for those with thirty K miles or more, fuel milage numbers

[James S]

Hey Folks,

You all seem to be getting that milage spread sheet. Acording to that article in the ford-diesel web site, fuel milage should start to remain constant at about twenty thousand to thirty-thousand miles of driving. For those of you that have trucks with twenty-thousand miles or more on your rigs, what kinds of milage are you getting in town and on the highway. I ask all these questions, as I am about to purchase a 2003 GMC CC longbox. I would like numbers for those of you with the Allison and ZF 6 speed. This will aid in helping me decide on which transmission to get. [I like both, but do not know about milage differences.] Thanks for this.

James

[KompressorMan]

James,
In the beginning, while the engine is "tight" you can expect 15-16 MPG. Then after about 20K, the milage will ease up a couple of points. My truck has 35,000 now and I was getting about 17 to 18. Now, as a by note, I've just sent my truck from N.E. Georgia to Bozeman Montanna pulling a 28'enclosed trailer with a relatively light cargo load. The driver reported back today that milage is about 8. I'm shocked, then I found out the S.E.S. light came on coming back through Kansas City. He stopped at Highfall GMC (wonderful service) and found that the #3 injector had fouled. They didn't have one on the shelf, but told him that the truck would be ok to drive back, since there didn't seem to be much of a loss of power. Just a light smoke. You will love the truck smile.gif

[James S]

Hey Kompressor Man,

Is that seventeen or eighteen in town??? For everyone to note, I am getting a 2500, not a 3500, so if milage is impacted, please only give me numbers for 2500 models, and please emphasize milage for in town, AND on the highway.

Thanks for this.
James

[spctr13]

Here is about as accurate a mpg as you can get : I have a 98 gallon aux. tank , so only fill after a lot of miles . As you can see by my signture it is a 2001 , 2500, ZF-6 , and when filled to capacity runs about 8600#s @ 52,000 miles .
Last month ,June, after arriving in Wisconsin ,filled both tanks ,topped to overflowing , put on 900+ miles , mostly rural 55-65 , no more then 150 interstate @ 65-75 . averaged 20.8 mpg .
Filled again , same procedure , returned to Massachusetts 95% interstate @ 70-75 ,through Chicago at noon , 1130 miles averaged 18.47 mpg .
Also last summer pulling a 26ft travel trailer to Alaska and return averaged 12 mpg , fairly new truck at the time . Last month pulling same trailer from Mass. to Wis. all interstate 72mph ,got 13 mpg .

Hope this helps
Mac

[DucksnDiesel]

Well I rolled over 17,000 miles last week in my 2500 and so far, I get consistantly between 17 and 18.5 mpg in town (has been as low as 16, as high as 19 depending upon traffic and how I drive it). On the highway, I get between 19 and 21 mpg depending upon how hard I push it. I have tracked the mileage for every tank. I haven't really towed anything yet.

[86gmc]

At what highway speed do the Duramax/Allison obtain the most fuel mileage, I'm guessing 62 to 65 mph?

[DucksnDiesel]

I have been consistanly getting about 20-21 mpg while running on cruise (with the AC on) at around 70+ on the highway. I don't want to slow down to see if the mileage would be better at 62.

[Idle_Chatter]

My 2001 2500 got 19.5 mpg on the interstate "right out of the box" because I drove it from Wisconsin to San Antonio and back a week after I bought it. It also dropped to about 16 mpg while I was in San Antonio driving stop-and-go. It settled-in to high 16's to mid-17's in town and high 18's to mid 19's on the highway for about the next 20,000 miles. All of a sudden without warning my stop-and-go commuting up here in Md/Pa jumpe up to the high 19's!! With over 27,000 on the clock now, I'm getting 19.5 to 19.8 driving my daily commute. I haven't driven any real interstate since March, so I can't really assess what my new highway miles might be. I towed about 6,000 pounds from Wisconsin to Florida at a steady 70-75 and got low 15's. I towed about 4,000 pounds from Florida up to Maryland and had to take two-lane backroads most of the way. Running County roads at 45-50 mph with that load on I got 17.4!! I think these trucks run *really* efficiently in the 50-60 mph band - it's just hard to keep 'em down there! :D

[richp]

I've tracked fuel economy on my 2001 D/A since day one using a spreadsheet.

It's hard to detect patterns since many of my tanks reflect a mix of highway, city, and towing. However, I've seen as much as 22.75 mpg unloaded and as little as 7.8 towing my 27' fifth wheel into a headwind up to and into the Rockies. Looking at the sheet as a whole, about 18 mpg seems to be my unloaded average, with 11-12 when towing.

I sometimes wonder about pump accuracy or fuel quality (from the last fuel stop) when I get a fillup that is out of line with the rest of the trip. And as always, head and tail winds and temperatures make a difference. Last time I towed the fiver over the Rockies, for instance, I got 19.5 mpg between Grand Junction and Denver. It could have been cool temperatures, tailwinds, and a lot of downhill coasting (don't you love that tow/haul??!!). But I also know I was doing the speed limit plus 4 everywhere it was prudent, so numbers like that make you wonder.

However, taking all of that into account, my overall mpg performance for the first 32k miles has been 13.5 mpg, with about 2/3 of the miles towing.

Rich Phillips
Member #28