2004.5+ LLY Duramax Fuel Economy Poll

[REDTRUCK05]

I own a 2005 2500 HD LT crew cab. MPG has been ugly since delivery. I average between 14 and 15 empty and if I am pulling my 5600# travel trailer, I get between 9 and 11

[rob from bc canada]

These poll results are definitely weird.

Has anyone ever pinned down a cause for those who experience such low mileage?

The numbers of them according to the is poll seems high enough to warrant a dedicated search for the problem.

Any mileage poll should show a bulge in the mid range, and not at both ends.

I drive for best mileage, and with the heavy 3500 4x4, I can reliably get a measured average of near 13 l/100 km (17.5-18 US mpg) driving 80% highway averaging 100kmh = 60 mph, 20% local, with a steep hill for 1.5 km up to my house at the end of each trip. That really cuts it down - it does burn 1-2 l coming upo that alone.

If I reset the computer on the highyway after it's warm, I can get down to 12l/100 = 19.6 mpg average over a 100 mile drive which is probably a bit optimistic. My DIC tends to be at least 1 mpg higher (.5 to 1 l/100k low)

With a high 3000 lb camper on, doing 100 on the highway consumption goes up to 18l/100 = 13 US mpg

These figures are not fantastic, but given the weight of the truck when compared to my old K2500 93 6.5 TD Standard shift which weighed about 1500 lbs less, seem more or less reasonable.

All this leads me to believe that either the poll results are off somehow, or a large number of the 05 LLY's have a significant problem, which could be fixed, because they can do better.

[More Power]

The following two forum threads might help, both to explain fuel economy differences people see and to help troubleshoot a low MPG truck.

http://www.thedieselpageforums.com/t...ad.php?t=22302
http://www.thedieselpageforums.com/t...ead.php?t=9675

Jim

[USA-1]

16-17 MPG mixed 20 MPG highway at 1800 RPMS.
USA-1

[rob from bc canada]

16-17 MPG mixed 20 MPG highway at 1800 RPMS.
USA-1

Would that be per the DIC, or calculated from tank fills, and recorded miles?

I find the computer is 1-2 mpg optimistic.

In any case, for a 3500DRW that sounds pretty good, or absolutely excellent if it's calculated.

By the way, are there any steep hills in your area?? It seems hauling the 7000 or so lbs up hills seems to bring it down quite a bit.

[Finman]

Got 17.4 on a 1900 freeway trip-no load. Get under 10 pulling 8000lb 5th wheeler. 14-15 around town driving.

[REDTRUCK05]

I have a brand new 2005 2500HD with almost every option and I am getting 15.8 around town and 21.9 on the hwy. What are people using to increase fuel economy?

I could only wish to get that!

[EZHAULER]

I consistently get 15-16 mpg around town driving. (Easy with the foot-driving). I do not do much long Highway driving without a load- but with my toyhauler loaded 12K+ I consistently get 8-9 mpg @ 70-75 mph. I got as high as 11 mpg once trying too increase by driving 55-65mph. ALL hand calculated- filling up till I could see it in the neck. I'm going on a 1600 + mile trip next week, First trip after installing upgrades-EDGE Juice W/Attitude monitor & Cat back exhaust. After getting alot of info off the forum EGT/MPG. I'm going to try and use control and see how good it can get. Follow up info in a cpuple weeks.
__________________________________________________
2004, LLY 2500HD,CC/SB 4X4,Edge Juice W/Attitude Monitor
MBRP 4"Cat Back Exhaust,K & N Air Filter,60 Gal Aux Fuel Tank
Sprayed in Bed Liner,Firestone Air Bags,Front End leved W 305/50 R20 Tires

[REDTRUCK05]

16-17 MPG mixed 20 MPG highway at 1800 RPMS.
USA-1

What is that, about 55 mpg?

[DaveMcClain]

I have a Gulf Stream Ultra with the Kodiak chassis, Duramax LLY,and Banks Six Gun, and at 55MPH, I achieve 15.2 MPG! When pushing to 65 MPH, level territory, the mileage drops to about 12.5. Must be wind resistance.

[Kelly T]

Updated - over 25,000 miles now. 19 MPG seems to be working. Bone stock. 2500 HD CC.

http://home.columbus.rr.com/vfrket/Diesel/Diesel.xls

Note my calculated Miles Per Hour (miles for the tank divided by elapsed time (hours) from the from the DIC) to the far right. BTW, I still like my spreadsheet. There are few rows of data where I had to add a couple tanks together.

Kelly

[fourtenposi]

Has anyone ever looked at the corralation between between getting poor fuel economy and what kind of topper/bed cover they have? I pulled off my high rise topper and I have seemed to gain 3-4 MPG. I only have put about 40 miles on the truck since, but the change seems dramatic. Has anyone seen any results like this? I have made no other changes to the truck. I have a 2005 GMC 2500HD EC 4x4.

[rob from bc canada]

I very much doubt the topper has much to do with it. At most I think you would be getting 1/2 mpg variation for wind resistance.

Mileage can vary dramatically depending on many factors such as wind direction relative to travel (if your going 70 against a 50 mph wind, its just like doing 140, and going the other way would be like doing 20)

In such a short distance, relying on the computer, I find mine reads higher near the top of the tank, and lower mid tank.

Load, speed compared to your average, hills, stops and starts, etc all can affect your reading.

18-19 mpg unloaded 60-65 mph with a few starts and stops thrown in seems to be fairly normal.

[troyf63]

I get between 19 and 21 MPG on the highway at 65 MPH. When I get on it though, it declines significantly. I really like the power when I can keep it out of the shop.

[XTeam524]

Mine does good between 55-64 I can get around 18-20 depending on the day, but if I go any thing over 65 it goes down to 16 even 15. I think that is a bunch of crap. Why can a semi pulling 60,000lbs get 6-7 and my pick-up cant get 10 pulling a 40 enclosed trailer that only wheighs 7000lbs.

[almo]

I just bought a 04 3500 D/A 4x4 lly with 53400 miles. Switched to synthetic motor oil & trans oil. AT a nice easy 65 cruse I get 19 to 20 done by hand. To soon for other milage.

[Freightliner3]

The best and most repeatable mileage is 19.4 empty.I live in the farm country of Minnesota,so most of my miles are hiway.Where the 2005 LLY shines is when I tow my skid steer and attachments,about 11000 lbs.In 24000 miles it has kicked out of Over Drive 2 times. I have added the BD manifold update.I have on order the Banks monster exhaust system and the Banks Air Intake.Will see if they make any difference.My main interest is pulling small heavy loads.If I need to pull large loads I use the Freightliner.

[BigRabbitMan]

I have a Gulf Stream Ultra with the Kodiak chassis, Duramax LLY,and Banks Six Gun, and at 55MPH, I achieve 15.2 MPG! When pushing to 65 MPH, level territory, the mileage drops to about 12.5. Must be wind resistance.

What does your rig weigh? I am considering putting a D/A into my 15,000# FMC in place of the original 440-I.

[kantra]

I have only 750 miles on miy 6.6 and it gets 15.2 per gallon and 11.4 towing my fifth wheel camper 13000lbs I figure that is not bad for an engine not even broken it yet

[kantra]

With 1000 miles on my truck I pulled my 14000lb fifth wheel home the other day not knowing the truck was in 4 high when I checked my milage it was 14.4. But in 2 wheel drive its only 11.3 what gives with this??