LMM Fuel Economy

[axisrobotics]

I have a new 2007 GMC 2500HD duramax diesel. With 3 tanks of gas and 1,127 miles on the odometer, the computer shows 18.1 mpg. I have manually calculated it to 17.86 mpg.

Mostly short 20 mile runs with some daily city traffic and aprox 125 miles pulling a 3,000# trailer.

[diegojp]

So what's the secret to all this amazing mileage I am reading about? I am on my 4th tank of fuel and average about 13 mpg city/highway. I drive about 65 on the freeway and my driving is pretty evenly split between city and highway.
Granted I have the 4x4 and usually have to drive with the AC on but I can't imagine those factors make a huge difference. Am I missing something? TIA

[Albee]

06 LLY 4X4 Dooley. Best seen on freeway ever is 16.3. Around town, 12-13 mpg. Pulling 17-18K over hill and dale 8-9 mpg. Not as good as my 02 LB7 2500HD. Best was just over 20 hwy. and got around 15-16 in town. This LLY is not near as economical. But she runs good.

[axisrobotics]

The best I can tell the dual zone a/c stays on all the time. I get about 1.1-1.3 better mileage with the compressor button turned off.

[winmck]

3 tanks - mostly highway - averaging 16.5 mpg on the DIC

[Sivrug2]

Hi, I am new to forum

I purchased an 2007 LMM six weeks ago and mileage is as 5780 miles-404.1 gal. 14.3 manual calculation DIC says 14.7. I drive mostly highway unloaded and drive like an old granny. 60-65 MPH. Needless to say I am not happy with mileage. I have had diesel PU's since GMC started with the 5.7 and have had Fords, Dodges and GMC's.The Dodge was a fairly good truck but the dealer was very bad so no more Dodges. Currently in my business I have 4 diesels 2001 GMC 2004.5 GMC, 2005 F350 6.0 Powerjoke and the latest 2007.5 and this one is currently the least efficient.
I have the Bully Dog Pup on my desk right now and need to download. I am hoping that this will give me a couple MPG.

[SDWA]

All this talk makes me want to keep my 2002 LB7, no matter what it costs to keep it running! I've consistently gotten 18-19 mpg from day one, peaked at 21 in the first year, on a full-to-empty flat road trip...

Scott

[diegojp]

Just thought I would post an update. I did a 5 day offroading trip last week and averaged 9 MPG(DIC and calculated) towing over 14,000# on freeways an mountain roads. Not too shabby, IMO.
Unloaded my truck is still pretty consistantly getting just over 13 MPG with mostly city(60%) driving. Unloaded on the freeway today, I was able to get 19 MPG over about 100 miles at 69 MPH. That dropped down to 14.5 shotrly after I got off the freeway, however.

[jharden1]

17.6 DIC on the last 1600 miles. Mixed miles. 7500 miles on the truck.

[craigth]

I am VERY unhapp with my LMM 2008 GMC 2500HD Crewcab SWB 4WD gas mileage!! My '02 of the same model got 100 miles to the tank better than the '08! I'm really surprised that 6 model years later and with the fuel price/supply issues that GM could not at least maintain the mileage of my '02 or make it better! I wonder if a power programmer would help?!?!

[Stlheadake]

Craig, I would be careful putting a programmer in that truck. From what I understand, you run the risk of clogging the DPF with a programmer. Not a cheap fix for more mileage.

I too have been in the 'hunt' for better mileage. My '06 doesn't do too bad 15 city and as high as 18-19 hwy (about 70mph). Still I feel it could/should do better.

[RaiderCoach]

I purchased an LMM crew cab 4wd in May. The fuel economy was never better than 16 mpg hwy and 13 hwy city. I lifted the truck and put 33" tires on it and hoped that it was a break in issue. My previous truck, an 03 duramax, would average 15 mpg city and up to 22 mpg hwy empty and 14 - 17 mpg hwy towing, varied depending on weight of load from 7000 to 12,000 lbs. I had an edge juice programmer on that truck. I recently put a Bully Dog Power Pup on this truck, really hoping for some mpg results. Being able to correct the speedo was nice, the truck didn't really need that much more power. No matter what the setting that I have the Bully Dog set to, I am averaging right at 13 mpg in town and 17 hwy. I have a very light right foot, so unless milage would increase with a heavy foot, I am probably at about where I'm going to be. Currently the truck has 9400 miles on it. I really miss my 03 and wish I had stayed with it.

[craigth]

I lifted my truck with a ProComp 6" and 34" tires in Sept '07. You can see pictures in the TDP Photo Album page.

Interesting that you were able to adjust the speedo as the local GMC dealer said it couldn't be one with Allison transmissions! They also said that I couldn't have the tire pressure sensor set lower than 62PSI. However, a friend of mine with an '08 LMM 3500 said his dealership awas able to lower it in the 50PSI range. Not real happy with the knowledge and willingness to service non-standard features at the dealership.

