LMM Fuel Economy

[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

[Runaway_Dmax]

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+]

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]

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

[AKMark]

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]

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]

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]

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]

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?