High DEF consumption rate - Chevy and GMC Duramax Diesel Forum
2017-19 GM T-K2 Platform Performance Parts Discussion Discussion of Performance Parts For the '17 and up L5P Duramax Trucks No Advertising

LinkBack Thread Tools Display Modes
post #1 of 3 (permalink) Old 05-08-2019, 08:17 AM Thread Starter
Join Date: May 2019
Posts: 3
High DEF consumption rate

Hi, new to this forum with a high DEF use rate question. My 2018 2500HD diesel is in the shop now to find cause for seemingly high DEF consumption when towing. High here means 5 gallons of DEF in 1400 miles. We were towing our 8800 lb Flagstaff travel trailer at 65 mph in cruise from the Gallup NM, up to the Grand Canyon, down to Phoenix, then across to El Paso and into Fredericksburg Tx. It is level travel, relatively, from Gallup to the Canyon, then down slope from the Canyon to Phoenix, then relatively level from there to Fredericksburg. Weather was mild, though Phoenix hit about 100 F for the one day we were there (unhooked city driving). Trip computer as well as odometer + fuel receipts show we averaged 11 mpg during the 1400 miles in question. So 5 gallons of DEF for about 130 gallons of diesel. I thought the expected rate was 1 gallon of DEF per 100 gallons of DEF.

I only have 8500 miles on the truck, post trip, so I have only added DEF once at about 5500 miles. Then I added 5 gallons in Gallup, and by Fredericksburg (1400 miles or so), I was getting the 'DEF low speed reduced soon' warning. Added 2 1/2 gallons more and booked the truck into the dealer when we got back. I did not get any early warnings coming into Fredericksburg, like the normal 1000 mile heads up message.

Has anyone else experienced this high DEF use under similar conditions? The dealer has confirmed no leaks, no error codes being thrown. They have called their GM tech support and been told "its possible under some conditions".

Appreciate your feedback as I get the truck back to day with a full DEF tank and some remaining concern.


2018 2500HD Z71 Diesel
Purchased: Sept 2018 new
Light local use
Tow 8800 lb travel trailer
Diesel18 is offline  
Sponsored Links
post #2 of 3 (permalink) Old 05-10-2019, 06:21 PM
Join Date: Mar 2018
Posts: 6
I don't know the exact ratio of DEF/fuel but it they should pretty much track. I usually see around 800 mpg on the DEF when driving unladen, but that drops to about 400 mpg when towing heavy.

I used 4.5 gallons of DEF towing 12k enclosed trailer the length of the AlCan Hwy (1800 miles)

I would say what you are seeing is slightly elevated usage due to the (comparatively) low miles. Mine got a bit better around 10k
dilpickle13 is offline  
post #3 of 3 (permalink) Old 05-11-2019, 07:39 AM
Junior Member
drzoo2's Avatar
Join Date: Jun 2010
Posts: 32
Thread on this issue from a month or so ago...


Sent from my HTC U11 using Tapatalk

Stock '17 L5P Chevy, Midnight Edition
drzoo2 is offline  
Sponsored Links

Quick Reply

Register Now

In order to be able to post messages on the Chevy and GMC Duramax Diesel Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:


Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode

Similar Threads
Thread Thread Starter Forum Replies Last Post
Excessive DEF consumption? Siorus 11-16 LML Duramax Powertrain 42 06-25-2017 07:26 PM
DEF consumption varies greatly elkhornsun 11-16 LML Duramax Powertrain 20 11-11-2012 10:30 AM
No Codes, High Smoke, High return rate Fenny76 04.5-05 LLY Duramax Powertrain 4 06-11-2012 05:08 AM
DEF consumption rates. Tail_gunner 11-16 LML Duramax Powertrain 42 05-31-2012 08:59 PM
Does anybody know the fuel consumption rate at Idle? coreyperez 07.5-10 LMM Duramax Powertrain 6 10-19-2009 09:58 AM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

For the best viewing experience please update your browser to Google Chrome