2004.5+ LLY Duramax Fuel Economy Poll

[B. Lane]

05 REG CAB WT PACKAGE. 2300 MILES ON TRUCK. CRUISE SET ON 70MPG, MANUALLY CHECKED LAST WEEKEND AND GOT 18.3MPG. ALL HIGHWAY. I GET 14-16 AROUND TOWN. PULLED 4K-5K TRAVEL TRAILER IN SUMMER AND GOT 14-16MPG WITH CRUISE SET@65. MILEAGE SEEMS TO BE GETTING BETTER.

[AndyU]

Originally posted by AndyU:
Well, after thorough testing, towing, empty, highway, city, etc, my mileage went down with the Predator. Running empty, I lost about 1.5 mpg in city driving and about the same loss highway. Towing was about the same, maybe even a bit better, but it's hard to tell because of the affects of wind direction, rate of travel, etc which makes it hard to get a good baseline. The Predator caused my DIC to indicate my mileage went way up, but hand calculating my fuel usage revealed that in fact it went down. Very disappointing.

After restoring the factory program I averaged 19.5 mpg on a 550 mile trip last weekend (empty at 70 mph w/ cruise and a tail wind). I got 22 mpg on the last 100 miles (empty, no wind, 60-65 mpg w/out cruise) after refueling. I think that's pretty good.

The truck definitely gets better mpg w/out cruise on, letting the truck slow up a bit ascending hills and speed up a bit going down. Also, if I keep it at 65 or less my mpg is much better. Also no hard acceleration.

I only have 5000 miles. I'm very happy with this truck.

Quick update. I now have 15,000 trouble free miles on the truck. I added an Edge EZ and I run with synthetic oil. I can now get as high as 24 mpg if I can roll along at 55-60 without any stopping. The norm is more like 22 hwy and 18.5 city, subtract 1 mpg when running with winter blend fuel. The Edge EZ definately gave me at least 1 mpg better, maybe a bit more.

[Dannyboy]

I have 2500 miles on the 06 and my highest mileage so far is 19.5. I'm really impressed so far. My avg. since new is 17, but keeps getting better. My father has an 05 lly and the best we ever got with that is 17.8.

I'm really happy with this truck!!!

[REDTRUCK05]

Originally posted by Cliffee:
I'm averaging 16.5 with mostly short city trips. 1800mi on OD. 2005 LLY

how fast?

[REDTRUCK05]

Originally posted by AndyU:
</font><blockquote>quote:</font><hr />Originally posted by AndyU:
Well, after thorough testing, towing, empty, highway, city, etc, my mileage went down with the Predator. Running empty, I lost about 1.5 mpg in city driving and about the same loss highway. Towing was about the same, maybe even a bit better, but it's hard to tell because of the affects of wind direction, rate of travel, etc which makes it hard to get a good baseline. The Predator caused my DIC to indicate my mileage went way up, but hand calculating my fuel usage revealed that in fact it went down. Very disappointing.

After restoring the factory program I averaged 19.5 mpg on a 550 mile trip last weekend (empty at 70 mph w/ cruise and a tail wind). I got 22 mpg on the last 100 miles (empty, no wind, 60-65 mpg w/out cruise) after refueling. I think that's pretty good.

The truck definitely gets better mpg w/out cruise on, letting the truck slow up a bit ascending hills and speed up a bit going down. Also, if I keep it at 65 or less my mpg is much better. Also no hard acceleration.

I only have 5000 miles. I'm very happy with this truck.

Quick update. I now have 15,000 trouble free miles on the truck. I added an Edge EZ and I run with synthetic oil. I can now get as high as 24 mpg if I can roll along at 55-60 without any stopping. The norm is more like 22 hwy and 18.5 city, subtract 1 mpg when running with winter blend fuel. The Edge EZ definately gave me at least 1 mpg better, maybe a bit more. </font>[/QUOTE]What level are u running? I average 15mpg at 70-75. Pulling me 5600# travel trailer at same speeds I get as low as 7.9 as hi as 11, pretty ****ty for such a light load. 6500 miles on

[AndyU]

Quick update. I now have 15,000 trouble free miles on the truck. I added an Edge EZ and I run with synthetic oil. I can now get as high as 24 mpg if I can roll along at 55-60 without any stopping. The norm is more like 22 hwy and 18.5 city, subtract 1 mpg when running with winter blend fuel. The Edge EZ definately gave me at least 1 mpg better, maybe a bit more.

