3.0 Duramax DEF consumption

topgear1224 · July 17, 2020

Having similar issues with very high DEF usage, Just bought the truck last month primarily to tow 25 ft travel trailer (4700 lbs dry, est 5700 lbs loaded). On our first trip with travel trailer from our home in The Villages to Pensacola, 400 miles. Not long after leaving the house got a message stating we had 2000 mile range on the DEF. Checked gauge and it showed 3/4 full. Just on the other side of Tallahassee, roughly 250 miles into the trip, message came on the we had 300 mile range, Gauge showed 1/4 full. 100 miles later, 50 miles from Pensacola, warning came on stating DEF tank was empty. Bought DEF once in Pensacola and filled it for trip back to The Villages. Same problem on the return trip, used up entire Def tank on 400 trip. Difference this time was when DEF ran dry max speed was immediately reduced to 65 mph. I estimate that I used about 8 gallons of DEF for the 4 day 1000 mile trip, 800 of that towing. DEF usage calculation was 1 gal of DEF for every 11 gal of Diesel. Significantly higher than what I was told DEF usage would be. During the entire trip the check engine did not come on. The check engine light finally came on the following day when not towing the trailer. Took vehicle to dealer and they have diagnose a faulty particulate sensor. Problem is the part is backordered with no estimated time of delivery. Have been told not to do anymore towing until part has arrived. Reading through other threads, it appears this engine might had not been tested fully under towing conditions. Emission systems appears to be overcompensating when fuel usage increases when towing, I have experience minimal DEF usage when driving truck not towing,

Yeah it's definitely a bad particulate sensor, problem basically is there are times when your engine will actually produce enough nox to require that massive of an injection, bit normally it's very short lived.

The only constant situation I could see doing that is if you were basically on the brink of overheating the engine. (Likely only would occur during a synthetic stress test. Ie 45 miles, full throttle, full load, 130°ambient, 15% grade at 55)

This engine was fully tested during Towing. GM just decided not to line the engine bay with a gold like material in order to increase the rating above 12k because they wanted to keep the price the same as the 6.2 upgrade. I've GCWR-ed this truck, there is plenty left on the table powertrain wise.

Here's where the problem lies, the engine is designed for efficiency unloaded.

once you begin towing with it your in-cylinder temperatures rise dramatically. With that increase in cylinder temperature there is an increase in nox production. The way they combat nox is with DEF.

issue with DEF injection is that it has to basically guess what's going to happen on the next cylinder cycle otherwise it accidentally releases a large amount of nox.

Because of the EPA crackdown, the OEM have to be overly agressive with injection. This is why we use so much DEF/gallon.

If you do a bunch of measured tests you'll actually find RPM has a huge impact on usage. If I keep shifts below 2.5k even with max boost and fuel my DEF usage isn't that bad per gallon of fuel (avg 14mpg like that though[emoji15]). Whereas if I use off road mode and pull some hills @55 even though my mpg goes up to the mid 20's my DEF useage sky rockets(3/4 tank over 1k miles) due to being always over 2,500 rpm. The truck is empty in both examples.

I'm actually surprised that they released the truck to you with there being an emissions issue. [emoji848][emoji848] I wonder if it's because now it's impossible for you to produce obnoxious nox since it's maxing out its injections.

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Moend · November 20, 2020

So this is my take on this, and it is based on your guys input - might be able to check if I have a DEF tank and able to look at:

1. There is no actual sensor that read a range of DEF level

2. DEF have tank have 2 sensor (Low, and Full)
3. The other ranges are calculated based on predetermined tables

4. Tables are dynamic and adjusted based on other factors (engine load, fuel consumption, attached trailers, etc)

To find out if this conclusion is accurate, when you get a low level add one gallon only. if the DEF gauge stays at low then the theory is correct.

I imagine it is something like gauges on the RV water tank (3~5) sensors "they are not sensors, just rods" and using the fluid to complete the circuit. it might be a very cost effective idea since an ultra sonic or resistive sensors might cost more than a small controller with few digital inputs on it, especially that DEF is not flammable. my 0.02 anyways.

Thank you!

Crazypontiac03 · November 21, 2020

On 7/12/2020 at 12:47 PM, Rubyralph said:

My dealership filled my DEF tank when I took delivery of my new 2020 Silverado 1500 3.0 Duramax, I now have ~1800 miles on the truck and the DEF gauge still reads full, when will I see a drop on the DEF gauge? Mostly highway miles not towing yet, average mileage 27.9 to 29.1.

Love the truck but I'm starting to wonder about my DEF usage???

I’m in the same boat after reading this entire thread I still don’t have a clue, but I also think it’s to early to tell for my situation I currently only have 1200 miles on the truck. According to the truck it hasn’t used any thus far.

