2004.5+ LLY Duramax Fuel Economy Poll

[bthompson]

I have had a 2004.5 LLY 2500HD Duramax for a little over a year. I have a little bigger tires than stock and have heard wonderful stories about gas mileage. As a matter of fact, I have three different buddies with Duramax's 03' or later that have the LB7 engine and average 16-17 around town and have gotten 20 on the highway. I looked at my buddies lifetime average the other day and his was 16.5!!! His is about a year old, but he has the LB7. The guy at the dealership told me the LLY should actually get better than the LB7. What is the deal? My lifetime average reads 12.4 mpg and I have never gotten better than 15 mpg on the highway. I also have an Edge/Attitude performance chip.
I have also read all of these posts about 16-17 mpg and even 20 mpg or better. Most of my miles are unloaded with bed covered, and I do not have a lead foot. Could there be that much difference in engines? Any advice, help, or answers?

[cruzar]

I have just put the second tank of fuel in my 05,
2500 HD long bed and the fuel mileage was slightly
lower than the first tank. On the same road that averaged around 18.9 I now am averaging 17.3. I kept the computer on, just like the first trip, and kept it at 2000 rpm/65 miles per hour. I do consider this a difference. I hope the fuel mileage does not keep going down instead of up. The first tank was filled by the dealer and I wonder if they put an additive to help the octane level of the fuel I also was told that there are to octane levels, 40/44 does anyone know if this is correct.

[Kelly T]

Had 02 1500HD 6.0 gas Crew Cab 4x4 shortbed. Bought 05 2500HD Duramax Crew Cab 4x4 shortbed. Kept fairly tight records on the 6.0 and have modified my spreadsheet to include the new gee-whiz factor of the 05 (automatically calculating data on the fly). Make sure you scroll down to where averages/min/max is calculated too.
First post, first diesel - all stock performance-wise, short bed with no cover - yet.

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

My driving is mixed between around town & highway commute to Columbus (OH).

Average on the gas 02 was 14.14 MPG after 60K miles - again no bed cover. Average on the 05 Diesel is 18.73 - less that 3000 miles presently. The gee-whiz factor of auto-calulating mileage does keep me from pressing the accelerator as hard on the diesel as I did on the 6.0 gas.

Having fun so far. Looking to improve shift points - revs too much at 25, 35, and 45 mph, would like it to shift sooner - will likely go the route of Juice w/Attitude to improve mileage and shifting (to my liking). A little more power now and then never hurt. Typically hauling/trailering is minimal and usually just a motorcycle or ATV. E.G. I raced at Mid-Ohio this past week and hauled my racebike, spares, & associated gear.

Kelly

[Black95TD]

Mine is new - only 800 mi. now. I filled up on way home from dealer and then refilled before a 400 mi trip. 1st 1/4 tank (same station, same spot and tried to fill to the neck) 17.4 mpg rural driving. 30 - 50 mph, some stops, up and down the hills.

Next time, again refilled at exact same spot. 385 miles from Connecticut to upstate NY and back. 2/3 highway at 60 - 65 mph and 1/3 local roads around the lake. 21.1 mpg. I was taking it pretty easy so this may be the best I ever get.

Next tank is looking good too - at this point over 200 miles at 3/4 tank. I haven't reset the fuel indicator but it seems like its pretty darn close.

All in all, exceptional fuel mileage! I considered a gasser but everyone I talked to said they got 10.5 - 12 mpg. The trick will be to take it easy. I'll bet those injectors really pour the oil to it when you jump on it.

[Steve Rapp]

I just drove my 04.5 D/A from San Diego to Spfld Mass. and back and got almost 16 mpg pulling a loaded car trailer. I did a 500 mile round trip trailer less while in Mass. to Pa. and got 20 mpg and the AC was always on. I did 65 mph most of the time.

[fourtenposi]

I have a 2005 2500hd d/a with a high bed cap and all I can say is WOW. The power combined with the fuel ecomony makes this an awesome truck. I asked my buddy how the truck pulled my 26 ft enclosed trailer with the car and he replied "what trailer". Man he was not exagerating. Tons of power. I found at 60 mph on a level grade my truck dic says 23 mpg.It droppes to about 19 at 75. These trucks have alot smaller power band that a gas vehicle so fuel economy will suffer the faster you go. If you want the best fuel economy you need to keep the rpms at peak torque with I believe is 1800 rpms. The engine is most efficent there, that is why it has the most torque there.

[cruzar]

I have noticed a difference in the fuel since I filled up the last tank. This time I filled up at a station that touted premium diesel and my mileage per gallon increased again. This time running at just over 65 to 70 mph I am getting 18.3. This with having to run some hills but not pulling a trailer.I do feel that the quality of fuel and the type of driving has alot to do with the economy. I have enjoyed the vehicle so far, it has been a while since I have had a new vehicle. I now have just a little over 1500 miles on the odometer, the miles are cranking up a little to fast for me, don't want to use it up all at one time.The fuel here is around 2.35 to 2.37 per gallon, I am in Fort Worth Tx.

