Poor fuel mileage on 2024 Duramax

[madweazl]

So I tried to drive conservatively and maintain 70mph on the highway (about 95% of this trips driving) and did pretty well. Wasn't able to hand calculate because of the trip duration but was pretty happy.  

 

Edited November 15, 2023 by madweazl
LOL; posted image of towing mileage by accident. Fixed

[BGooch]

On 11/15/2023 at 7:49 AM, madweazl said:

So I tried to drive conservatively and maintain 70mph on the highway (about 95% of this trips driving) and did pretty well. Wasn't able to hand calculate because of the trip duration but was pretty happy.  

 

 

[LowOnCash]

Hello All- 24' model showing 12-15 average 18.50 max so far but she's brand new. Nothing like the great mileage I got on my past Cummins, but I love the truck so much It would have to get under 10 for me to trade her.

 

Mike

Edited January 14, 2024 by LowOnCash

[ember1205]

21 hours ago, LowOnCash said:

Hello All- 24' model showing 12-15 average 18.50 max so far but she's brand new. Nothing like the great mileage I got on my past Cummins, but I love the truck so much It would have to get under 10 for me to trade her.

 

Mike

 

I bought my truck (gas) at the end of October. Here in New England, it's all winter blend fuel (gas and diesel) which results in lower MPG by itself - combine that with break-in period and the impact is more significant. My MPG is pretty poor right now but I'm not terribly worried about it as I absolutely expect it to come back up once we get back to summer blend fuels.

[David Sebolsky]

I have also noticed a large drop in fuel mileage. I traded in a 2022 3500 High Country for a 2024 3500 High Country. I am hopeful once the engine breaks in that the mileage will improve;  The 2022 did improve over time but it was not this drastic. 

 

2022 - Highway speeds on level ground with 60,000 > miles on the truck would average 28-30MPG

 

2024 - Highway speeds on level ground with 5,000 < miles on the truck now averaging 15-17MPG 

[LowOnCash]

43 minutes ago, David Sebolsky said:

I have also noticed a large drop in fuel mileage. I traded in a 2022 3500 High Country for a 2024 3500 High Country. I am hopeful once the engine breaks in that the mileage will improve;  The 2022 did improve over time but it was not this drastic. 

 

2022 - Highway speeds on level ground with 60,000 > miles on the truck would average 28-30MPG

 

2024 - Highway speeds on level ground with 5,000 < miles on the truck now averaging 15-17MPG 

 

David did you have the same 6.6 diesel in both trucks?  One thing is certain no one will ever see 28-30 mpg out our trucks. In fact 20-25 is even a stretch. It hurts when I consider my old 5.7 and 6.7 Cummins would obtain almost double of what I get with my 24' 2500.

 

Ride Safe - Mike

Edited January 18, 2024 by LowOnCash

[asilverblazer]

Curious if the more frequent regens are causing the lower AVERAGE mpgs.

 

I watch my 25 mile average mpgs go from 18-21 down to 10-12 from a regen. 

 

The average for a tank is usually 17-18.

[LowOnCash]

For sure, raw fuel dumped into the DPF for 10-20 minutes during regen. I'm not sure of the exact volume, would be interesting to know!

 

Mike

[Rick_]

My '25 3500HD is underwhelming for fuel mileage.  I got excited after GM replaced my ECM as it got 19mpg at 70mph with the winter front on.  The return trip was 15mpg for an average of 17mpg empty. 

I've watched the mpg go down by 5mpg during a regen but I don't go through DEF like the poster above.

Towing my 7000lb fiver shows 9.5mpg and my 5500lb boat is at 12.5mpg where my '22 baby duramax gets 14.5mpg towing the same boat.  Can't wait to put the boat behind the fiver and see how it works. 

[LowOnCash]

yeah it looks like big MPG is not going to happen with all these emissions choking the engine. Either way I'm liking my new Jimmy!

 

Ride Safe - Mike

 

 

 

Edited January 27, 2024 by LowOnCash

[Tom the carpenter]

Hi I have owned a 2007gm 2012ford 2015gmc a 2018gmc all diesels,they start out back then with only 330 hp and went up to 435.every one of these trucks averaged between 12.9 to 13.4 miles per gallon over the years of me owning the trucks .now I own the 2024 gmc with the new and improved engine with more horsepower an it averages 10.2 to 11.2 miles per gallon.love the hp hate the mileage 

[agent317]

What is everyone running for diesel fuel? I've been searching for #2 Diesel but most places are running B20 Bio Diesel now. 

[CamGTP]

Literally everything here in the midwest is Bio Diesel, I don't think you can buy it any other way other than offroad diesel.

 

It's 5-20% here in Minnesota and Diesel #1 or premium diesel usually is on the lower side but also will be better for the temps that see -20 degrees here.

[A Chap]

Just made a run from Palmer, AK to Fairbanks and back.  Shitty roads and used auto 4x4 majority of the trip, overall average was 19.2 mpg.  I'm ok with that. 

[PigRig]

Hey guys, I was hoping to revive this thread - I just picked up a 24 Duramax, and am getting 11-11.5mpg consistently.  Stop and go, highway, loaded or unloaded. 2,600 on the odometer so far.  

Reached out to Chevy in regards to the injector calibration and was told my VIN does not apply.  I've got a buddy with a 22 who is getting 17-24 mpg on the same setup, though he has a stealth module installed.  I really doubt the module would provide that kind of improvement.  

I'm open to any suggestions to get this pig chugging less fuel!