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Old 08-25-2019, 07:35 PM   #1
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2019 Duramax fuel economy

I thought I'd post some fuel economy numbers for my 2019 Chevrolet High Country crew cab 4x4 dually with the Duramax diesel and Allison transmission. I'm just doing this so that anyone considering the new diesel (L5P since 2017, and continuing with only cooling system changes primarily into 2020) will have a basis for reference if they are interested.

The dash on the Chevy shows a 50 mile avg fuel economy number. That's been at 22.7 for a long time. On a trip yesterday from The Dalles, OR to Seattle, WA I managed to push that number up to 24.5 after coming down from the mountains and on the flat going into Yakima on a section of road posted 55mph. I missed all the lights and cruised along with cruise control on at 55 for a while and got that number. I did not pump check, and haven't, but reports from TFL indicate the dash estimates are probably pretty close.

The truck has right at 20k on it with the original Michelin Energy Saver tires on it in good condition. I'd had an oil change about a thousand miles before, and had a glow plug replaced about five hundred miles before. The temperature was in the 78 to 82 deg F range. My guess is that the engine has finally broken in and that's probably the maximum I'll ever expect on the flat in perfect conditions. With a 36 gal tank that means I could hope for a plus 700 mile range if I'm going through Kansas and Nebraska, or across Texas.

Once I got out onto the highway from Yakima to Seattle and ran it up to 70 to 80 the avg dropped down close to 17, but even after coming over Snoqualmie pass into Seattle the number had come back up to about 19.7. After running about the Seattle area for a bit that was back down to around 15. Coming back yesterday eve the best I saw was a 19.7 mpg 50 mile ave even over the same 55mph stretch. This indicates again that the 24.5 was, while perhaps not a fluke, probably the maximum potential.

Typically I'll see around 15 when doing mostly mixed urban driving and around 19 to 20 out on the highway depending on speeds, terrain (and, probably, weather).

Towing I see close to 11 avg on a trip from Las Vegas to the Portland/Seattle area, with low 50 mile averages around 8.5 in the hills, and highs up to around 12.5 on the flat towing my 10k gvwr fiver.

This is not to say that I "get" 24.5 mpg! I think that is probably pretty close to the maximum you'd EVER hope to get out of this configuration. Perhaps with a SRW truck similarly equipped (mine has 3.73's, I "think" the SRW trucks have 3.42's, but am not sure) you might get a bit higher as a maximum extreme, but doubt the urban or towing numbers would be significantly higher.

Also, I drive like an old lady. If you enjoy the torque a lot obviously your mpg is going to be lower, although the truck may like it better.

The dash estimate is just that. As I said, the TFL report and other numbers I've seen at Duramax Forum indicate the dash estimates are within perhaps five percent or so, which would mean that you "might" get a maximum of perhaps 23 to 25 mpg on a 50 mile avg running at 55 to 60 on the flat in good conditions. Towing is so dependent on weight and terrain it would be hard to estimate.

Keep in mind that, while the engine is essentially unchanged for 2020, the transmission is a new Allison branded (Ford and GM co-developed) 10 speed. That and improved software could be a recipe for improved numbers.

Again, this is only something I'm throwing out there for a reference point. Your mileage will definitely vary!

fyi,
Kate
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Old 08-25-2019, 08:40 PM   #2
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Very good information. Thanks for posting.

My 2012 F-450 with 4:30 gears got 15.5 mpg highway and 10mpg towing a 16,000lb 5th wheel.

TFL is really a great source for information and entertainment.
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Old 08-25-2019, 09:45 PM   #3
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Originally Posted by tuffr2 View Post
Very good information. Thanks for posting.

My 2012 F-450 with 4:30 gears got 15.5 mpg highway and 10mpg towing a 16,000lb 5th wheel.

TFL is really a great source for information and entertainment.
They are entertaining sometimes. I wish theyd test with fivers. A lot of those trucks they test are used as haulers. Ive heard people say there are several thousand pounds of air resistance on a fiver at road speeds but Im too lazy to do the math . It would be interesting to see what a truck did at 75% of GCWR towing a 13 6 x 8 1/2 foot fiver going up the Ike!

Kate
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Old 08-26-2019, 05:43 AM   #4
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The only guy I saw towing a travel trailer is BTBRV. He towed one of those 38' travel trailers with his dually truck on a windy day and said it towed fine. No sway with his dually.

I agree that TFL is towing trailers that do not have much wind resistance. My rig would get a little as 9mpg towing into the wind and 11 mpg towing with the wind. I could tell driving also. It is a lot more tiring driving into the wind and it is easy to tow with the wind.

