Def I can go well over 1000 miles with out worry towing the trailer, my new 2024 gets about 11 mpg empty and can go about 100 miles on a full Def tank while towing the trailer granted it gets about 5 mpg  with the trailer, It's been at the dealership since Tuesday and gm is saying there is nothing wrong.  Does anyone else this same experience with a 2024? I absolutely love my 2020 but this new truck is found lacking. 

[redwngr]

9 hours ago, Cory Stewart said:

I have a 2024 3500 dually I bought specifically for towing my 5th wheel, my 2020 gets about 12 mpg and a full tank of Def I can go well over 1000 miles with out worry towing the trailer, my new 2024 gets about 11 mpg empty and can go about 100 miles on a full Def tank while towing the trailer granted it gets about 5 mpg  with the trailer, It's been at the dealership since Tuesday and gm is saying there is nothing wrong.  Does anyone else this same experience with a 2024? I absolutely love my 2020 but this new truck is found lacking. 

Are you getting the 1000 miles to empty (and maybe also the 300 miles to empty) before adding DEF?

How many gallons are you adding to the DEF tank when 'refilling'. 

Are you using pump def so you know how much it takes to get completely full?

 

Trying to understand 'DEF miles per gallon'  --- rather than miles per tank.