LMM Fuel Economy [Archive] - TheDieselPage.com Forums

More Power

04-11-2007, 22:20

I visited the local GMC dealer today and discussed the first LMM 2500HD crew cab they sold a week or so ago. I had hoped to shoot some photos of that one, but missed it. However, I did get some shots today of an LMM equipped 3500HD chassis cab... :)

The owner of the LMM 2500 reported that his first tank of fuel produced 17 mpg while running at Interstate speed across Montana. This owner has owned a number of Duramax powered trucks prior to this one, his LB7's would produce close to 20 on the same trip, and his last Duramax (a 2005 LLY) struggled to produce 15. So, he's happy with the LMM... so far... :)

Jim

D_R_C

04-12-2007, 16:42

More Power

04-13-2007, 11:58

Here's a shot of the 2007 LMM equipped chassis cab.

http://www.thedieselpageforums.com/photopost/data/500/2007emissions02.jpg

GVW is reported as being 12K. This one is equipped with dual fuel tanks and 4WD. The exhaust system is equipped with a DOC (Diesel Oxidation Converter) and DPF (Diesel Particulate Filter), but no muffler. Also, the air mixing exhaust tip is a downturn tip ahead of the rear axle.

http://www.thedieselpageforums.com/photopost/data/500/2007emissions05.jpg

The engine looks very much like the outgoing LBZ, except there is now a throttle valve in the intake plenum, upstream of the intake air heater.

Jim

DieselMonk

04-14-2007, 04:35

[QUOTE=The engine looks very much like the outgoing LBZ, except there is now a throttle valve in the intake plenum, upstream of the intake air heater.

Jim[/QUOTE]

I am trying to compare it to my late production LBZ (12/06). Could you make either a better picture or circle that "throttle valve" please? Ran in the garage this morning and took couple of pictures of my engine compartment to compare it to your pic.
The only thing that is missing on mine is that silver shielded cable thats fastened along the firewall behind the plastic 6.6L cover.

More Power

04-14-2007, 21:10

GM calls it an "Air Intake Valve", which is controlled by the ECM. The valve is activated during DOC/DPF regeneration, EGR operation and "rich idle".
http://www.thedieselpageforums.com/photopost/data/500/2007emissions06.jpg

Jim

Duramaster

04-17-2007, 22:00

What did you think of that downturn pipe just ahead of the rear differential?:o

The C-4500/ C-5500 trucks are the same way. Looks kind of scary!

DmaxMaverick

04-18-2007, 00:47

What did you think of that downturn pipe just ahead of the rear differential?:o

The C-4500/ C-5500 trucks are the same way. Looks kind of scary!

I think GM would rather peel up road stripes than torch pedestrians.....If it ever comes to that.

More Power

04-18-2007, 14:44

What did you think of that downturn pipe just ahead of the rear differential?:o

The C-4500/ C-5500 trucks are the same way. Looks kind of scary!

The pickups use an exhaust tip that exits under the right rear of the rear bumper. Only the chassis cabs (& medium-duty trucks apparently) get the exhaust tip ahead of the rear axle.

I'll have close-up pics of all this in an upcoming article, but the tip exit looks way too close to the right rear shock.... :eek:

Jim

jharden1

04-24-2007, 18:46

DIC average for dealer delivery was 17.4. My LLY was about the same when I first picked it up.

jsracing6

05-04-2007, 23:47

i get around 17 empty on highway and 7-9 towing 7000# 28' enclosed car trailer

Dakster

05-06-2007, 16:10

I hope to see the 17 mpg empty. I got 15 on the way home tonight from the dealer... 2007 3500 CC Diesel, 4x4 Long Bed, SRW.

jharden1

05-10-2007, 18:43

Enroute to work I reset the avg. fuel mileage on the DIC just to see what numbers would come out. 35 miles of mostly level at 70 mph. 21.3 on the DIC. :)

larryh1

05-11-2007, 07:44

9,000 miles, I have not seen anything above 14.9 - empty. 10 MPG towing 30ft trailer. I have been to dealer twice now. No help there - they have been good about it, but no help. They suggested a programer. I have installed a KN filter and superchip, runing in safe tow. I was told safe tow will offer the best mileage. No change. I checked tire pressure, all is good. I love this truck but fuel prices are going to make me park it.
(I'm not comparing, but my son has the Ford 7.3 we just drove to NM. About 950 miles - towing a small trailer about 1,000 lbs. Got 29 MPG!!! I wouldn't have belived it if I didn't see it with my own eyes!!!)

