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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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  #11  
Old 01-08-2005, 01:41 PM
Lee_klm Lee_klm is offline
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Join Date: Nov 2000
Location: Rogers, MN USA
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I selected 19+ on Highway, but would need to qualify my answer as under 60mph driving. 70mph will keep me at 17, maybe 18 with the wind...
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  #12  
Old 01-08-2005, 09:55 PM
belcll belcll is offline
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Join Date: Dec 2004
Location: Idaho
Posts: 3
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Quote:
Originally posted by MPH:
I too have been a little dissapointed in the lly's mileage. driving home from the dealer it averaged 18.4, which I was impressed with, but it has never been that high since. Pulling a little two place snowmobile trailer, i was only seeing about 11 mpg. I put 305's on it right when i got it home. could this have affected it that much? It didn't seem to drop the LB7 that far.
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2004 GMC Duramax Crew 4x4 HD 285/75/16
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  #13  
Old 01-08-2005, 09:57 PM
belcll belcll is offline
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Join Date: Dec 2004
Location: Idaho
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oops, did a false post. I added 285/75 tires and notice my mileage fall almost immediatly by about 1-2 mpg.


Quote:
Originally posted by MPH:
I too have been a little dissapointed in the lly's mileage. driving home from the dealer it averaged 18.4, which I was impressed with, but it has never been that high since. Pulling a little two place snowmobile trailer, i was only seeing about 11 mpg. I put 305's on it right when i got it home. could this have affected it that much? It didn't seem to drop the LB7 that far.
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  #14  
Old 01-13-2005, 03:27 PM
Freeman777 Freeman777 is offline
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Join Date: Aug 2004
Location: Las Vegas, NV
Posts: 20
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I participated in this survey (15 - 16 mpg city and 17 - 18 mpg hwy) a day or so after the poll was posted. I've been back several times since and noticed that the majority of the LLY owners fall into this category. I've been in the high 18's on several occasions, but didn't feel justified in voting in the 18 - 19 mpg class. Yesterday, on hwy #95 (just North of Las Vegas, NV) I ran a test under ideal conditions of road, wind, terrain, etc. and marked 20 miles at 70mph on the cruise control. The result was: 23.2 mpg according to my digital information center. My rig is a 2004.5 GMC C3500 CC, SLT, LB, 4WD D/A (LLY). After 6 mo. of use I now have 15K and the only thing I've been doing differently is using a fuel additive: Power Service -8 oz. per 25 gal. (states on the container: "absolutely no alcohol") Although this truck is running GREAT! I wasn't happy pulling a 36', 14+K, 5er over Baker grade (I-15 bet. Stateline, NV and Baker, CA) in 2nd gear, at 35mph at 3,500 rpm and both temp. gauges too close to hot for my comfort. Trips like that to San Diego resulted in 10mpg. Since my last trip, I've been anxious about the new Bank's set-up (in R&D for quite some time) for my LLY and got the GOOD NEWS call today: A six stage system (air filter, six-gun controller, exhaust system, boost and pyrometer gauges) that will selectively and progressively boost my engine/trans 128 HP and 345 fp torque. Stage #1 is the stock setting and every stage thereafter = a 20% boost. By going with the unique design of the Banks set-up, I think my engine/trans plus my 100,000 mi. after-market warranty will be better protected.
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2004.5 GMC 3500 SLT (All options) D/A SRW CC LB 4WD, Reese 20k fifth wheel hitch and Prodigy brake controller, factory toneau cover, Rhino liner, polished Aluminum wheels, Rotella T 5w40 synthetic. Banks Six-Gun bundle w/ Speed loader, Monster exhaust and pillar post guages.
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  #15  
Old 01-17-2005, 04:01 PM
eagle in flight eagle in flight is offline
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Join Date: Nov 2004
Location: NC
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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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  #16  
Old 01-17-2005, 05:03 PM
fishhead1076
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At first very disapointed with the lly and fuel milage, my average was around 12 no matter what towing or mt. After 12K and first fuel filter change my milage changed drastically, went from avg. of 12 to 17 in the city and 18+ on the highway. Didnt really buy into the break in better fuel milage bit, but I must say I was suprised.

My 2 cents...
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  #17  
Old 01-23-2005, 04:01 PM
tanker tanker is offline
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Join Date: Feb 2001
Location: Collegeville, Pa
Posts: 1,479
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Well just picked mine up last Monday night, did some round town back and forth to work running, then stretched its legs down to Virginia this weekend and the computer says 16.6mpg, not so bad running 70mph, Opps not supposed to go over 55mph in the first 500 miles, but ran well, didn't do any major acceleration's just cruised along with traffic. Should improve as it breaks in. First 100+ miles in stop and go driving, some high idle warm-ups. Will wait and see. Can't wait to hitch up and go.
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"Tankers-ToyII" Loaded 05 D/A K-3500 CC, SRW. Deep pan on Allison w/Transyn. Edge Juice w/attitude, 4" Kennedy exhaust, 98 Gal. Transfer-Flow cross bed fuel tank, Leer 100XQ bed cap. Reese 14,000lb class V hitch w/ dual cam HP sway control. Tow 34ft. 32FKD Holiday Rambler travel trailer. GCW 20,360lbs
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  #18  
Old 02-02-2005, 03:24 PM
jogger jogger is offline
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Join Date: Aug 2004
Location: North Carolina
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Did a short 150 mile round trip consisting of mostly freeway and rural driving and averaged 21MPG for that trip. In the city I average about 18.
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  #19  
Old 02-06-2005, 10:14 AM
guerrero guerrero is offline
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Join Date: Jan 2005
Posts: 13
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First 430 miles coming back from the dealer in Kellogg Idaho with outside temps hovering in the high 20's and several inches of snow on the ground through one of the mountain passes requiring prudent use of 4WD on I-90, averaged 20.5 mpg. Very happy with these results and expect additional improvements when I get the truck back to PH Hi and the warmer climates.
2005 PDN extended cab
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  #20  
Old 02-06-2005, 08:30 PM
mjammer mjammer is offline
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Join Date: Jan 2005
Location: Indiana
Posts: 89
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I am seeing 17.1 for mixed driving on my new truck, 2500HD D/A 4WD CC LB (just picked it up Friday) in the first 200 miles. That is better than I ever saw on my old gas 2500 extended.
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