I have started watching some of 'Danger Industries' videos to see the abuse he puts his trucks through. He is a Hot Shot trucker and does not care about weight limits and is in Canada. He is a likeable enough guy I think.
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Old 08-26-2019, 07:12 AM   #5
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My husband watched a lot of you tube videos comparing the big three diesel dually trucks, before settling on a 2019 GMC Sierra 3500 dually. He's a licensed HDM and motor mechanic since the dawn of time. All videos were were of the trucks pulling the same load up the same stretch of highway somewhere in the US
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Old 08-26-2019, 07:45 AM   #6
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The Duramax 910 ft lbs or torque matches the Ram's 1,000 ft lbs of torque. I have seen the 3 trucks on a dyno. The GM truck actually beats both Ram and Ford at putting power to the ground.

The Duramax is very impressive indeed.
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Old 08-26-2019, 09:58 AM   #7
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I do not think that fuel mileage is that impressive for a new diesel truck, that use DEF. My 2008, Mega Cab Dodge with the 6.7L Cummins and a 6 speed 68RFE transmission with 3:73 gears and without the use of DEF is averaging 11 MPG towing a 13,000 pound 13'-6" 5er. In the mountains I normally get between 8.5 to 9.5 MPG. This was on I70 the last time I went through the Eisenhower Tunnel. This is all hand calculated fuel mileage.
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Old 08-26-2019, 10:14 AM   #8
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Horse power and torque in the combination of miles per gallon with DEF, EGR, SCR, DPF etc is, yes indeed impressive.
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Old 08-26-2019, 05:48 PM   #9
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Quote:
Originally Posted by Elisavaet View Post
I thought I'd post some fuel economy numbers for my 2019 Chevrolet High Country crew cab 4x4 dually with the Duramax diesel and Allison transmission. I'm just doing this so that anyone considering the new diesel (L5P since 2017, and continuing with only cooling system changes primarily into 2020) will have a basis for reference if they are interested.

The dash on the Chevy shows a 50 mile avg fuel economy number. That's been at 22.7 for a long time. On a trip yesterday from The Dalles, OR to Seattle, WA I managed to push that number up to 24.5 after coming down from the mountains and on the flat going into Yakima on a section of road posted 55mph. I missed all the lights and cruised along with cruise control on at 55 for a while and got that number. I did not pump check, and haven't, but reports from TFL indicate the dash estimates are probably pretty close.

The truck has right at 20k on it with the original Michelin Energy Saver tires on it in good condition. I'd had an oil change about a thousand miles before, and had a glow plug replaced about five hundred miles before. The temperature was in the 78 to 82 deg F range. My guess is that the engine has finally broken in and that's probably the maximum I'll ever expect on the flat in perfect conditions. With a 36 gal tank that means I could hope for a plus 700 mile range if I'm going through Kansas and Nebraska, or across Texas.

Once I got out onto the highway from Yakima to Seattle and ran it up to 70 to 80 the avg dropped down close to 17, but even after coming over Snoqualmie pass into Seattle the number had come back up to about 19.7. After running about the Seattle area for a bit that was back down to around 15. Coming back yesterday eve the best I saw was a 19.7 mpg 50 mile ave even over the same 55mph stretch. This indicates again that the 24.5 was, while perhaps not a fluke, probably the maximum potential.

Typically I'll see around 15 when doing mostly mixed urban driving and around 19 to 20 out on the highway depending on speeds, terrain (and, probably, weather).

Towing I see close to 11 avg on a trip from Las Vegas to the Portland/Seattle area, with low 50 mile averages around 8.5 in the hills, and highs up to around 12.5 on the flat towing my 10k gvwr fiver.

This is not to say that I "get" 24.5 mpg! I think that is probably pretty close to the maximum you'd EVER hope to get out of this configuration. Perhaps with a SRW truck similarly equipped (mine has 3.73's, I "think" the SRW trucks have 3.42's, but am not sure) you might get a bit higher as a maximum extreme, but doubt the urban or towing numbers would be significantly higher.

Also, I drive like an old lady. If you enjoy the torque a lot obviously your mpg is going to be lower, although the truck may like it better.

The dash estimate is just that. As I said, the TFL report and other numbers I've seen at Duramax Forum indicate the dash estimates are within perhaps five percent or so, which would mean that you "might" get a maximum of perhaps 23 to 25 mpg on a 50 mile avg running at 55 to 60 on the flat in good conditions. Towing is so dependent on weight and terrain it would be hard to estimate.