Any suggestions would be greatly appreciated.

thanks
Larry

Dakster

05-11-2007, 08:04

Larryh1,

So far I am on par with you.... 29 MPG on a 7.3 is incredible, that has to be a 2wd truck? I could get 22-24 with a 2wd 6.0 excursion (when it actually ran)..

larryh1

05-11-2007, 19:26

Dakster

That was doing 70 mph (cruise control), flat level driving with an occasional mountain range. I was enjoying ragging him about how much more comfortable my chevy was compared to his ford, until we figured his mpg. I kept quiet after that.

I haven't given up yet. I will be happy with 17/19 empty highway,and 11/12 towing. I am talking to a diesel shop for some less expensive ideas. I'm not going to spend thousands of dollars to get 2 mpg more. I also keep checking this board for any ideas.

Larry

Dakster

05-12-2007, 06:05

I hear you... Chevy's definetly have better comfort features... My 2007 Suburban was getting 9-10 in the city and 14-15 on the highway empty/not towing. I'll be happy with 12 in the city and 17 on the highway empty. (20% better fuel mileage). I have nowhere to go but up! I'll get a better handle on what to expect for fuel economy in two months when I drive to tennessee and back.

You can rag on the new 6.4 Ford's, they get horrific mileage. A buddy of mine traded his 2006 Dodge for a new ford (both are dually's) and gets HALF (6 mpg!) of what the dodge got while towing his car to the races. He doesn't know if he can afford the new Ford because of fuel costs! This new DPF/regen requiement doesn't seem to be very MPG friendly.

Stlheadake

05-16-2007, 19:06

I put on the Kennedy 4" turbo back pipe and saw an immediate change in mileage. I went from 15 around town to 16 and some weeks 17. I can get 19 steady on the highway running 70. If the wind is right, I have touched 20 but it is a rarity.

I too am looking to consistently get in the 20s with mine. It is a daily driver that I use to tow our camper about every other weekend.

jharden1

05-26-2007, 20:13

17.9 DIC last tank of mostly freeway. 2k miles. DIC said I used 20.7 and I put in 21.2, off about 2%.

DMAX-HD

06-15-2007, 05:45

avg 17 both hwy and city. 3rd tank of fuel

1stDiesel

07-03-2007, 19:28

I have run 3 tanks of fuel through my new 2007. It is the 2500 crewcab. I filled up today and found I got 14.6 MPG on routine and city driving. I was hoping for better, will it get better? Going camping this weekend will let you all know how that goes pulling my trailer...

axisrobotics

07-05-2007, 11:37

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

07-11-2007, 18:34

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

07-12-2007, 09:43

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

07-28-2007, 04:54

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

07-31-2007, 12:29

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

Sivrug2

08-11-2007, 08:47

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

08-15-2007, 18:06

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

08-28-2007, 16:30

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

10-09-2007, 04:45

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

craigth

10-17-2007, 23:11

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

10-19-2007, 08:54

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

10-21-2007, 19:58

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

10-22-2007, 18:53

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

10-22-2007, 20:56

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

11-19-2007, 12:26

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. :D

Runaway_Dmax

11-21-2007, 21:03

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

11-22-2007, 06:51

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

12-06-2007, 13:44

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. :D:D:D

kwtriton

12-10-2007, 13:41

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

12-11-2007, 17:36

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.:confused: 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!:mad:

RaiderCoach

12-19-2007, 17:32

I have broken the 10,000 mile mark with my 07 LMM. I have not noticed any increase in mileage yet. I average 17mpg hwy and, sadly, about 10.5 in town. This is with very light footed driving also. The 10.5 in town is with the computer set to the factory settings (Bully Dog progammer). I just filled up with my first tank of B50, I'll use B99 when the weather warms, and reset the programmer to the next power setting. Speaking with the service manager at my Chevy dealership, they have had problems with the programmers causing the dpf's to clog, so I have left mine at the stock setting. With my '03 Duramax, I ran B99 often and found that there was much less soot produced with that fuel, so I'm testing to see if the combination of the programmer and the Bio-Diesel will result in improved economy. I will report back after a month or running this scenario.

On a separate note, I find that my computer is generally off by one gallon at fill ups compared to the amount of fuel that it takes to fill the tank. I attribute this to the remote start that I use every morning to take the ice off. I don't think the computer monitors the fuel usage while in the remote start mode.

kratos1

12-21-2007, 16:04

I am trading in my 04 LBZ for an 08 LMM. Any word on programmers available for the new motor. I have 138000 on my 04 and get 17-21 mpg depending on how I drive. I installed the Hypertech programmer and ran it on stage 2 the whole time which dramatically increased power and about 2 mpg. I was talking to a guy that bought an LMM about 6 months ago and said he's getting 15-19 depending on how heavy his foot is. A friend of his bought an LMM a few months later and is gettig 13-15 mpg. Difference being he put larger tires, 305 instead of 265 and lost about 4 mpg. I guess the key is leave everything stock. Neither guy has a programmer so the trucks are bone stock. I plan on leaving everything stock on mine with the exception of the Banks programmer, larger exhaust and cold air intake. If any one has any suggestions I'll listen

DaveRuane

12-31-2007, 21:21

A friend of his bought an LMM a few months later and is gettig 13-15 mpg. Difference being he put larger tires, 305 instead of 265 and lost about 4 mpg. I guess the key is leave everything stock. Neither guy has a programmer so the trucks are bone stock.

