GMC 2500HD Duramax/Allison

[Rebel702]

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.

[3 Happy Campers]

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 I’ve managed 23mpg.
Towing my 12000lb 5er & again staying @ 60 mph I’m 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 I’m run @ 16mpg overall average.
This is just a weekend driver towing the 5er or when I have to go to Home Depot & don’t want to be seen driving the minivan.

[M109Rrider]

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.

[acadianbob]

Originally Posted by M109Rrider

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.

[3 Happy Campers]

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.

[bsmall]

Originally Posted by 3 Happy Campers

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...

[TURBS]

Mine is within 1 mpg and one gallon of fuel usage.
Not sure how that's an overly optimistic figure

[M109Rrider]

That's great. Mine are 2-4 off

[wakamicamper]

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.

[Rebel702]

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.)

[flyrotor]

Originally Posted by Rebel702

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.)

Background - 2011 Dodge 6.7 Cummins, 6 speed manual transmission, Crew Cab, Long Bed, Trailer is Wildwood 25BHLE (GVWR 7680, 26ft)

1. Yes I use my cruise control towing when conditions permit, which with my setup is most the time. Exceptions - winding roads, mountain highways, grades. I feel I have better control without it in those conditions, this includes being able to brake for critters who appear on the roadway,

2. I use the exhaust brake most the time, towing or not, with the manual transmission it is amazing how great it works, even with daily commutes. I don't think it has any factor on the gas mileage as it only engages when the your foot is off the accelerator. While towing, I can descend most grades without touching the brakes while even passenger cars and SUV's (not towing) are riding their brakes. I would never want to go without it again!

[wakamicamper]

Someone mentioned a spreadsheet for calculating, and I have been using one for my last 2 trucks from this site:

FordF150.net Downloads - Backgrounds, Screensaver, and more

The spreadsheet are in Excel and are free to download, it gives you measurements in both US and Metric. I use the metric, because Canada in using metric, but it also converts back to mpg for us old folks who are having trouble learning metric.
Anyway, this is an excellant spreadsheet.

[Coops1]

Originally Posted by Rebel702

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

I've been using an iPhone app to do all of my calculations since I bought the truck and my numbers are right in line with yours for overall average.

[RubenZ]

Keep in mind if you increased tire size from the factory itty bitty pizza cutters that GM puts your MPG on the computer will be off. You need to use a programmer to let teh computer know the new tire size.

[MIKE44460]

I reset my computer before my trips, Canton OH to Myrtle Beach + or - 640 miles , driving around 60-65 I can get close to 12, hauling ***** and I'm in the 10's. No trailer, computer reset is right up to +22. 31 foot Flagstaff classic TT, 2011 Duramax crew cab, just under 17K gross.