Keep in mind that, while the engine is essentially unchanged for 2020, the transmission is a new Allison branded (Ford and GM co-developed) 10 speed. That and improved software could be a recipe for improved numbers.

Again, this is only something I'm throwing out there for a reference point. Your mileage will definitely vary!

fyi,
Kate
Thank you for that information Kate! Your truck is the model I'm looking at when I eventually replace my gas dually. Are your towing numbers hauling the rig you have in your signature? If so, does 7500 lbs dry, 10 000 GVWR sound about correct?

I just returned from 3 weeks of very mountainous driving hauling 13k. My rig was taxed but got the job done yet again, albeit sometimes at lower speeds than I'd like.

For sure a turbodiesel rig like yours would be optimal for the long hauls we are planning at retirement. Your injector and other issues trouble me though. I have a few years for them to iron out the bugs.
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Old 08-27-2019, 06:08 AM   #10
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I have a 2018 GMC 2500 dsl and usually average right at 20 empty. Mileage drops to around 11 when pulling anything. Truck has been trouble free and has 30k mi on it.
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Old 08-27-2019, 08:02 AM   #11
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Thank you for that information Kate! Your truck is the model I'm looking at when I eventually replace my gas dually. Are your towing numbers hauling the rig you have in your signature? If so, does 7500 lbs dry, 10 000 GVWR sound about correct?

I just returned from 3 weeks of very mountainous driving hauling 13k. My rig was taxed but got the job done yet again, albeit sometimes at lower speeds than I'd like.

For sure a turbodiesel rig like yours would be optimal for the long hauls we are planning at retirement. Your injector and other issues trouble me though. I have a few years for them to iron out the bugs.
Yes, the towing information was towing that 2011 Jayco. I haven't run it across a CAT scale but it's 10k gvwr. I'd guess 9k actual at least.

I've found the truck to be comfortable both in daily use and for long hauls. My longest day was 14 hours coming from Vegas up into S ID. That was TOO long and I got pretty tired the last hour or so. I was trying to get to the W side of Boise so I wouldn't have to deal with traffic in the morning, but I'd NEVER have been do anything close to that in my old 2002 3/4 ton Dodge with the Cummins. The Duramax dually is confidence inspiring and I've towed through mountains with snow on the grain, rain, wind, and heat.

K
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Old 08-27-2019, 08:21 AM   #12
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I have a 18 Chevy DRW with 10k miles so far and no issues to report to date, except 2 oil changes. I recently got 14.1 MPG in flat NE on a windless day for 350 miles pulling a fifth wheel at 25k gross rig wt. I have also gotten 24 mpg solo and will admit that old ladies will blow past me taking off from stops.
The 18 Chevy is a great upgrade from my 06 Chevy DRW that had 315k miles with min maint ever needed on it.
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Old 08-27-2019, 08:50 AM   #13
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Horse power and torque in the combination of miles per gallon with DEF, EGR, SCR, DPF etc is, yes indeed impressive.
What I am getting at the truck is using DEF to help with the emission compliance of the EPA! Correct? Where as the early Doge/Ram trucks with the 6.7L Cummins Diesel engine from 2007.5 to 2012 does not use DEF. Instead they use diesel fuel to burn off the emission particles that the DPF collects.This will occur approximately ever 200 miles or so, and last between 15 and 20 minuets to clean the DPF when pulling. At least my truck follows this cycle.This does nothing for fuel economy since the diesel fuel is used strictly in the exhaust system to regenerate the DPF.

So, the newer Chevy/GMC trucks that are using DEF should see improved fuel mileage over the older style of emission compliance when under heavy load regardless of higher horsepower and torque. Especially since this horsepower/TQ is not developed thru the full power range but only at the top of the power curve.
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Old 08-27-2019, 10:51 AM   #14
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I averaged one of the worst fuel economy numbers this trip but it was the worst terrain I'd seen in years, similar to Newfoundland.. Up/down every 30 seconds or less, some inclines hit 22%.

I got 7.85 MPG overall for this trip over 3000+ km. I also have a bent axle on the 5th wheel causing drag. Tire is wearing like crazy on one edge and I had to rotate to avoid scrapping it.

Prior to this I had managed up to 9.6 MPG on relatively flat ground hauling the same load. Gonna see next year once I fix the axle.

A diesel rig would have gotten 2 MPG better but then the fuel is usually a bit more at the pump,depending on time of year and location. It really varied at locations on this trip. Sometimes diesel was 5% less and others it was 20 to 25% more.
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