Without a programmer, the computer cannot provide accurate miles/gallon nor speedo, nor odometer. Going from 265 to 305 should be a significant error on all 3 of these measures. I bet he actually gained mileage if he only "sees" a loss of 4mpg. Does anyone have the math on the %difference from 265 to 305? I know that going from 245 to 265 causes a 3.9% error...

dustoff_doc

01-01-2008, 19:32

I bought an 07 3500HD in November. I have 4K and DIC is 15.2 MPG. I wish I had the MPG my 04 2500HD had a trade which was over 17 MPG all the time. Oh well! I still like the power of the new 07 just wish the MPG was better!

MrBSA

01-06-2008, 18:50

I was going to post a question about my deteriorating fuel mileage but decided to jump in here and see if anyone can help. I have a 2002 2500HD Dmax (not sure what model engine that makes it) that I purchased used here in Canada with 130,000 Km. When I first got the truck I was consistantly getting around 23 to 24 MPG (Imperial) around town (some hiway, some town) and while towing the 5th wheel would get anywhere from 15 to 18 MPG depending on terrain etc. I was quite happy with those figures! I now have 144,000 Kms ot the clock and lately my around town MPG have been dropping steadily, first to about 21 and this week to 18 MPG. I convert my mileage with a calculator using the Kms travelled since previous fill up and # of litres to fill the tank. I don't think my driving has changed (not aggressive on the throttle), the truck seems to still run well, doesn't smoke that I can tell, so what's up! Any ideas what is causing the drop? As always I appreciate the comments and help.
Cheers,
Bruce
Vancouver, BC

Stlheadake

01-06-2008, 22:16

Maybe winter blend fuel? I notice that in the cold I do get worse fuel mileage. Are you using a winterfront to keep the heat up as well. I notice an increase in mileage when I use my winterfront in cold weather. The truck seems to run about 20 degrees or more warmer. I get plenty of heat, but the performance seems to be better.

MrBSA

01-07-2008, 11:19

Hi Scott,
yes I wondered about the cold weather aspect. I don't use a "winter front" ( I assume you mean something that blocks off cold air to the radiator). Maybe I should try that. It has been a little cold here at times and the truck does take a long time to warm up. I do occcasionally add a fuel additive but haven't been able to determine if it makes any difference. I would like to try bio fuel but can't seem to find a station that sells it anywhere around here. Also having trouble finding a 15/40 synthetic motor oil other than "Royal Purple" which is a staggering 7+ dollars a litre. When our trucks take 9 1/2 litres that makes for an expensive oil change!!
Cheers,
Bruce

RaiderCoach

01-13-2008, 21:43

OK, I ran two tanks of B50 (50% bio and 50% petro) in my LMM with the Bully Dog programmer set to the 'Towing / Economy' setting. Truck ran well, smelt horrible, and got worse economy than running at the stock settings with 100% petro fuel.

Even still, I'd like continue to run bio fuel...seems like the right thing to do. I don't know why the smell from the exhaust is so rancid though, on my previous '03 Duramax, it smelt like french fries or something, but on this truck with the advanced emission controls, it has a very acrid, harmful smell. Anybody have any insight to this? I'd hate to be running a fuel that's going to cause me to get cancer or something!

I did notice that speed has a very large part on the fuel economy on this truck. Unlike my '03, that seemed to get better mileage as you increased from 55 up to 75 mph, this truck goes the other way. At 55 mph I peaked with my trailer at about 13.5 mpg and at 65 I was at 8.5 mpg. Didn't even try 75 as I may not have had enough fuel capacity to make it to the next filling station:)!

Canuck76

05-14-2008, 15:32

I have a 2007 LMM on a 2500HD that doubles as a daily driver (no load). I have yet to get less than 15 MPG combined (DIC) roughly half city half highway after 18500 miles. Seems like the magic highway speed is 55 to 60 mph. I have scored as high as 23 MPG pegged on 60 mph (DIC).

