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Duramax 6600 Welcome to the Internet's first Duramax 6600 diesel discussion forum for the LB7, LLY, LBZ, LMM, LML, LGH & L5P RPO code engines. Tips on performance, fuel economy, troubleshooting and more.

View Poll Results: 2004.5 or newer LLY Duramax local driving fuel economy
less than 15 mpg (US gallons) (55-65-mph) 454 41.58%
15-16 mpg 163 14.93%
17-18 mpg 165 15.11%
19-20 or more mpg 220 20.15%
Don't own an LLY - just wanted to see poll data 90 8.24%
Voters: 1092. You may not vote on this poll

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  #41  
Old 06-23-2005, 04:05 PM
G Slaton G Slaton is offline
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I have an 05 CC 2wd Duramax/Allison. This is my fourth Duramax. By far the 03 got the best fuel mileage and ran just about as good as the LLY. I hae driven several LLYs and all run better than mine, local diesel tech says it happens and no real reason why. Running at cruise control 70 It will get a best of 14.7 and a headwind will knock it down below 14. I dragrace and tow a 42ft enclosed gooseneck hauler(14,000#). Normal mileage is 8.9 towing 67 mph.. Headwind will take it below 8.0 I check all fuel mileage by filling to the neck and useing the trip odo. The truck indicator is usually within .1 to .2 mpg of the actual. This truck has 20,000 miles on it and the fuel mileage has not improved with age as I have towed with it from 500 miles on. The LLY has been a bit of a disappointment. I have owned Chevy trucks all my life and am not about to change but this particular truck is not the best one I have ever owned. My LB7 trucks would get 10 towing the same trailer and have been as high as 11.5 on no wind level ground.

Gary
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  #42  
Old 06-24-2005, 12:09 PM
LJ LJ is offline
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Hey guys, this is my first post, my first diesel pickup, and so greetings to all.

My truck is a 2005 2500HD w/ Duramax bought 6/1. The first 1,000 miles, the DIC said I got 17.4 overall. When it turned over 1,000, I reset it. Since then, overall, it's been 19.1.

Good points on slowing down above. That Allison tranny won't let me coast. I can see that driving habit changes will help.
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  #43  
Old 06-27-2005, 09:03 AM
6APPEAL 6APPEAL is offline
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Purchased a 2005 Chevy 2500 HD Crewcab Duramax/Allison 2wd on 6/18. Just about ready to fill up my 1st tank and have been getting between 16 and 17 mpg according to the DIC with mostly city driving. I'll manually check that upon filling up to see how close the DIC is. I've been taking it easy, staying under 2500 rpm. Taking a trip this weekend and should be above the 500 mile mark listed in the owners manual, so I'm curious to see what kind of milage I'll get with all highway driving around 70 mph. This is my 1st diesel, which I bought for the towing capabilty. But, I will say it's getting within 1.5 mpg of my old 4.8l C1500 extra cab for the same daily work/home driving. Should exceed the gas burner while towing and not be as hairy to drive.
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  #44  
Old 06-29-2005, 03:59 AM
6APPEAL 6APPEAL is offline
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1st tank of fuel last night. Figured my mileage (361 miles on 19.61 gallons), 18.4 mpg. All I can say is WOW. The DIC was off about 1.5 mpg, but who cares. That is the same mileage I was getting with my 4.8 gas burner in the same driving conditions. I'm interested to see if it get the same on a road trip. The gas burner would get around 23 (70+, air on, unloaded). I know the diesel will blow it out towing.
John
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  #45  
Old 06-29-2005, 12:30 PM
dieselmaybe dieselmaybe is offline
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Just bought a new Chevy 2005 2500HD LT Duramax/Allison yesteday. Had 3 miles on it when I left the dealer. I reset the DIC after driving home, about 25 miles, and checked it with the cruise control set at 60mph, it climbed to 18.5 after about 10 miles. How accurate is the DIC reading? Just curious, I intend to refill the tank and check it the old way this weekend. I test drove the Ford and Dodge and liked the Chevy best. This is a very nice truck. Also, I have noticed a lot of discussion about tire size. The dealer where I bought mine has 265/75s on his demo and said he thinks it lowers the power and fuel economy but shouldn't hurt anything or affect the warranty. I would really like to upgrade these 245s to 265s but don't want to lose much fuel economy, any opinions would be appreciated. (It doesn't seem like a 3.6% increase in diameter should have much effect)
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  #46  
Old 07-03-2005, 05:18 AM
dieselmaybe dieselmaybe is offline
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Checked the unloaded mileage the old way on my new 2005 Chevy D/A. In town, 100 miles 13.8 mpg. 200 mile highway trip Saturday, driving fairly easy 55-65 mph it got exactly 19 mpg. The DIC was fairly accurate also. It was saying 13.5 in town and 19.5 on the highway. I also upgraded to Cooper Discoverer ATR 265-75 E rated tires. I couldn't stand those little 245 tires . Speedometer is off a little, at 60 mph my GPS says 61.2 mph. Before changing the tires the GPS read 59 when the speedo read 60. I'm liking this truck more every time I drive it.
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  #47  
Old 07-04-2005, 12:50 PM
Bill W Bill W is offline
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I have a new 05' extended cab regular bed. with 300 miles on the truck I am getting 14.5 on the city, 21 on cruise control at 60 mph per the display
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  #48  
Old 07-14-2005, 12:07 PM
VANBC2500HDDA VANBC2500HDDA is offline
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I just got a new 2005 Dually Crew SLT 4x4, and so far the trip computer is scaring me, average is 10MPG....

Does the mileage really fall off on the 1 ton trucks?

My last truck was a 2500HD
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==============================================<br />Stephan Mackenzie, B.C.<br />2001 CK2500HD DA SB EXT Black/Tan Loaded<br />2003 Volvo XC Wagon Loaded<br />2002 Carriage Cameo Lxi 33ft 5th Wheel<br />1996 Camaro SS 396LT4 6SPD 500HP Red/Black<br />2000 Honda RC51 Twin
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  #49  
Old 07-15-2005, 03:14 PM
cruzar cruzar is offline
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I just received my 2005 2500 hd 6600 and took it for a road trip kept it at 65 - 70 and if the computer is correct it was steady at 18.9 and on the ranch with hills and draws in 4 wheel it was at 17.8 I am pleased at this time.
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  #50  
Old 07-20-2005, 11:03 AM
bthompson bthompson is offline
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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?
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  #51  
Old 07-24-2005, 01:32 PM
cruzar cruzar is offline
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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.
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  #52  
Old 07-24-2005, 05:11 PM
Kelly T Kelly T is offline
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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
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  #53  
Old 07-29-2005, 04:44 PM
Black95TD Black95TD is offline
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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.
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  #54  
Old 08-03-2005, 06:40 PM
Steve Rapp Steve Rapp is offline
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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.
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  #55  
Old 08-04-2005, 04:45 AM
fourtenposi
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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.
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  #56  
Old 08-06-2005, 04:48 AM
cruzar cruzar is offline
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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.
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  #57  
Old 08-15-2005, 02:40 PM
daleslad daleslad is offline
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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.
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  #58  
Old 08-20-2005, 12:08 PM
dieselfish dieselfish is offline
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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.
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  #59  
Old 08-28-2005, 01:04 PM
Kelly T Kelly T is offline
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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 ]
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  #60  
Old 09-05-2005, 06:03 PM
cruzar cruzar is offline
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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.
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