I now have 22K miles on the truck without any trouble. That 23 - 24 mpg at 55 with no wind and no stops, etc has held true, but remember, that's a pretty unrealistic scenario in normal life. I just said it to show an absolute best case scenario. Real world was more like 20 Hwy and 17 city this winter under the best conditions and 2-3 mpg lower when in 4x4 with snow and very cold. Still, I think that's very good.

Somethings I've done so far that helped improve my economy. (1) Got rid of my lead foot. Seriously, just keeping a real light foot and slower speeds added as much as 2 mpg. Watching the DIC helped me learn to change my habits. That said, the following mods got me another 1+ mpg. (2) Edge EZ running on level one. (3) Boost Stick, but only when combined with the blocking plate and finger stick to bypass the EGR system. Boost stick with a functional EGR had fuel economy go down. the boost stick has helped towing, but doesn't seem to effect my economy empty.

The mods definately helped my economy towing, adding as much as 2 mpg depending upon conditions. I can get 14-15 pulling my 34' x 8' x 9' goosneck horse trailer (10,000-12,000lb) just going 50 mph on nice back roads w/out starts and stops. Pushing that up to 65-70 drops it down to about 11mpg and pusing up to 75-80 takes it down to about 9. As a rule of thumb, economy seems to drop about 1 mpg for ever 5 mph over 55.

I will be adding a corsa perfomance exhaust w/ down pipe soon. I'll let you know if that makes any difference after I've had a chance to observe it in action for a while.

[tboy76]

Originally posted by eagle in flight:
My LLY has been getting about 18 mpg all by itself. When I tow a fifth wheel (weight around 14,000 pounds) and travel at 60 mph, I get around 11.5 mpg. Mileage is at 15,000.

[omercer]

I am very disappointed in the mileage. I'm seriously considering trading my 05 Duramax in for the new Ford when they come out next year. I have 22k miles and mostly at 75mph on the hiway. The dash readout says 13.9 ave mpg. That's pretty close. The best single trip was 15.9 mpg. Most of my driving is at ~ 5000ft elevation in Northern Nevada. I got the 15.9mpg in California close to sea level. Do you think that indicates something? Please explain to me why there is such a wide range of mpg. It doesn't make sense to me that there can be an 8mpg range for the same vehicle even taking into account different driving styles.

[JohnC]

Originally posted by omercer:
Please explain to me why there is such a wide range of mpg. It doesn't make sense to me that there can be an 8mpg range for the same vehicle even taking into account different driving styles.

Well, I can't answer your question, but I will say that my local driving is pretty rough on mileage. I have a lot of short trips with a lot of up and down hills. I was getting about 13.5 mpg in this cycle with my '95 and I'm getting about 13.5 mpg with my new D-max. The D-max has only about 1000 miles on it and there is the fun factor coupled with the fact that it is a heavier truck, so I'm not complaining.

Also, my DIC appears to be right on the money. Last fill was 18.3 gallons and the DIC showed 18.1 used. Well within an acceptable margin of error...

[mad]

2500 mile report around town driving without towing:
1) Stock I got 16 mpg...
2) Added LDL from FreedomFuel to the fuel and got 17 mpg...
3) Added Magnaflow 4" turbo-back exhaust and now getting 19 mpg...
Later this week I add an AFE Stage2 intake and am expecting to hit 20!

[JD Diesel]

Just took a trip to Los wages. There and back got 17.6 Speed most of the time was 76 mph. We is happy. the old 454 sub best was 12mph. JD [img]tongue.gif[/img]

[Finman]

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

[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.

[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.

[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.

[asm]

I voted less less then 15MPG.

My Duramax is a 2004 Dually with crew cab. When towing a 11000# fifth wheel, going up 395 to Bishop in speed between 35MPH to 55MPH, I get 9.8MPG. 35MPH is not by choice, as LLY is known to overheat when push hard going up a long grade.

I got my best MPG yesterday going from Bakersfield to Orange county to drop off a trailer. The trailer weight about 7000# and I kept the speed between 55 ~ 65MPH. Of course, the returen trip was driven with nothing in the back of the truck. I actually got 14.1MPG. Not as high as some of the 20MPG claim I see here, but much better than 10MPG I used to seeing.