Sivrug2

05-15-2008, 18:45

Raider,
I would not exceed 20% bio in the LLM. When the LLM goes into regen the bio will cause problems. First the regen cycle injects fuel later in the power cycle. First, Not all the bio is burnt and will cause dilution of the crank case oil. I run oil tests randomlly on all my diesels and after running 25% bio the alalysis came back way over. I do not have the research link infront of me but if you want i will find it. This breaks down the engine oil. Second, high ratios of bio can cause to the particulate filter to become clogged.

As for my mileage on the LLM, @18k I am averaging 17.2 combined. I am running 25% GTL with ULSD.

craigth

05-16-2008, 12:59

:( My average mileage is still 10-11 with 6K miles on my '08 2500HD Crew 4WD. A buddy of mine has an '08 3500 same model with 20K and other LMM work trucks. ALL get the same low MPG! Not sure how you guys are getting the mileage you claim!! How are you calculating your MPG?!

I'm very UNHAPPY with the mileage and am considering selling/trading for a Dodge Cummins. There is no way an '08 that is six years newer than my '02 should get 5 MPG less!

Sivrug2

05-17-2008, 05:14

Craigth,
Calculating MPG is pretty simple. Never trust the on board info.

With your LMM your mods are hurting your mileage. The 6" lift and 305's are doing a 4-5 MPG hit. My experience with lift and big tires has always shown this. On my 2004.5 Duramax the pickup went from 19-21 MPG highway to 12-14 when I lifted and 305's.
I think the best mod for mileage is a Scanguage and using the "right foot mod".
The only time my mileage on the LMM is sub 10 is when pulling a 24 ft goosneck with a 18K backhoe on it. If I drive like a bat outta hell I can even get 4-5 MPH.

More Power

05-17-2008, 12:53

Those who shift their wants & needs more toward fuel economy should consider modifying their trucks along these lines:

http://www.thedieselpage.com/features/11SEMAc.jpg

Lowering the truck and adding aerodynamic improvements will help with fuel economy. ;)

Jim

02bymorris

05-19-2008, 10:09

my 08 Silverado LTZ crew-short box LMM averaged 17.5 local driving. I swapped the ECM to a Kennedy custom and piced up 2 more mpg. have not tested it yet on a trip. all stock except for the ECM

Runaway_Dmax

05-19-2008, 10:31

my 08 Silverado LTZ crew-short box LMM averaged 17.5 local driving. I swapped the ECM to a Kennedy custom and piced up 2 more mpg. have not tested it yet on a trip. all stock except for the ECM

Even the exhaust system is still stock?

50+

05-20-2008, 05:56

Towing I get 10-11 and thats towing heavy, gross wt of 19k +. Local driving I get 14 -15 and the dic is usually around 15.4. On a highway run with few starts and stops and keeping the speed at 55 - 60 it will do 19+. On the same run at 65 it knocks mileage down to 17. All hand calculated. I can usually tell a regen if I watch the dic because it will go down about 2 mpg from where it normally will be. My LLY would do a little better than the LMM, but not much. I like the truck.

RaiderCoach

06-09-2008, 12:46

I now have 20K on my '07 LMM. My truck has 33" tires and a 4" lift, I'm sure that hurts mpg a bunch. I'm also running a Bullydog programmer at the medium (tow / econ) setting. Unloaded freeway driving I'm averaging 19 mpg and in town driving about 13. Loaded with trailer (about 12000 lbs plus truck), it drops down to under 14 on the hwy. I have found that the speedo correction from Bullydog does not work. I called them, but received the 'we haven't heard of that from anyone else so there's nothing were going to do about it' response. But, the speedo is off by about 3 mph, which would affect the mpg upward a bit, but I'm not a good enough mathametition (sp?) to figure it out. So the mileage is improving as the truck gets more miles on it. I would also agree that 55 - 60 is the sweet spot, at 70 I drop by about 2 mpg. Adversely, my '03 duramax improved it's mpg as the speed increased...

Ric

06-23-2008, 16:12

craigth

06-24-2008, 09:05

Thinking of a new Dmax Chevrolet 2500HD 4x4

Reading all of your woes regarding mileage, how many of you who are hand calculating mileage, know that the odometer is reading correctly?

I've always thought that this plays into alot of folks differential in mileage claims...

And if all your odometers are accurate, is it possible that some here have different rear axle ratios causing different mileage as well?

MAN I don't want a ford.... ptt flaaaa yuk.... there I got it out of my mouth! But I did expect these newer diesels to be fairly efficient????

If I were to do it over again, and especially with the $2.99 for 3yr gas purchase promotion, I would check out a Dodge Cummins.

I agree that in my case the speedo and odometer are probably not accurate due to the larger wheels but. hand calculating nets the same piss poor 10-11MPG. Larger tires should NOT make that much difference in MPG vs stock tires! With the Duramax I should be getting at least 13-15 if not higher considering some on this forum claim 17-20, which sorry, I don't believe!

