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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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  #71  
Old 11-02-2005, 04:12 PM
AndyU
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Quote:
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.
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  #72  
Old 11-04-2005, 07:39 PM
REDTRUCK05 REDTRUCK05 is offline
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Join Date: Aug 2005
Location: HUGO, MINNESOTA
Posts: 126
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Quote:
Originally posted by Cliffee:
I'm averaging 16.5 with mostly short city trips. 1800mi on OD. 2005 LLY
how fast?
__________________
2007 GMC 2500 crew cab LBZ
6.6L duramax
Roof markers and XM radio
Rhino liner
Plat series nurf bars
Putco bed rails
Truxedo bed cover
edge juice W/ monitor temp uninstalled.
Hypertech stage 3
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  #73  
Old 11-04-2005, 07:54 PM
REDTRUCK05 REDTRUCK05 is offline
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Join Date: Aug 2005
Location: HUGO, MINNESOTA
Posts: 126
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Quote:
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
__________________
2007 GMC 2500 crew cab LBZ
6.6L duramax
Roof markers and XM radio
Rhino liner
Plat series nurf bars
Putco bed rails
Truxedo bed cover
edge juice W/ monitor temp uninstalled.
Hypertech stage 3
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  #74  
Old 11-06-2005, 06:17 AM
tboy76 tboy76 is offline
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Join Date: Oct 2005
Location: Louisiana
Posts: 1
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Quote:
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.
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  #75  
Old 11-09-2005, 07:59 PM
omercer omercer is offline
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Join Date: Oct 2005
Location: Ely, Nevada
Posts: 3
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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.
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  #76  
Old 11-10-2005, 10:58 AM
JohnC
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Quote:
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...
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  #77  
Old 11-15-2005, 10:16 AM
mad mad is offline
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Join Date: Oct 2005
Location: Pensacola, FLorida
Posts: 7
Cool

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!
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2005 LLY in 2500HD 2WD<br />4\" Magnaflow turbo-back exhaust<br />AFE Stage2 intake<br />Retrax bedcover w/LineX...and the list keeps growing!!!
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  #78  
Old 12-30-2005, 05:18 PM
JD Diesel
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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]
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  #79  
Old 04-06-2006, 08:44 AM
AndyU AndyU is offline
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Join Date: Mar 2006
Posts: 16
Default

Quote:
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.
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  #80  
Old 05-10-2006, 07:24 PM
Dannyboy Dannyboy is offline
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Join Date: Jan 2005
Location: NorthEast
Posts: 37
Smile 06 lly mileage

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!!!
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2006 Chevy 2500 HD Ext. Cab SB, LLY w/ Alli 6 speed
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