Edited November 21, 2020 by Crazypontiac03

Grover67 · November 21, 2020

Did a trip this summer and maybe used between a quart and 1/2gal in 1700 non towing miles. Did the update after I got back and haven't seen much of a difference

-Grover67

BurnsMax · November 22, 2020

The gauge is in inaccurate, mine has been all over the place. It was half full and there was a pop up message stating I only had 625 miles left until reduced speed. I have also had it go from full to half and then a day later 3/4 full. I have almost 8k miles and have added 5 gallons. When it had the pop up message I aded 2.5 gallons and it stayed at half full

chris84 · November 26, 2020

On 11/20/2020 at 9:53 AM, Moend said:

So this is my take on this, and it is based on your guys input - might be able to check if I have a DEF tank and able to look at:

1. There is no actual sensor that read a range of DEF level

2. DEF have tank have 2 sensor (Low, and Full)
3. The other ranges are calculated based on predetermined tables

4. Tables are dynamic and adjusted based on other factors (engine load, fuel consumption, attached trailers, etc)

To find out if this conclusion is accurate, when you get a low level add one gallon only. if the DEF gauge stays at low then the theory is correct.

I imagine it is something like gauges on the RV water tank (3~5) sensors "they are not sensors, just rods" and using the fluid to complete the circuit. it might be a very cost effective idea since an ultra sonic or resistive sensors might cost more than a small controller with few digital inputs on it, especially that DEF is not flammable. my 0.02 anyways.

Thank you!

I believe there is a sensor, but there is a programming issue between it & the "gauge" display.

I can watch the DEF level drop on my I-Dash as you would expect when putting on miles. The gauge on the truck display had been going down & then went back up to 1/2 while my I-Dash read 0.

redwngr · November 27, 2020

On 11/21/2020 at 8:12 PM, BurnsMax said:

The gauge is in inaccurate, mine has been all over the place. It was half full and there was a pop up message stating I only had 625 miles left until reduced speed. I have also had it go from full to half and then a day later 3/4 full. I have almost 8k miles and have added 5 gallons. When it had the pop up message I aded 2.5 gallons and it stayed at half full

For sure the LML had multiple sensors.

With the Gm Tech2 there is a screen that would show which them as either 0/1, ( or on/off...).

Pics of the screen were posted on several of the dmax and diesel forums a few years ago.

I haven't heard if the L5P and the LM2 use the same system, but I suspect they do.

My dealer didn't fill this LM2 at delivery. Said they only add a jug or whatever...(that dealer doesn't have bulk)

I'm still under 1000 miles, but decided I'd go to a bulk location and fill it so I can get a more accurate estimate of how much it uses.

Driving duties are similar, and mpg appears that it will be 20 - 25% better than the LML and L5P that I ran.

I'm expecting def consumption to be an improvement on the 1100 -1200 mpg that I got running them.

BJ Niceguy · December 9, 2020

OK, the gauge is crap. I have 2020 3.0 & have 21K on it (about 1/2 towing). Mine takes forever to work down to 1/2 full on the bars, then almost instantly drops to one bar & throws low alarm. I bought a OBI plug in thing and it reads the def remaining. On mine, when the def tank drops 1st bar, it is really at about 80% remaining, then drops about 10% for each bar till about 1/2 on gauge. On mine when gauge reads 1/2 I am between 45% & 52% (the lower the tank gets, the more the OBI bounces around, assume sloshing in tank). Anyway, when mine hits 42% to 45% it drops to 1 bar & throws low alarm. I can usually BARELY get a 2.5 gallon jug in it & other times if filling at truck stop might get 3 gallons in. I have been in situations where I could not just stop & add, so ran past the 1 low bar & towing it dropped to empty & kinda locks up teh lower part of gauge and starts count down to speed reduction. I have never added more than 3.8 gallons.

On Def usage. Mine does not use much when not towing. When towing, how hard I am driving makes huge difference on consumption (as it does with mileage). If towing 5K enclosed trailer at 60 on 2 lane road, the def usage is probably 1/2 of what it is running 75+ on freeway (big difference in mileage too). I have had a 2013 with 6.2, 2016 with 5.3 & now the 2020 with 3.0. For me the 3.0 is hands down the better towing truck.

My biggest bitches with truck are the Def gauge & having to push the stop button every time start truck so it does not shut off at lights when not towing

SRNicholson · March 4, 2021

I had an interesting drive towing a trailer yesterday for the first time. I put a full jug of DEF in the tank 2 days ago and it read 3/4 full. After 450 km of driving my dash suddenly displayed the message below. I left it on the screen until the end of the trip and the remaining km went down very rapidly. I drove another 75 km and the remaining count went down 325 km.

I was confused as to why this popped up at all, and then surprised as to the rate at which it went down. End of the trip the DEF level only went down to 1/2 showing on the level.