Was the tuner worth it for performance? Did it make any noticable difference? Why did you select the Bully Dog tuner over another brand?

I wonder if GM knows about the LMM MPG issue?! I also wonder if this forum and the members of the TDP could use their numbers to communicate the issue and see if GM can tell us why and/or address the problem with some modifications.

It's really sad that in this time of high gas prices and diesel technology promoted as high mileage GM can't at least maintain or better yet increase the MPG of their LMM trucks. Most vehicles from year to year increase their MPG not decrease.

Maybe GM will get the wake up call they need when Toyota producesa 2500/3500 series of trucks with their own diesel! I'm sure their MPG will be high and more than likely the truck features and quality will be superior!

[RaiderCoach]

I went with the Bully Dog because the sales manager at the dealership that I use recommended it. My previous tuner, in my 03, was an Edge Juice. It worked really well, but I did have some stalling problems so I decided to try this one. The Bully Dog does allow you to tune the speedo to your tire size, although I have not checked it to make sure that it really did anything. There is definetely a power difference, although for street driving without a load, I don't really feel that there's a need for the increase. I netted about 1 mpg increase, far below the 3 mpg increase that I realized with my 03 and the Edge product. I would not recommend spending the $500 for that small of an increase. I'll be taking my truck in for it's 10k oil change soon and will talk to the service manager about the milage issue, although I know the answer already that I'll get. It will be "We're not aware of anything wrong"? Always the same answer, until GM sends out a bulletin in about 6 months...

[Nolafishr]

I am getting 17.8 MPG on mine, I topped off yesterday at half tank, I had 245 miles on the trip meter and it took 13.7 gals to top it off and I hand calculated the mileage and this is what I got. I did not check it against the DIC, Truck has 400 miles on it so far and still breaking in. I usually fill at half tank because it is a lil easier on the pocket at times, Diesel is at $3.24 a gallon here. I had it on the Highway with most of the mileage before I topped it off to see what it would do. I will keep a check on the Fuel mileage on it, so far I am happy with it.

[Runaway_Dmax]

Hmmm...you guys posting on this site don't seem to have the luck/mpgs that the folks have over at the other site (DP) get..

I hope they are closer to what to expect than what I see here or I will be sadly disappointed in the new truck.

[Dakster]

Here's what I have noticed. Each boards mileage claims vary as much (or more) than the mileage I actually get with my own truck. My normal everyday driving I get lousy mileage. Although, I take a lot of short trips and even my longer ones as on So. Florida parking lots (highways). The heat and being at or under sea level doesn't help either. (Doesn't make sense to me, but I get MUCH better fuel economy once I hit the rolling hills of GA and it stays that way until I get back home from Connecticut or in last years case Tennessee)

Obviously the LMM gets worse mileage than its predecessors, and from what I have expereinced and read it has a lot more power, and a restrictive exhaust too. The best case people seem to say about 1 mpg less and others up to 5-6 mpg less. My LMM gets better MPG than my gas 2007 6.0 Suburban (4x4) and 2005 Denali XL (AWD) and about the same as my 2005 Ford F250, 6.0 DIESEL, 4x4, CC, SB. Which is around 12 in local driving in town and 14-15 on highwy drives, but I drive fast 75-80. And yes, I wish I got better MPG's, but don't we all?

[snowsporter]

I had just purchased a dmax with the lmm engine. at just over 60 mph i am averaging almost 23 mpg highway. combination so far i am averaging around 17 mpg. first diesel and so far am impressed. i had just traded an 8.1 for the dmax that averaged highway 8 mpg, city around 6 mpg and towing 10k trailer 5mpg.

[kwtriton]

Purchased an.. 07 NBS 4x4 4dr. short bed. Traded 01 xt-cab 4x4 D-Max w/300,000. The 01 constantly got 19 mpg on the hwy, New 07 is kind of strange and I am sure it has to do with the power curve. At 65 mph reset avg mpg truck gets about 16.5 mpg. run it up to 75 mph truck gets 21.8 to 22 mpg. I thought it was a fluke, but I have checked it several times and get the same results. Avg overall it has been running around 17.8 to 18.2 mpg, Truck now has 10,000 (+) and I am very satiisfied w/mpg.

[craigth]

How are you calculating your MPG? Using the onboard ECU calculations or actual miles driven / gallons of fuel used? To be honest I don't trust the ECU calculations.

You definitely the exception to the rule. I'm still getting 10-11 MPG City / 13-14 Hwy, if I'm lucky. A friend of mine also has an '08 Chevy 3500 Crew LWB 4x4 that gets similar gas mileage to mine.

I would definitely like to know what the difference is and the secret to obtaining higher gas mileage. As I mentioned previously my '02 got MUCH BETTER MPG and I should of held onto it!