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Old 02-18-2012, 02:30 AM   #1
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GMC 2500HD Duramax/Allison

Just got back from a roadtrip from Las Vegas to Salt Lake City. We did not take the trailer for this trip since snow was in the forecast. Just turned 10K miles and I have been waiting for the mpg to improve. Cruised at 75 both directions. Results: 17.7 mpg to SLC, 20.1 mpg coming back.

Now if I can get better than 13mpg dragging the TT. Won't be doing 75 though.
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Old 02-18-2012, 10:43 AM   #2
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I have the Silverado 2011 2500HD & when on the open highway not towing if I keep it @ 60mph with cruise control on & stay in the right lane Iíve managed 23mpg.
Towing my 12000lb 5er & again staying @ 60 mph Iím seeing 17-18mpg.

This is awesome compared to the 1990 Dodge 2500 V10 I had last where on a trip to FL I was averaging 8mpg towing the 5er.
According to the OnStar monthly report Iím run @ 16mpg overall average.
This is just a weekend driver towing the 5er or when I have to go to Home Depot & donít want to be seen driving the minivan.
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Old 02-18-2012, 10:53 AM   #3
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Not to be a Debbie Downer but those computer MPG guesstimators on diesel trucks have a tendacy to be very optimistic. If you hand calculate you may be dissapointed.... I know I was.
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Old 02-18-2012, 10:55 AM   #4
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Quote:
Originally Posted by M109Rrider View Post
Not to be a Debbie Downer but those computer MPG guesstimators on diesel trucks have a tendacy to be very optimistic. If you hand calculate you may be dissapointed.... I know I was.
This is often true; and usually they are optimistic.

But even if these readings are a bit optimistic, those are nice numbers.
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Old 02-18-2012, 11:06 AM   #5
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One of the first things I did after the brake in period was to run hand calculations several times.
Much to my surprise they were spot on.
I did find a three mph difference in the speedometer verses the GPS.

I expect the mpg calculations the computer does will eventually not be acurate as the truck ages.
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Old 02-18-2012, 11:32 AM   #6
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Originally Posted by 3 Happy Campers View Post
One of the first things I did after the brake in period was to run hand calculations several times.
Much to my surprise they were spot on.
I did find a three mph difference in the speedometer verses the GPS.

I expect the mpg calculations the computer does will eventually not be acurate as the truck ages.
My 2008 was nearly the same between the onboard computer and doing hand calculations also.

I run between 9-11 mpg while towing my 5th wheel, and 17-21 mpg solo on the open road...
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Old 02-18-2012, 11:41 AM   #7
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Mine is within 1 mpg and one gallon of fuel usage.
Not sure how that's an overly optimistic figure
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Old 02-18-2012, 12:13 PM   #8
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That's great. Mine are 2-4 off
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Old 02-18-2012, 01:59 PM   #9
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I have a 2009 and mine gets 24 on the hwy without my 5th and when towing 15 - 17 mpg. I have found that the mpg improves if I keep below 65 mph.

This is my first diesel and it has so far outperformed the gas truck I had just towing a tent trailer.

Winter driving is butal, in the city 14 mpg, but take it on the highway and the numbers improve to +20. I also installed a 52 gal Titan Tank to give me more distance. I usually fill once every 2 months.
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Old 02-18-2012, 06:17 PM   #10
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Accountant by trade so I am pretty anal about keeping a spreadsheet. I am right at 30 fill-ups with an average 14.3mpg calculated to the computer's 14.42mpg. Worst mileage was 8.1 over my trip from MO to Las Vegas w/ the TT and fighting 35 to 50 mph headwinds.
On the trip back from SLC cruising at 75 and I still had guys riding my bumper! (edit:to clarify not while towing)

Two follow-up questions:
1. Do you use cruise control when towing?
2. How often do you use the engine braking (for the diesel owners)? Does this help or hinder mpg? (I know it does help save the brakes. I used engine braking coming down out of Flagstaff with the TT and it was a nicely controlled ride and worked great with the cruise.)
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