Best thing I did find was that the truck towed a 4500 lb trailer magnificently. 1500rpm most of the time and 2100rpm on hills. Shifts were still smooth as ever even going uphill. Fuel consumption was 16L/100 km (15 mpg) which is far better than I ever saw with my 5.3L 2012 when towing.

Any idea why the message popped up at a random time like that? I'm guessing the computer determined that the DEF usage rate was excessive and it displayed this as a warning.

redwngr · March 4, 2021

1 hour ago, SRNicholson said:

I had an interesting drive towing a trailer yesterday for the first time. I put a full jug of DEF in the tank 2 days ago and it read 3/4 full. After 450 km of driving my dash suddenly displayed the message below. I left it on the screen until the end of the trip and the remaining km went down very rapidly. I drove another 75 km and the remaining count went down 325 km.

I was confused as to why this popped up at all, and then surprised as to the rate at which it went down. End of the trip the DEF level only went down to 1/2 showing on the level.

Best thing I did find was that the truck towed a 4500 lb trailer magnificently. 1500rpm most of the time and 2100rpm on hills. Shifts were still smooth as ever even going uphill. Fuel consumption was 16L/100 km (15 mpg) which is far better than I ever saw with my 5.3L 2012 when towing.

Any idea why the message popped up at a random time like that? I'm guessing the computer determined that the DEF usage rate was excessive and it displayed this as a warning.

Temps below about -11C when this was going on?

SRNicholson · March 4, 2021

8 hours ago, redwngr said:

Temps below about -11C when this was going on?

Forgot to include that info - about +5C at the time.

Luke L · June 16, 2021

I have 3900 miles on my 3 liter Duramax and have towed roughly 800 miles with it. 700 miles with a 5500lb trailer load and 100 pulling a fishing boat. I have used 7.5 gallons of DEF so far. I was going to take it into the dealer and complain about the DEF usage, after talking to the dealership owner who returned my call I decided to cancel the service appointment and run the truck for another 5-10,000 miles and monitor the DEF usage. I was told that higher DEF usage is normal while towing and breaking in the motor. Initially I was figuring 5 gallons per/oil change, which is what I was told to expect when I bought it but that apparently is with no towing. Price per mile is more than I was expecting but it does pull great and I made 11 to 12 mpg pulling a 5500lb trailer at 70-80mph. I will wait to see how the def usage is after the truck has 10,000 miles on it and go from there. I average 16-21 mpg in town all depending on how I drive it. And have gotten 23 on the highway at 70mph.

Edited June 16, 2021 by Luke L
spelling

Dersch · December 9, 2021

I have 12k miles on mine. I have added 10 gallons total to mine maybe 12.5 can't remember.. i do 90% highway.

1500 miles ago i filled it up pretty much full and its saying i only have 150 miles left... this seems like way too much??

I filled it up day one full that lasted me close to 5k-6k moles. Ever since then i feel every 2000-2500 miles it needs filled up.

Im about to fill up the tank full at 12k miles and will monitor how many miles it lasts.

tomthetrex · December 10, 2021

I have noticed that I get significantly more use of the DEF if I use the AC Delco version I buy from the dealership as opposed to the stuff you get at the store. I am unsure why.

redwngr · December 10, 2021

On 12/8/2021 at 8:42 PM, Dersch said:

I have 12k miles on mine. I have added 10 gallons total to mine maybe 12.5 can't remember.. i do 90% highway.

1500 miles ago i filled it up pretty much full and its saying i only have 150 miles left... this seems like way too much??

I filled it up day one full that lasted me close to 5k-6k moles. Ever since then i feel every 2000-2500 miles it needs filled up.

Im about to fill up the tank full at 12k miles and will monitor how many miles it lasts.

I'm a little over 16,000 miles.

Having read complaints about the segmented level / range indicator and knowing that my dealer did not completely fill the tank, I topped it up at about 700 miles.

Since then 2 refills for a total of 11.27 gallons, covering 13,248 miles.

DEF mileage is 1175 mpg

Currently, life of truck fuel mileage for currently is 25.6.

DEF usage is a little over 2% of fuel.

On one of the fills, I ran it til it thought it was empty and gave the 'miles til speed limit' warning.

The 3.0L holds 5.3 gal. (L5P 6.6 holds 7.0)

For the 3.0, the segments on the 'full end of the level/range indicator are about 0.5 gal each.

At the lower end the last 2 full size segments are about 1 gal -- so 1/2 full occurs sometime when there are 2 segments light and before there is only one segment lit.

DEF consumption is related to fuel consumption (since more fuel burned means more NOx to be treated).

If fuel mileage doesn't change much the consumption shouldn't either.

The 'range' part of what it displays assumes that future mileage will reflect recent past mileage -- so if it's been towing, it's gonna figure the def range is lower.

IMO, the only good way to determine DEF mileage is the fill-drive-refill-calculate method.

This gauge just gives a rough idea about what it might hold.