I did find cool product that I would like to try. It's a solenoid operated exhaust bypass. I think the gas mileage issue in these Duramax's is partially related to all the smog crap they put on in the exhaust. Check out http://www.streetpro.us/PowerMasterPics.html

More Power

06-24-2008, 10:59

Larger tires should NOT make that much difference in MPG vs stock tires! With the Duramax I should be getting at least 13-15 if not higher considering some on this forum claim 17-20, which sorry, I don't believe!

What sort of fuel economy did you get with a completely stock truck, stock tires, stock programming, etc., and driving at a constant 65-mph on the Interstate?

Jim

AKMark

06-24-2008, 17:21

Those tires are pretty heavy, that makes a bigger difference than most realize. Also, how far off is your speedo now? Make sure to take that into consideration.

leolkfrm

06-25-2008, 05:49

The lift kit won't affect as much as the tire size, With 373 rears and adding bigger tires the allision computer starts changing things, sensing the load from the tires it adjusts to more of a tow mode, changes the shift points and converter lockup.
I know of a truck with 22.5's that won't go into full over drive lockup untill 25mph because of the matchup of tire to rear end.
As always it takes a diesel a long while to break in compared to gas. It took about 17000 mi to notice a dif in my cat330

Ric

06-25-2008, 12:07

If I were to do it over again, and especially with the $2.99 for 3yr gas purchase promotion, I would check out a Dodge Cummins.

I agree that in my case the speedo and odometer are probably not accurate due to the larger wheels but. hand calculating nets the same piss poor 10-11MPG. Larger tires should NOT make that much difference in MPG vs stock tires! With the Duramax I should be getting at least 13-15 if not higher considering some on this forum claim 17-20, which sorry, I don't believe!

I did find cool product that I would like to try. It's a solenoid operated exhaust bypass. I think the gas mileage issue in these Duramax's is partially related to all the smog crap they put on in the exhaust. Check out http://www.streetpro.us/PowerMasterPics.html

I really don't know. I think if your tires are 10% larger than stock diameter, that affects the circumference greatly (10%) and hand calculating cannot make up for that. Let alone the electronic thinking the ECM and allison are doing for you.

For instance, the DIC on my 6.0 1500HD 4x4 reads "average" 10 to 11mpg if I let it figure over 3-4 tankfuls of normal home and business driving.. My tires are 305/70/16 Wranglers and I guess they are about 10% larger than the toy tires which came stock on the HD.

I cannot speak for the innacuracies of the DIC regarding gallons used because I doubt any of us know for sure we get an exact gallon at EVERY pump or not, so that's another variable.

I do agree that I expect more than 10-12 mpg or I'll just keep my 6.0HD.........

vsp114

07-18-2008, 15:52

2008 2500 HD crew cab, long box bought in March, don't drive it much yet, but with about 5,000 miles, getting between 17.54 to 18.81 hand calculated. Mixed driving.

mesam57

08-22-2008, 19:08

Just took delivery. 1 tank so far. Dash shows 14 - 16 in city. Highway driving can be good or bad; Seems the truck likes to run about 68 - 70 mph and 1800 rpm's. Running here the dash shows 22.6 mpg. Push the speed above 70 and 2100 - 2200 rpms and the mpg drops to 17 - 18 mpg.

I read about the priogrammers and the results don't seem to justify the cost.

I here (rumor) that the 2008's have a tattle tale in the on board computer. Do theses things void the warranty?

Ric

09-02-2008, 16:18

Well I bought the 08 Crew Cab short bed 4x4 chivvy with Duramax

Riding home the DIC calculated 22mpg with 1hr of freeway only driving... round town averaging with that freeway run over the next couple of days, the DIC is calculating 14 to 15mpg... Dunno bout the accuracy til I do some hand calculating to check GPS speed to the truck speedo and then hand calculate MPG...

I need to study this site more to find out about all the programmers etc because I do intend to run 305 70-17's on this truck

By the way, what is with the cooler thingy for the fuel being down near the ground in front of the fuel tank with no protective skid plate?

Sivrug2

09-03-2008, 11:14

There is a tattle tail feature on the LMM's that keeps track of the programming/flashes. This was relayed to me by the shop foreman and friend at the local GMC dealer.
I recently did a turbo back exhaust and installed a "Spare" computer that was programmed mild upgrade/tow.
Hand calculated my mileage in town is up 1-2MPG on the highway 5-7 MPG increase.