[daleslad]

This is my first deisel and first post. I don't know anything about deisels so I've read all of these posts with interest.
I bought mine because I wanted better gas mileage and to pull a 5th wheel. I bugged a lot of campers who towed with the duramax about how they liked theirs. One camper even let me drive his around the campground. I was impressed with how quiet and smooth it was .
However I'm not a happy camper, My 2005 has 2500 miles on it and I'm not getting very good mileage out of it.
My first problem was smoke coming out of the exhaust in clouds while driving solo on the freeway and also a rattling noise from under the hood.
The dealer flushed it out and tweaked the software and since then the engine has sounded much louder.
My latest problem has been a tendency to stall when going up a slight incline solo while trying to keep the speed at around 5 mpg. It won't actually stall but will recover and jerk forward which keeps me busy feathering the accellerator pedal.
The same problem manifests itself when I'm trying to back my 5th wheel up my driveway. It can get pretty scary as I don't have much room and it's like threading a needle and I don't like it jerking ahead like it does.
The dealer's answer is to tell me to put the 4 wheel drive into the Low, Low gear when backing up with the trailer.
I had a 2001 Sierra HD 2500 vortec 8100 before this truck and I never had any problems backing up my driveway. My trailer only weighs about 8,000 lbs. max.
Also when I'm pulling the trailer hard up a hill the engine sounds like a threshing machine. If it was a gas engine I'd say the tappets were rattling but I'm not sure just what a deisel is supposed to sound like.
If anyone has any advice or suggestions I'd surely like to hear them.
Thanks everyone it's nice to be able to share experiences with fellow deisel truckers.

[dieselfish]

I'm getting 14.2 avg which is about 1/2 surface streets and 1/2 hwy for my 12 mile work commute.
I now have 3K on a 2005 LLY. The only "real" hwy driving I have been pulling a 9000# 28' 5th wheel and getting about 10.5mpg between Phoenix and Payson AZ. About five 6% grades on the road at over 100deg ambient temp. Tried not to answer the highway because of not running unloaded but it did not like that. I choose 15-16 hwy only because I have yet to see anything over that.

[Kelly T]

Spreadsheet has been updated. Still in the high 18s for MPG.

No new toys on it - still stock. Have just (today) change oil & filter for second time and the transmission filter.

I continue to be impressed with the quality of the post in this forum. I went ahead and joined the members area. I am learning a lot about diesels. Thank you!

[ 08-28-2005, 03:21 PM: Message edited by: Kelly T ]

[cruzar]

You stated that this is the second oil, filter change. Did you change it yourself? if so what filters did you use, I think that someone stated that the oem filters were having problems if so please inform if not direct me to what filters you are using.

[More Power]

daleslad,

Your engine/fuel system has a problem. A competent and motivated dealer service department is what you need most.

I would suggest you begin a new topic thread with your comments about engine running issues. It'll get more eyes....

Jim

[Bugs]

2005 GMC Sierra Duramax/Allison. I do almost all city driving and I average about 14.5.

[Kelly T]

Originally posted by cruzar:
You stated that this is the second oil, filter change. Did you change it yourself? if so what filters did you use, I think that someone stated that the oem filters were having problems if so please inform if not direct me to what filters you are using.

Yes changed it myself both times. Using factory recommended AC filter. Have not seen any posts about issues with it. Only posts I have seen related to the odler style FUEL filter. My D/A CC is 2005.

[cruzar]

Thanks, on the looking into the AC oil filter, how about the fuel filter? I have about 3000 miles on the vehicle now and I am monitoring the computer on the oil filter/ fuel filter change.Just looking for some feed back on the filters being used by some on this board.

[rob@rone.ca]

Has anyone computed the averages for the different models and options ie 2500 or 3500, SRW or DRW, allison or manual, etc???

I'd be real interested to know other peoples comparison with the 6.5 TD's

I had a heavy-duty K2500 6.5 TD single cab standard, and used to get 19-20 mpg empty (converted to us gallons)

With the LLY as below I'm getting 16.5-17 empty in similar driving after 4000 miles on it now.

[mjammer]

I just got back from a 300 mile round trip that was interstate and some 2 lane highway and got a new best of 21 MPG (calculated). Previous best was ~18.5 MPG. Around town and mixed driving (including some boat towing) I am averaging about 15.5 MPG. I am at almost 10K miles now. Mileage is slowly climbing over time as it continues to break in.

[LJ]

Guys, you have to hear this.

I knew when it got broken in better it would get better fuel economy, but this past Sunday I really was amazed.

My mother lives in West Union, WV. I had been visiting her, and was coming home. Two miles from her home, I reset my DIC and thought I'd take my time coming home. It's mostly all 4-lane, but thought I'd put it on cruise @ 55 and see what happened.

There are several big hills. As I topped the hill behind West Union, it was at 16. However, the farther I came the better it got. By Harrisville it had topped 20, and believe it or not under the I-77 underpass in Parkersburg (55 mi) it was setting 24.2!! I went on south on 77 to Ravenswood, and it was at 24.3!!! However, I sat in a Dairy Queen drive-thru for 10 minutes and it fell 2 mpg. I then drove on to Pt Pleasant and after 120 miles total (the last 30 on two-lane) and 10 minutes idling not moving, it was still back up to 23.6!!!

I could not believe that holding it down to 55 made that much difference. I have to tell you that I got some mean glances on the interstate, but to get 6 mpg better that at 70, I can put up with it.

LJ

[r gomez]

my last duramax was an 01 extended cab short box 2wd and averaged 17-18gph in 14 mile round trip to work with 16 stop lights 19-20gph highway when pulling 11000 lb trailor got 13-14gph all hand figured the duromax i have now is a 04 extended cab short box 4wd same driving as the 01 i get 13-14.5gph city 16-17 highway and 11 pulling the trailor city or highway (i can find all kinds af stuff to beef up the truck and ger worse mileage does anyone know what i can do to improve mileage

[rob@rone.ca]

Note to LJ

I had that happen to me once - going 85-90 KMH (= 55 mph) on a road which started uphill, and then went down the rest of the way my DIC was down to 11.5 l/100KM which would be near 20.5 US mpg. (Mine is 05 LLY 3500)

When I filled the tank, however, the real consumption was nearer 13.8 l/100KM = 17 US mpg.

The DIC seems to give highly optimistic readings, leaning towards the actual current driving more than the real averages especially when recently reset.

I'm still hoping for some improvement after a few more KM's on it.