Home Forums Hunting & Shooting Hunter's Campfire GMC 6.6 Duramax mileage?

For the guys that own them, what kind of mileage are you getting? Thanks!

My cousin has one. 3/4 ton 4x4. He gets 17-18 he said.

2024 3500 about 18’ish. As high as 21 but as low as 10/11 depending on the load. You could expect around 18 without a trailer.

I have heard pretty good on the newer ones...

I had a 2001 (?) with the LB7... it was a disaster.

FIL had a 06 model with 150k mi he said he just got it broke in and gettin 20mpg until some dumfuk took his front end off drivin wo headlights in at 5am🤦‍♂️

18 or so around town, and 24 on the highway. Helps if you don’t accelerate with a smoke cloud billowing out the pipes.

Mind is 2006, in town, short runs 11-14. Hwy unloaded 19 -- 21, depending on how fast it's going. Best mileage towing the boat to the coast and back, 17mpg. Boat and trailer are 3800 pounds. Mine is 100% stock, no mods..

20 on the interstate unloaded. 8-9 with 12-13k around home.

Average 11.8mpg in my 2019
3500 dually utility truck loaded with tools and tow a lot. Mix of interstate and local driving.
2019 mode
Pretty much same as my 6.0 gassers in same configuration. If it weren’t for towing equipment I’d go back to gas. Exhaust brake is worth the diesel alone.

Average 11.8mpg in my 2019
3500 dually utility truck loaded with tools and tow a lot. Mix of interstate and local driving.
2019 mode
Pretty much same as my 6.0 gassers in same configuration. If it weren’t for towing equipment I’d go back to gas. Exhaust brake is worth the diesel alone.

18/19 on my 2008 no load. 10/12 with trailer

Have 2 left ....not a lot of use anymore. 13-24 between town and high way.

But, But ......have had diesels since 1975. Will not own another.

They just do not pencil out.

I am on my second one. Current one is a 2013 denali. Gets 17.4 empty and 10.7 towing a 38 foot 5th wheel on flat ground.
Edit to add....towing without a head wind. We drove across indiana towing with a nasty head wind at 65 mph and got 7 mpg...lol

I have a 14. If I drive the speed limit it'll get high 19 ,low 20.
Most generally I'm over by at least 10 mph. So it's typically 18ish when not in town.
Pulling the fart box it gets 12-13.

Thanks guys!

Year?

The early 2007 might have been the best of the best. 20 MPG on semi-flat interstate. Maybe better now. But it sure went south for a decade.

Have a 2007 classic. 289,000 and is still my daily. 15-16 in town, 19-20 on highway.

The classics bring top$$

Last was a 2013 3500 dually. Got 14-16 running around. Right at 20 highway, about 10 pulling a 4 horse LQ trailer with 3 horses.

I just got rid of a 2006 LBZ; it had 160K on the odo. I was able to get 19-20 mpg on the interstate unloaded. Pulling a small trailer on the interstate, I'd get 14 mpg. Being a crew cab, the tank was smaller. I'd get about 375 miles on a tank of fuel made up of city/interstate driving.


Truck was all stock. Never been programmed and was running factory size tires.

I had a 2005 GMC 2500 LLY that I put a chip and upgraded exhaust, it got 23-25mpg on highway and 18 in town. I now drive a stock 2021 GMC 3500 and get 16 in town and 21 on highway. Highway is unloaded mileage.

15.2 on the gage .. that tells u all your ilde and run time... 19.8 if I run to Anchorage.. ..I run 85 miles a day 4 days a week...2004.5 Duramax twice a week 200 gallons of water....

I’ve got two, a 07 and a 06. Both get 18mpg hand calculated over the past 5 years. Fuel economy is better in the summer and worse in the winter, but that’s the average over a mix of hwy and city. They are great trucks.

Mine's a 2016 3500 and that's exactly where I'm at.

I had a 2011 stock that would get around 14.5 for mixed driving, maybe 17-18 on the highway, and 10-11 towing a 6k travel trailer.

I’m a Cummins guy, been driving current goat since 02. But wanted to say, this is the most completely honest sounding, totally believable mileage post I’ve ever read, hat off to y’all.
Usually when diesel mileage comes up there’s always “that guy” with unbelievable claims.