Ric

09-05-2008, 08:38

SlimWallet

11-03-2008, 21:42

New 2008 GMC 2500 DC Crew cab....Colorado

First tank....mt, mixed town and highway.....16.2 mpg

Second tank.....mt... up the mountains to go fishing...mostly highway and 70 mph.....17.4 mpg

Hand calc'd

Slim

Duramaster

11-04-2008, 08:34

The ECM is supposed to keep track of the last 10 program reflashes.

mgscustomtune

04-26-2009, 20:16

Here is a few pros and cons in the way mileage is calculated
When you calculate by hand you have no control over the temp factors,wind,grade to a given point which all effect the rolling stance of the truck. l recently did a calculation using a GPS and the on Board readings. I went 25miles constant speed 55mph pulling a 10,000lbs load the GPS and on Board Computer matched up exactly in distance with an average of 12.5mpg on the Computer. The next day which included some tempature change (5degrees higher) and wind(almost at zero) did the same trip. I got 13.5mpg. The on board PCM calculates the mpg including the wind/grade of road you are traviling on and temp change where calculated by hand you do not include those factors. I also took out a 2008 5.3 l was tuning at my shop drafted a transport on the HWY at 55mph l was amazed watching the onboard compter change from 22mpg not drafting to 25mpg when l drafted the the transport l think the onboard computer are a little moe acurate than we think. It is no secret that the New Exhaust Filter System hiders gas miliage and the amount you can strech the Custom Tune without a Delet of the System. Just my two pennys worth

agmakar

05-12-2009, 10:18

christophersond

05-12-2009, 11:07

I own a 2006 Chevy 2500 HD Dduramax w/ 31,000 miles. I'm looking at buying the 2009 GMC 2500 HD. I'm not too comfortable buying the new deisels with all of the emmission mandates from the EPA thus having a reduced Fuel mileage than what I already have. I'm just getting 17 MPG in combined City and HWY driving mostly HWY, (54mi HWY, 13mi City).

What has been the AVG MPG in the new trucks now?
I have a 2009 GMC Sierra, Crew Cab, 4WD, with just over 3100 miles on it. I haven't had an opportunity to check highway mileage yet, but in-town I am getting just over 14 MPG. As with the other Duramax trucks I've owned, I'm confident the MPG will increase as more miles are put on the truck.

craigth

05-13-2009, 09:33

I own a 2006 Chevy 2500 HD Dduramax w/ 31,000 miles. I'm looking at buying the 2009 GMC 2500 HD. I'm not too comfortable buying the new deisels with all of the emmission mandates from the EPA thus having a reduced Fuel mileage than what I already have. I'm just getting 17 MPG in combined City and HWY driving mostly HWY, (54mi HWY, 13mi City).

What has been the AVG MPG in the new trucks now?

Unless you have a very compelling reason to get a 2009 I'd keep your 2006. The new trucks are nice with the exception of the gas mileage. I had a 2002 that got 14-15 City and 15-19 Hwy. My 2008 gets 10-11 City and 14-16 Hwy.

The other thing to consider is that aftermarket chips/computers are not recommended as they will effect the new emissions equipment.

agmakar

05-15-2009, 09:17

There are no compelling reason other than getting a newer model with the added options and having a newer model before I retire. I like to research performance by asking others on thier experiences to get a better guage on what is going on with the new Truck inventories because the Manufactures and dealers will not tell the truth. I know fuel mileage ALWAYS takes a hit when new emmissions equipment are added I just did not know how much of a hit the new engines are taking. For me, fuel economy is first on my list when making truck purchase decisions.

Sometimes I think it's done on purpose to kill the deisel engine for other than commercial use.

denny-o

07-23-2009, 11:39

mpg for city driving will be all over the place.. I can put you on the loop in DC at 4PM and I guarantee 5mpg at 12mph average...
And a similar story for highway mileage depending on how you drive..
To give some perspective I have a 2007 Silverado 1500 4X4 with the small gas V8... I drive like a little old man
(Wait! I am a little old man, ah jeez, and now we've changed Centurys... Damn I hate it when that happens...)..
I get 16.8 mpg average in mostly rural driving with a bit of village tossed in (1 stop light) and once a week to the big city... You Duramax fellas with your 16 mpg average are doing just fine...
Before that I had a 2004 Silverado 4X4 with the 350 V8 and got - TADAAAA - 16.5 mpg average...
I just bought a new, dealer left over, 2008 Duramax 2500HD CC SB 4X4 and will be pleased if I get 16...

denny-o

christophersond

07-31-2009, 12:26

I just returned from a round trip from Cheyenne WY to Ogden UT. I put a total of 997 miles on the truck, and was towing a 5th wheel for a combined weight of 17,970 lbs. I had the transmission in the Tow/Haul mode, and the cruise control set at 75 MPH. Given the fact there are only 7900 miles on the truck, the number of construction zones, and the number of significant grades on I-80 between Cheyenne and Ogden, I am not disappointed with the 8.8 MPG. The ole Duramax just kept on trucking.:D

richp

08-01-2009, 05:08

Hi,

We're in the middle of a trip from Illinois to Pennsylvania and back, towing a 12k fiver.

