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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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Old 02-07-2005, 04:11 PM
Mile Hi Guy Mile Hi Guy is offline
Join Date: Apr 2004
Location: Denver, CO
Posts: 11

Well I have roughly 17,000 miles on her now I got 16.0 twice (I do check every tank manually) but usually average low 15's empty driving mostly a 80% Hwy commute. Traded my brother one week (10 days actually) and got 17.2 doing the same routine in a 2001 AWD Denali

Truck runs ok but not nearly as strong as by Brother-in-laws 05 CCSB Ford 6.0

Had the truck in twice and they say everyting is ok in the motor department. The only thing they cannot seem to fix is the Drivers seat will not keep it's memory and a whistle on the passenger side door. Would that qualify for a lemon?
2004 SBCC LLY, Alli, SLT, XM, DVD, Roll-N-Lock, Power Lock Tail Gate, Luvern SS Bars, 45 gal Transfer Flow Replacement Tank
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Old 02-10-2005, 03:07 AM
Shire Ben Shire Ben is offline
Join Date: Feb 2005
Location: North Brookfield, Massachusetts
Posts: 23

I have a 2004.5 LLY which I purchased in Mar 04 with 24K and I consistently get 19 mpg hwy. No modifications or upgrades. LOF every 3K and FF every 15K. Had similar experience with 2001 LLY which 85K, same maintenance, no injector problems..Thanx
2004.5 2500HD Dmax/AT extended cab SB.
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Old 02-23-2005, 01:41 PM
pepper pepper is offline
Join Date: Feb 2005
Location: va beach,va
Posts: 6

I have gotten 22 mpg on a tank full but I had to keep my foot out off the accelerator, 62 mph or slower and no repeat no hard acceleration, that is no fun so usually hit a few times per tank and get 18-19 - towing the boat i get 13-14 it is a wide flats boat with center console which is more of a wind trap than a weight issue, heck i only got 12-13 highway with my old gas van, wish they had a van with this eng/tran setup. I'd have one tomorrow, yes w/4wd!
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Old 02-24-2005, 03:51 PM
Dewey Faircloth's Avatar
Dewey Faircloth Dewey Faircloth is offline
Join Date: Mar 2000
Location: Mobile, AL U.S.A.
Posts: 28

Get 18 to 19 driving empty 13.2 pulling travel trailer staying about 65.
Leaving Saturday going to Camp Lejuene pulling trailer and will see if it does better now has over 12,000 miles on it,fresh filters and gravy.
2005 Chevy 2500 HD Duramax CC SB 30,000 miles.
1994 GMC 2500 Suburban 6.5 TD 210,000 miles.
1983 Mercedes 300 D Turbo Diesel 150,000 miles.
1991 Holiday Rambler Aluma Lite XL 30 foot.
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Old 03-18-2005, 06:15 AM
Jerry D Jerry D is offline
Join Date: Apr 2004
Location: Harwinton, CT
Posts: 8

Today's 50 mile journey of back roads and HW had me average 22 MPG according the DIC. I'm wondering if when I filled up a couple of days ago I got my first tank of Non winter fuel because this is better than I've been getting recently.
2004 LLY CC-just plain stock (for now)
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Old 03-18-2005, 10:26 AM
Curt B. Curt B. is offline
Join Date: Sep 2004
Location: Sterling, CO
Posts: 6

Just wondered how fast most of you drive, that are seding 18+ mpg? I drive 75-80 on interstate most trips, and I have yet to get over 17. Today with 30 mph tailwind, DIC was showing 20-21. I never get that on a normal trip.
2005 GMC Sierra 2500HD CC SB, D/A<br />Juice with Attitude, Kennedy 4\" exhaust, AFE Stage 2, Boost Stick
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Old 03-21-2005, 06:08 PM
KCDuramaxTurbo KCDuramaxTurbo is offline
Join Date: Mar 2005
Location: KC
Posts: 12

300 miles so far 05 lly, first tank, home from dealer 20.0, now 18.2. Really easy on the accelerator. Have a predator coming.
05 GMC Ext Cab 2500 HD 4x4 LLY/Allison<br />Predator<br /><br />Formally 2002 Chevy 2500 LT 4x4 Ext Cab, LB7 Hot Juice/Predator
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Old 03-22-2005, 12:00 PM
Noal Noal is offline
Join Date: Mar 2005
Location: Baytown, Texas
Posts: 7
Thumbs up

'05, 4x4 2500 HD Crew Cab. 3000 miles. Getting average or 16mgp town or highway. Had '02, same truck except 8.1 L gas. 60 % better milage. See the smile on my face.
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Old 04-08-2005, 08:00 AM
Shoe Shoe is offline
Join Date: Apr 2005
Location: Grosse Pointe, Mi
Posts: 3

First post on the forum...

I'm sure hoping my the mileage on my 05 will improve as it breaks in. I'm milking it in order to achieve anything over 17. (still under a 1000 miles) The 03 was getting a steady 19 from the dealer and ended up with 21 at 65K. Sure seems the turbo kicks in at a lower RPM on the new one and it runs a little warmer than the 03 at higher speeds.

Great Forum!
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Old 04-17-2005, 06:25 PM
Wally1 Wally1 is offline
Join Date: Apr 2005
Location: Rocky mountain southwest
Posts: 1

05 CC/4X4. About to fill up for my third tank.
So far 13.4 mpg all city driving.
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