Hey Cisco, I am curious. What diesel pickup was out in 75? Ford started production in 84.
I currently have a 19 6.6 and if I behave myself and limit my trips to Montana I can stay right around 22 mpg. I just made a bonzi trip to Montana and back this last Saturday (785 miles) and I only got 20 mpg, but the roads were not good enough to let me travel my normal Montana speeds. When I do that my mileage drops to about 18 mpg. Now with the travel trailer on my milage drops to about 12 mpg.

You are right Blu Mtn, my first was an 85 Ford , not a75. However I have had about 8-9 Duramax Company trucks since then. My current '08 has had the emissions deleted and is chipped. THE ONlY ADVANTAGE TO DOING THAT , is the fact that I won't have to futz around with emissions setting plugged up.

We have gone to gas trucks , I don't drive he diesel too much any more, it is good truck , but diesels are too expensive to buy initially and maintain. When the advantage of diesel prices went away decades ago ....so did the advantage.

I liked diesels and have millions of miles in them , but no more.

Back when Ford introduced the diesel in 84 we were driving 81 one ton 4x4 Chevrolet's with the 454 in them. We were getting about 5 mpg. We bought the Fords and jumped to about 15 mpg and diesel was half the price of gas. It was a win-win for the farm. Through the years I have owned about 20 diesels of either Ford or Chevy and have driven about 10 one ton service trucks of all brands. But with the horsepower and fuel economy that the gas engine are getting now I don't know what my next pickup will be. I do guess I know what it won't be and that is a Dodge.

If the govt allowed a diesel to be a diesel, you guys would be getting much more power and much more mileage.

There's a fix for that in some places after warranty is gone.

Fixing a GM pickup is much more expensive than the same fix on a Ford. But still probably worth the price of admission.

I've got a '18 Denali. Getting 16-18 city and 22-24 hwy empty.

My late build 2006 LBZ would get 16-17 unloaded regularly with our bio-mass deezil fuel. I oddly picked up about 1 mpg after installing twin Kennedy centrifugal lift pumps, and was about to update the brainbox, when a guy made me an offer I couldn't turn down. If the truck would have had a 96" bed instead of 78", I likely would still be driving it.

Blu Mtn ,
I just remembered International was offering , a dealer option perhaps, a Cat diesel in their trucks. I looked at one at a dealer and did not care for the way it was installed. Don't remember the year.

One can buy an awful lot of gasoline ...for the costs one will have with a new diesel. We get awful good mileage with our new Fords.

I went with Ford , as GMC has had horrible QC issues. Ford may be no better. However , with 50K miles ...no problems.

I still have Chevy Suburbans and an old '52 P'up.

I had a Diesel Suburban that my wife drove the hell outta it.
Also, had a 1/2T Suburban with an Olds Converted diesel, GMC/s finest moment,

Could not keep tranny's in it . One well know trans outfit put several in under their warranty.

I probably have more small diesel truck experience than most.

I am pretty well versed in diesels, as I have a track loader, diesel tractors, ran a lot of diesel powered heavy 'chinery from 2 engine scrappers , D 8 dozers to finish compressors.

Some one mentioned "Fixing " the diesels after warranty is up for better mileage.

That is pure un- adulterated BS. I have been involved in some of these conversions and chips . More power no more mileage .
I don't get any better mileage with my Duramax. I do not keep my foot in it either.

What highway speeds? Are you using AT or highway tread type tires? I see folks saying they get over 20MPG w/3/4 and 1Tn diesels, but I've never seen it play out at the pump. In 350K Mi myself between 2 F250's, a 6.0L and 6.7L (w/3:31 gearing) I've never gotten either of them to make 20MPG+ over say a 200+ Mi all highway trip. That said, our interstate speed limit is 75 and I drive 79-80MPH with the cruise set, 75MPH on the non-interstate 4-lanes, and 70MPH on 2-lane highways. Maybe 60MPH and highway tread would get me to 20+? I'm not saying it can't be done, I'm just wondering how others make it happen?


Give or take, +1.5-2MPG on the highway eliminating DPF and EGR with tires and speeds remaining basically same/same.

I looked at that fuel usage screen after reading the post. It says 19.7 mpg. My last long trip, 1200 miles, it gave 24.5 mpg by actual computation. I bought this 2005 DuraMax Silverado last January. It’s a 2500 HD. Has that small back seat and the rear doors that open backwards. Fellow I got it from used it to pull a big camper. He put in some sort of chip. 136,000 miles when I got it, and it is like a new truck.