Hand calculated towing mileage at 55-60 mph (rolling hills, mix of interstate and secondary roads) has been right at 11.4 mpg. Hand calculated mileage tooling around without the trailer (driving between quilt shops and other attractions) for several days was 18.6.

Puzzle -- I have yet to be aware of this truck regenerating -- even when I'm home and driving locally in suburban Chicago for months at a time.

FWIW.

WyoDutch

11-04-2009, 06:27

I just took delivery of my '09 Sierra 1-ton xtended cab on Monday. It's still in the break-in period, but mileage is hovering between 18 and 19 at speeds primarily in the 55 to 70 mph range. Average altitude around 5,000 feet here. Heading up and over the Big Horns today... steep grades up to just over 9,000 feet.. will be interesting to see what the average drops to.

Thanks GM and UAW... You make one helluva truck.

My son is getting 22 mpg with his 2004 3/4-T Duramax, but I doubt I'll be able to wring that kind of result out.

trebin

11-28-2009, 10:30

I have an 08 CC 3500 Dually 4x4 Duramax/Allison and get 14 driving and 10 towing a 24ft gooseneck. Truck has 10 thousand miles on it. Was hoping for more. Had a 03 2500 LB 4x4 with 245's that got 18.5 driving 80-85 mph. Really would like to see more mpg. The Dually has 17's on it but can't go to bigger tires because the duals would rub.

pamax

11-28-2009, 11:40

I have a 2009 Crew Cab HD2500 with 587 miles and I am getting up from 14.6 new, to now reading 15.2 on the computer. My 01 would get a solid 17 on the same trip running at 60 mph. So far can not tell if it went through regen or not but the tail pipe stays clean.

WyoDutch

01-21-2010, 18:56

2009 3500 4X4 Xtended cab SRW. Running 1/2 ounce of Opti-Lube XPD per gallon of fuel.

19MPG, running our 65mph speed limit over all sorts of terrain.

havenopower

01-27-2010, 21:54

My 2004 gets like 10mpg with all the mods but my 2006 lbz gets no better than 12mpg in town stock with no cat of muffler. tried a super chip junk

WyoDutch

02-07-2010, 09:13

At the 6,000 mile mark:

Non-synthetic motor oil
8 ounces of Opti-Lube XPD per 40-gallon tank of fuel
No bed cover or other addons.

Just did a run to Texas and back (3,200 miles). Drove the speed limt... ranging from 55mph to 75mph. The last 400 miles, had 500 pounds of bagged corn in the back.

Overal mileage came in at 18mpg for the trip.

I'm pleased.

EdHale

02-07-2010, 11:23

I drove from Atlanta to Titusville, FL yesterday (475 miles). All interstate and all at 75 mph and my mileage was 36-37. Seriously.

Oops! Wrong vehicle. I was driving a 2007 Chevrolet Cobalt.

ororke1

02-24-2010, 08:28

I got 19.5 mpg on a recent trip with my 09 Siverado. 6000 miles on it, 68 mph empty. Around 15 local driving.

nomad03

03-08-2010, 20:40

richp

03-09-2010, 07:17

Hi,

A couple of weeks ago, I did Chicago to near Grand Junction, CO, with my '09 LMM.

Actual calculated fuel economy on the last two legs of this trip (topper on truck, cruise control on 65, short stop-off tooling around in Denver), was right at 20 mpg. I know from prior trips that running without the topper costs me about 1.5 mpg on this same route.

FWIW.

Chevy Boy

03-13-2010, 07:08

I been using this Excel file for 5 years now with some modifications and it works really good and it's accurate..........been averaging 19.6 mpg on my 2007 Silverado LT 1500 over a 3 years period.

http://www.uklegacy.com/forums/index.php?act=attach&type=post&id=2651

Runaway_Dmax

03-13-2010, 08:06

I will get 17-18 hiway at 75 with no trailer in tow, if I am pulling ANY trailer from a small utility to my 29 foot rv my mileage will drop to 8-11. I am not very inpressed with my towing mileage. Power is great.

I am running 285/75/16 and have had GM reproram the system, also a K&N air filter, and a supper chip programer. I can set the programer on any setting and it will not effect my mileage.

I have 25k miles on the truck.
is this nomal mileage for this truck?

