Excessive DEF consumption, 2019 Denali Duramax - Page 2 - Chevy and GMC Duramax Diesel Forum
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post #11 of 18 (permalink) Old 09-30-2019, 06:49 AM
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GM has issues with the DEF gauge readout. I know mine is a 2020 BUT it happens on the earlier 18 and 19's as well. Mine jumps around even when it is almost full shows half or on a recent trip gave me the warning of xxxxx miles until empty. It took 1.4 gallons to fill it to the top when showing almost empty. After filling went to half then 2 days later went to full.

Point is it is not accurate and I carry DEF all of the time. Gave GM the notification letter (Dealer got a copy as well) per the instructions, call to them verified and have a case number now. Pursuing this Dealer under the Vernon Articles (Texas LL). The software was flashed on the 1st attempt did nothing and waiting for the strike to be over and the repair backlog at my dealer which is one of the biggest ones GM has because of parts non availability. This will be the 2nd attempt out of 3 and the Dealer is working with GM to determine what the next repair attempt will entail.

Do not want to be in the middle of nowhere and the truck decide it is out of DEF and goes into limp mode. Will just let them replace it if they cannot fix it.

2020 GMC Denali 2500
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post #12 of 18 (permalink) Old 09-30-2019, 07:29 PM
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I too maintain a spreadsheet. On my '19 with 7,800 miles I'm getting 770 miles/gallon. About 70% of miles in town, 30% hiway and towing

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post #13 of 18 (permalink) Old 10-01-2019, 09:36 AM
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Quote:
Originally Posted by mhs4771 View Post
OK, here's my calculations: '18 High Country Dually, 98% of mileage of just over 15K pulling heavy approx 19.5K pounds.

I wait until I get the 30% DEF warning and at that point I can dump in 5 Gal of DEF. Just did the cal and I'm burning

a Gallon of DEF every 471 miles, that's a lot more than my '11 LML did pulling the same weight.


That would probably be about right. How many gallons of diesel did you burn over the same time. Def usage is usually 1-2 % of diesel usage.

One guy on another forum said the def could be diluted to about 66% of normal def and it would still work fine. That would be 2 gallons of def and a gallon of distilled water. But I wouldnít do this in a real cold climate.
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post #14 of 18 (permalink) Old 10-01-2019, 09:51 AM
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Originally Posted by MIkey52 View Post
One guy on another forum said the def could be diluted to about 66% of normal def and it would still work fine.
I always find these posts somewhat humorous as with no data and just some "person" on the internet says ok do "this" some people actually do it. When something goes wrong and for whatever reason they (GM warranty issue only) check the DEF fluid just like they do the fuel and it is not to specification -- you are out of luck.

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post #15 of 18 (permalink) Old Yesterday, 08:13 AM
 
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Based on 20k miles of driving with all fillups (Diesel and DEF) recorded, both towing and non-towing, my 2018 L5P burns DEF at approximately a 2.2% rate. At that rate, I burn about a Gallon of DEF for every 45 gallons of fuel.
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post #16 of 18 (permalink) Old Yesterday, 01:14 PM
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Quote:
Originally Posted by monkeyman View Post
The full DEF tank is supposed to last 5000 miles!, I get at least 3000
Depends on how hard it is working.

If truck fuel use goes up, so will def use.

2018 GMC 2500 L5P CCSB 4x4 Denali - Mineral Metallic; previous '11 LML, '10 LMM and 04.5 LLY
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post #17 of 18 (permalink) Old Yesterday, 01:27 PM
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Quote:
Originally Posted by MIkey52 View Post
One guy on another forum said the def could be diluted to about 66% of normal def and it would still work fine. That would be 2 gallons of def and a gallon of distilled water. But I wouldnít do this in a real cold climate.
Quote:
Originally Posted by Busa Dave View Post
I always find these posts somewhat humorous as with no data and just some "person" on the internet says ok do "this" some people actually do it. When something goes wrong and for whatever reason they (GM warranty issue only) check the DEF fluid just like they do the fuel and it is not to specification -- you are out of luck.
Saw that post too.

The part I found amusing/curious it that DEF is already 'diluted'....(2/3 is water, 1/3 is liquid urea).



FWIW, one of the reasons for the existing ratio is because that ratio freezes a low temp (about 12*F) and at the ratio used it will not 'salt out' during the freeze thaw cycle.

https://www.cumminsfiltration.com/si...es/MB10033.pdf

2018 GMC 2500 L5P CCSB 4x4 Denali - Mineral Metallic; previous '11 LML, '10 LMM and 04.5 LLY
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post #18 of 18 (permalink) Old Yesterday, 03:57 PM
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I haven't calculated how much Fuel I've used but I've had my 2019 since August 6, 2019 I just rolled over 4900 miles and I've put 4 x 2.5 (10 gallons) of DEF in it so far. They swore it was full when I left the lot but based on some of your comments it probably wasn't. Of that 4900 miles I did 1300 miles pulling my 38' 10K lb travel trailer and got a whopping 7 miles per gallon doing it. I hear wait for the break in but I traded my 2018 w/48K miles on it for this 2019 (long story) and it never got better than 7-8mpg pulling. Anyway, I know this is about DEF but seems based on some of your calculations for 10 gallons of DEF I should have gone 7000 miles. I'd say I'm using a lot. I used a ton on that 1300 mile trip as I had to stop about 800 miles in and add 5 gallons. Thank God I found a 24 hour Wal-Mart in the middle of no where cause I was stupid and started the trip without a spare bottle. It went from you have 999 miles to go to you are about to have problems in about 30 miles. It seems to be using quite a bit. I'll be keeping an eye on this and this post to see what you guys come up with.
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