Don't know about the GM trucks, other than it cost twice as much to "fix" one of them, vs a Ford "fix".

Not sure about additional HP, but I went with a basic computer program that claims over 50hp.

I do know for a fact that my mileage immediately went from 13mpg to 17.5... I'll take that all day long.

My trailer pulling mpg went from about 11mpg to 14.5mpg.

I do not believe any of it !

More HP,.... mileage , perhaps a little better ....if not ripping around.

NO one, that is ,no one ,is gonna say not much diff after putting the money inna new chip and exhaust.

Dude, I don't know you, and you don't know me.

If you did, you'd know I don't BS and lie. There's just no reason to do so.

The numbers I stated are indeed truth as it stands before and after.

You can believe that or not. Frankly, I don't care which.

I used to have to start my Duramax ....with a pony motor.

Work for the epa? I have dyno sheets that the power side. When a diesel is tuned for efficiency you can’t help but increase mileage. No different than playing with timing on an old Chevy 350.

. I usually agree with much you have to say. But Duramax cost no more to fix than a Ford in the long run. Example 7.3 Ford and 6.6 Chevy. Glow plugs on the 7.3 and 6.6. Ford cost five times the dollars. I don't know about the 6.0 Ford or newer, because 6.0 was the last truck Ford will sell me! To each his own opinion!

I think we have the term "fix" mixed up.

To do the "fix" I refer to on my 2017 F350 6.7 diesel about a week ago, cost $1500.

My cousin who has a 3/4 ton Duramax told me to ask about getting his "fixed". My mechanic said he doesn't do GM "fixes" but had a friend who could, if the parts needed were to be had, but the cost of the GM "fix" would be closer to $3k.

My cousin took a hard pass at that price.

BTW, I was on my tractor today, and stopped by my pickup and started it up to see the avg. mpg as of today... I seems I recollected pretty close.

What speed and what tires? I’m not claiming at all that you don’t get what you say, just trying to figure out how to get there.

1.5-2MPG based on 215K Mi pre simplification and 20K post so far.

2014 2500 4X4 CC long bed, 14-18 empty, 10-13 pulling a trailer or 5th wheel. Just traded it on a 1500 with the Duramax. 28.5 MPG combined over 1K miles so far. Will see what it does with a small bumper pull.

Running no more than 75 on new Firestone 245/75R16 tires

Pretty much spot on with my 2011 as well. Towing my 11k lb boat I get 10-11 towing. 14k lb toy hauler drops to about 9.

2022 Chevrolet 2500 4x4
Have gotten 8 to 22 mpg. Towing 14K pounds to empty running @65mph with a strong tail wind.
Wind and idle time are a big factors also.

My hwy milage is running 70 mph. Running Michelin LTX tires inflated to 65/75 psi.
Two years ago we went to Yellowstone and the Tetons. Just followed speed limits, including SD and WY 80 mph with engine braking in the mtns.. Trip was 3400+ miles and mpg average was 20.7.
Florida trip included Smokey Mts.and Bourbon trail. Trip was 2576 miles and mpg average was 21.8.
I've been told that some Duramax gets better mileage than others.
Don't know if there is any truth to that.

I have a 09 Ford F350 CrewCab 4x4 about 100,000 KM i chipped it and increased my milage about 15 % or better , i do not use position 2 or 3 just keep it natural above 60 MPH fuel goes south. my normal truck weight is 9460 lbs or 4300KGs so i am always heavy. To increase my milage i went to 35 inch tires which increased my milage about 2.6%.
with the diesel and 35s there is no appreshial drop in torque or towing ability . Iam at 227,000 miles and still going strong.

Norm

Mine is an 01 Siverado duramax. 4x4 crew cab long bed dually and I keep a slide in in it full time. Average mpg runs 10 to 13 but when I watch my r foot Ive gotten up to 16.5. Around 170k on it.

2019, 2500 HD: 22-23, empty on open roads, 16-18 around home, in to town, 12-14 loaded pulling a horse trailer, all about18,00 pounds

How are you liking your new Nitto Exo's?

I get 15

I also have a tuner