2007.5 LMM

I do not believe your dealer can adjust a DMax truck to your tire size - the ABS system yes they could, but for speedo - no.

If you still have the DPF in place, your programmer is causing the truck to regenerate more often and will result in lower mileage.

Your K/N filter is a big no-no for diesels. Yes it may allow more air into system, but more dirt as well. There have been independent tests done that show the stock air filter does the best at stopping dirt.

My truck is an 08 CC/long box and its hovers between 18 - 19 mpg and towing my 28 ft fw and atv trailer in tandem 10 - 12 mpg. I hit the magic 20 mpg mark once in the 38K I have owned the truck.

BMDMAX

04-02-2010, 15:06

I recently completed a round trip from Atlanta, GA to Loyal, WI to pickup my LB7 race engine from Kennedy Diesel. We burned 105.4 gallons of diesel over 2,137.2 miles for a trip average of 20.27 MPG. The highest leg was 21.0 MPG and the worst segment was 18.8 MPG. All cruise speeds were 73 to 78 with some bursts in the 80's. The 18.8 segment was bumper to bumper rush hour traffic in ATL.

All mileage was hand calculated.

This was with the KD Tow Tune ECM and DPF delete with the KD four-inch exhaust. Everything else is stock on my 2008 LMM. Very happy with the KD tuning on the LMM.

I highly recommend the KD tune for those wanting to bump up their mileage on their LMM. :cool:

crazydave01

12-26-2010, 17:42

08 GMC CCSB. Front leveling kit only, 305/50/20 tires(actual height is 32")

Best tank on highway 14.8
Avg highway 13.9
Avg local 12

Hauled my motorcycle trailer today and got 8.2 MPG. It only weighs 4000 loaded. My 06 silverado with a 5.3 got 10 MPG everytime on the same trip, same trailer.

Diesel fuel 3.399 gal = very expensive and disappointing.

All mileage figured by GPS and amount of fuel pumped at the station. The DIC shows worse mileage than actual.

KD ECM on the way. Hopefully it helps

FYRWOOD GUY

05-08-2011, 10:05

my 2011 3500HD with the break in oil still in motor at 2560 miles is telling me via the dic that fuel mileage is 14.8 and seems to be climbing during this break-in time. i am going to run mobile devac elite synthetic diesel motor oil. i guess i should start keeping track of mileage the old fashioned way after i dump the break-in oil.

http://i116.photobucket.com/albums/o8/WILLIAMFGREENE/th_DURAMAX5.jpg (http://i116.photobucket.com/albums/o8/WILLIAMFGREENE/DURAMAX5.jpg)
http://i116.photobucket.com/albums/o8/WILLIAMFGREENE/th_DURAMAX6.jpg (http://i116.photobucket.com/albums/o8/WILLIAMFGREENE/DURAMAX6.jpg)
http://i116.photobucket.com/albums/o8/WILLIAMFGREENE/th_DURAMAX7.jpg (http://i116.photobucket.com/albums/o8/WILLIAMFGREENE/DURAMAX7.jpg)

would like to read about other 2011's

Mark Rinker

05-08-2011, 18:54

Great looking rig...nice chainsaw/logging website!

www.MREBoatTransport.com (http://www.MREBoatTransport.com)

JohnC

05-08-2011, 18:55

Diesel fuel 3.399 gal = very expensive

Ah, for the good old days! ;)

prairiewind

01-20-2013, 07:50

I have owned a 2002, 2004 and now 2008 3500 HD. Got 17 to 19 in first two. I have 72,000. on the 2008, got 17 when first purchased, now 12 to 14. When I take to dealer and they reflash I can get 19, this will las for a few tanks of fuel then back to 12 to 14. I can put my auto zone tester on and there will be no codes, I reset codes, even though there are no codes, and I go back to 18. I would like to put an edge cts and an exhaust brake on but would like to figure out what is wrong before I do anything. Dealer has no idea.

DieselDavy

01-20-2013, 19:58

Are you hand calculating?

prairiewind

01-21-2013, 06:58

Yes, mostly, I pretty much use this truck for trips, I can look at the fuel guage and the milage and tell what is going on. Last summer I had the fuel system cleaned and they reflashed at the same time. I made several trips pulling a 4 horse slant and got 13, a couple of months later I made the same trip empty and got the same, 13. I went back to the dealer and another reflash and back to 17 to 19 depending on how I drove. These trips are over I70 from Denver to Page AZ. I also have a 30' Montana and when everything is running right I can get 10 to 12 when in my lame mode I get 6 to 9. When I started resetting my codes, even though they don't show up it doesn't make a difference right away but after a couple of hundred miles I can actually feel the truck respond. The truck goes from sluggish to very responsive, you know exactly when it happens