LMM Fuel Economy

[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!

[RaiderCoach]

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]

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]

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]

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]

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

[Sivrug2]

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]

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]

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]

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



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

Jim

[02bymorris]

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

[RaiderCoach]

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]

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????

[craigth]

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]

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

[Ric]

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.........

[Canuck76]

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).