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Thread: LMM Fuel Economy

  1. #41

    Default Update and test...

    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.

  2. #42

    Default Fuel mileage

    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

  3. #43
    Join Date
    Nov 2001
    Location
    Windsor, CO USA
    Posts
    75

    Default

    Quote Originally Posted by kratos1 View Post
    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...
    Silverado 2500HD CrewCab 8.1/Allison; Auto; SB 4x4; Indigo w/ red striping; Z85 Graphics; BF Goodrich 285/75R16, StylEyes headlight covers; 4-lamp conversion; 3M Bug shield (clear adhesive film); tinted windows; taillight guards; Rhino-lined; Extang Sabre Tonneau; Escort 7500; Uniden 538W, Flowmaster#530504 dual exhaust, K&N Fuel Inj. Performance Kit, Black Westin Bull Bar, PIAA Air Dam with PIAA 40-series, Roadmaster ActiveSuspension (like a kicker shock)SRB lights, Rancho RS9000\'s in each corner<p>POLARIS Xplorer 400 4x4 - FUN!!!

  4. #44

    Default Mpg

    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!
    2007 3500HD Crew Cab, LB LT2 SRW

  5. #45
    Join Date
    Oct 2007
    Location
    Wet Coast of Canada
    Posts
    19

    Default Fuel mileage

    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

  6. #46
    Join Date
    Jan 2005
    Location
    St. Louis, Missouri (pronounced misery)
    Posts
    203

    Default losing fuel mileage

    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.
    Scott
    St. Louis, MO


    '06 Silverado K2500 4x4 Crew Cab D/A "Big Max" AmpResearch retractable Running Boards, 4" Turbo back Kennedy Exhaust, Kennedy Custom Tune!
    '99 BMW K1200LT "Special K" my other "SUV"
    '07 Salem by Forest River Fifth Wheel Toy Hauler

  7. #47
    Join Date
    Oct 2007
    Location
    Wet Coast of Canada
    Posts
    19

    Default Mpg

    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

  8. #48

    Default followup on Bio Fuel economy

    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!

  9. #49

    Default LMM Fuel Economy

    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).


    2007 Silverado Duramax LMM ... Engine Bone stock so far. Line-X bedliner. B&W Turnoverball.

  10. #50
    Join Date
    Aug 2007
    Location
    S. Texas
    Posts
    4

    Default Bio in LLM

    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.

  11. #51

    Unhappy Consistent average MPG is still 10-11 with 6K miles!

    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!

    2008 GMC SLT 2500HD Crew Cab SWB 4WD ZLT
    Black / Titanium
    Sliding Rear Window
    Integrated Trailer Brake
    Billet Grill
    Pro Comp 6" Lift Kit
    Helo 17" Wheels
    Nitto Terra Grappler 305/70/17 Tires
    Spray-In Bedliner
    Weather Guard Low Profile Aluminum Saddle Box
    Remova-A-Ball Gooseneck Receiver

  12. #52
    Join Date
    Aug 2007
    Location
    S. Texas
    Posts
    4

    Default

    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.

  13. #53
    Join Date
    Feb 2000
    Location
    Montana
    Posts
    11,380

    Arrow

    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

  14. #54
    Join Date
    Feb 2004
    Location
    Augusta, GA
    Posts
    10

    Default Lmm Fuel Economy

    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

  15. #55
    Join Date
    Jan 2007
    Location
    Somewhere between WI & WY
    Posts
    149

    Default

    Quote Originally Posted by 02bymorris View Post
    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?
    08 Blue Granite Silverado LTZ, DMax/Ally, CC/LB/4x4, Cab lights, Camper mirrors, Brake controller, Sunroof, Park assist, and skinny tires

    06 Jetta TDI

    00 Jayco 263RK (2nd home)

    upgraded to an "09" Ranger 619VS/full windsheilds, w/an ETEC 225HO, T8 kicker, Minnkota 101 Terrova, and Lowrance electronics.

    Real Trucks have LONG BEDS!

  16. #56
    Join Date
    Jun 2005
    Location
    Iowa
    Posts
    50

    Default

    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.
    08 2500HD LMM D/A Ext cab sb LT1 4x4 Greystone Metallic. 265 75r 16 Mastercraft Courser C/T 10 ply's. B&W GN. Pull 20' STL Featherlite Combo trlr.

  17. #57

    Default Another mileage update...

    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...

  18. #58
    Join Date
    Jun 2008
    Posts
    15

    Default New Here

    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????

  19. #59

    Default

    Quote Originally Posted by Ric View Post
    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

    2008 GMC SLT 2500HD Crew Cab SWB 4WD ZLT
    Black / Titanium
    Sliding Rear Window
    Integrated Trailer Brake
    Billet Grill
    Pro Comp 6" Lift Kit
    Helo 17" Wheels
    Nitto Terra Grappler 305/70/17 Tires
    Spray-In Bedliner
    Weather Guard Low Profile Aluminum Saddle Box
    Remova-A-Ball Gooseneck Receiver

  20. #60
    Join Date
    Feb 2000
    Location
    Montana
    Posts
    11,380

    Default

    Quote Originally Posted by craigth View Post
    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

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