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Old 11-28-2016, 12:01 AM   #1
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2013-2014 6.6L Duramax Fuel Economy

I hear people claiming a factory 18 to 20 mpg (with no load) with the 6.6L Duramax trucks.

I get 13.5mpg unloaded on the highway with my 2014 Silverado 2500HD running the 6.6 Duramax Diesel. I have a hunch that the older models get better fuel economy than the newer ones so I am reaching out to ask anyone that has a 2013 or 2014 6.6 LML Duramax to ask what is your fuel economy.

I am trying to find out if it is possible to get the 18 to 20 MPG like I know others are getting. I know this type of discussion opens a can of worms with people suggesting modifications but I am interested in why some people get great fuel economy with a stock setup and some do not.

Thanks for your input.
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Old 11-28-2016, 12:12 AM   #2
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I have a 2016 GMC Denali 1 ton Duramax and getting between 21 and 22 MPG on relatively flat interstate at 68 miles per hour. I have not towed with yet since less than 500 miles on it. No why your mileage empty would be in the 13's even running 75 it still should be in the 17 to 19 range.
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Old 11-28-2016, 09:17 AM   #3
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Unhappy high milage

If you are using your DIC to report milage then you are wrong. For 25,000 miles I have compared what the DIC says and the fuel used is always lower than what is actually pumped into the tank. The mpg is always 3 mpg higher than what the hand computed mpg is. I do not know if the computer can be reflased to correct the discrepancy or not. I do not know when they program the computer if they take into account tire size or not....
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Old 11-28-2016, 09:49 AM   #4
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The only true way to know is by good ole math calculation. Too many report what they see on their DIC...do the math then report. Too many DIC's give an average as well as an instant reading. I think some people report their instant reading while coasting downhill!
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Old 11-28-2016, 12:34 PM   #5
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Have a '16 Z71 LT. I get about 21-22 on the highway at 70 unloaded(setting the average to last 25 miles). Mixed driving around town comes out around 15.5. About 10.5 towing at 70. That's on the computer, so may very a little if I do the math, but experience has shown little variance. Much better than my gasser. Not really why I bought it, but I do like that I get a hair more range towing than with the gas model.
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Old 11-28-2016, 01:07 PM   #6
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Thanks Bob and WFD,
I am calculating by hand

CWS and Phenom your engines should be identical to mine. This is encouraging. I just bought this truck a few weeks ago and it has 99k miles. I will check everything over and look for a reason for the poor mpg.

Thanks
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Old 11-28-2016, 01:22 PM   #7
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I don't know about a Duramax but my 2015 RAM 2500HD CrewCab 4x4 with 6.7 Cummins got 21-22 mpg @ app 70-75 MPH over 5 days and 1000+ miles

Truck was loaded with 4 adults, 1 toddler (with car seat), 2 large Dogs, 1 small dog and assorted luggage that 3 three women haul around for a 1 week trip.

I was shocked!
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Old 11-28-2016, 02:03 PM   #8
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2015 1 ton, chevy. srw
I have achieved 21mpg, empty, flat and level. but mostly its more like 17.
10-12 towing.
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Old 11-28-2016, 02:03 PM   #9
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Quote:
Originally Posted by WFD View Post
The only true way to know is by good ole math calculation. Too many report what they see on their DIC...do the math then report. Too many DIC's give an average as well as an instant reading. I think some people report their instant reading while coasting downhill!
Exactly. Fill it, record the mileage from the odometer, fill it again and take the mileage from the odometer and divide it into the gallons put in. Thats the average mpg. Not what the display says....

I get 18.5 from my hopped up 7.3 Ford.
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Old 11-28-2016, 02:06 PM   #10
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Actually you have it the other way around. The newer Duramax 6.6L gets better mileage than the older models. I traded a '07 2500 for a '16 3500 and the guys above are correct 20-22 mph on my new 3500.
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Old 11-28-2016, 02:18 PM   #11
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Duramax fuel economy

I have a 2014 1ton duramax, and I get 20mpg on flat open road, 18.5 on hills. I have a S&B air intake and I use a fuel additive. If I don't use the fuel additive I get 1 mpg less. When the truck goes into regen you can see the mileage drop. My DCI is very close to actual mileage.
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Old 11-28-2016, 02:28 PM   #12
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2015 2500 towing a 10K fifth wheel. 11.5 at 70mph -13.5 at 64
Empty 24 at 62 and 19-20 at 70
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Old 11-28-2016, 02:29 PM   #13
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I'm getting around 20 -21 mpg going 65-70 anywhere 9.9 (worst) to 12.7 (best) pulling a 35ik with my 2016 3500 srw.
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Old 11-28-2016, 02:30 PM   #14
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Oops average city/hwy 16-17.5
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Old 11-28-2016, 02:42 PM   #15
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I have 2014 Denali crew cab 2500 HD and get 18 - 20 mpg or so depending on terrain has 50k miles on it
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Old 11-28-2016, 03:01 PM   #16
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We have just about 85,000 miles on our 2008 Silverado 2500HD with 6.6 Duramax. On a recent cross-country trip, no trailer, 75 mph cruise we got about 18 mpg. Return trip, towing a U-Haul, 65-70 mph cruise, we got around 16 mpg. Towing our new 12,500 pound fifth wheel, we get a low of 10.5 mpg in the mountains, and around 13 mpg flat, level 60 mph cruise. Average mpg has been steadily improving since new.
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Old 11-28-2016, 03:03 PM   #17
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It all depends on your gear ratio. people running 3:55 versus people who are running 4:10 will see dramatic difference in their mileage.
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Old 11-28-2016, 03:17 PM   #18
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we are talking about a duramax that is only the 3.73. Your information is nice to heard.


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Old 11-28-2016, 03:18 PM   #19
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Remember to reset your m.p.g. on dic frequently or your just fooling yourself
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Old 11-28-2016, 03:31 PM   #20
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I have a 2013 # 3500 and i get 22 mph on flat road doing 70
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