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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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  #21  
Old 02-07-2005, 04:11 PM
Mile Hi Guy Mile Hi Guy is offline
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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?
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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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  #22  
Old 02-10-2005, 03:07 AM
Shire Ben Shire Ben is offline
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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
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  #23  
Old 02-23-2005, 01:41 PM
pepper pepper is offline
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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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  #24  
Old 02-24-2005, 03:51 PM
Dewey Faircloth's Avatar
Dewey Faircloth Dewey Faircloth is offline
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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.
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1994 GMC 2500 Suburban 6.5 TD 210,000 miles.
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  #25  
Old 03-18-2005, 06:15 AM
Jerry D Jerry D is offline
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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.
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  #26  
Old 03-18-2005, 10:26 AM
Curt B. Curt B. is offline
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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.
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  #27  
Old 03-21-2005, 06:08 PM
KCDuramaxTurbo KCDuramaxTurbo is offline
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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.
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  #28  
Old 03-22-2005, 12:00 PM
Noal Noal is offline
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'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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  #29  
Old 04-08-2005, 08:00 AM
Shoe Shoe is offline
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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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  #30  
Old 04-17-2005, 06:25 PM
Wally1 Wally1 is offline
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05 CC/4X4. About to fill up for my third tank.
So far 13.4 mpg all city driving.
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  #31  
Old 04-18-2005, 04:13 AM
mjammer mjammer is offline
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Wally, that is similar to what was seeing except a little lower as it was cold weather in February. Find an excuse to take a couple of log interstate trips to help break it it at more than just highway sppeds and see what it does on the interstate. My local driving mileage has seemed to pick up after some longer trips and the associated mileage. I am at 2500 miles now and see low 18's on interstate running ~68-69 MPH. My local mileage has picked up 1-2 mpg now.
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  #32  
Old 05-03-2005, 05:47 PM
JD Diesel
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2000 on LLY 14 t0 16 Lot better than my 2500 sub with 454 vortec 9 to 11
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  #33  
Old 05-09-2005, 12:48 PM
reedpilot reedpilot is offline
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I have a brand new 2005 2500HD with almost every option and I am getting 15.8 around town and 21.9 on the hwy. What are people using to increase fuel economy?
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  #34  
Old 05-09-2005, 06:16 PM
AndyU
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I took delivery March 31. I have about 3500 miles on already. I get around 17 in the city and as much as 21 highway, unloaded. Average unloaded highway mileage at ~75mph is between 17 and 20 with wind conditions making a big diffence. With a tail wind I will break 20. With a head wind... 17. Same pattern pulling my gooseneck horse trailer. Anything from 8.5 to 11.5 depending upon wind conditions at 65 to 70 mph. The trailers pretty big and heavy though, 8' wide about 9' high x 34' long, fully enclosed aluminum and stainless steel. 2-3 horses, water and hay add another 2-3 thousand pounds.

I just bought a Predator and on Sunday I loaded the 40hp tow program. I pulled my horses on a little 160 mile trip and the DIY said I got 11.8 pulling into a head wind @65-70 mph. Not bad I thought.. about 2 mpg better than usual into a stiff headwind. Next I unloaded two horses and reset the DIY. I then pulled my empty trailer another 40 miles down back highways at 55-60 crossways to the wind. It said I got 16 mpg. AWESOME! I thought (about 4mpg better than usual!). Finally, I dropped the trailer, reset the DIY and ran another 40 miles with the just the truck at 75 (no wind by then) and the DIY said I averaged 25mpg... that's when I got skeptical... to good to be true. I drove to work and back today, another 20 miles (I usually get about 17 to work and back). I refilled the tank and it took 21 gallons. 260 total miles / 21 gallons = about 12.4 average mpg. That was obviously way off. It should have used about 18.7 gallons according to the DIY for around 13.9 average mpg. The DIY used to be accurate within about 1/2 mpg and usually showed less than my actual. Now it's way off the other way. Despite the impressive computer reports, my real fuel economy appears no better...

Does anyone know why the DIY would get so far off? Does the predator change the calculations?

I'm going to continue testing for another week. If the predator provides no improvement over stock economy, it's going back. If I can get an extra 1 mpg or better, then it's well worth it, especially since it won't over stress my truck. The simple 40 hp tow program is as hot as I care to get.

I really baby the truck when I'm driving, soft stops, soft starts, rpm never gets above 2500. I really drive to maximize my fuel economy and equipment life.

Has anyone else seen improved fuel economy with a programmer? I have a friend who gets 23 with his 05 stock cummins and 15 pulling a trailer like mine. I'm on a real quest to get similar performance.
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  #35  
Old 05-10-2005, 08:24 AM
okeehandyman
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have 2 '05 2500HD 4x4, 1 c cab 6' box & 1 ex cab 8' box. both getting 17-18 intown & 21-22 on out of town trips around 60 mph. about 1.5 mpg less per 10 mph faster. the fact is you have to decide how fast vs how much fuel to use. no free lunch, remember.
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  #36  
Old 05-24-2005, 10:08 AM
AndyU
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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.
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  #37  
Old 06-16-2005, 06:47 AM
57CHEV 57CHEV is offline
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I consistently got 16 with my 02 LB7 and 14 with my 04 LLY all in town driving. Exact same trucks except one was a Chevy & one was a GMC.
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  #38  
Old 06-21-2005, 04:11 AM
bamabadboy bamabadboy is offline
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19.8 MPG on a 800 mile trip. Unloaded, all stock, air on, driver only, bed uncovered, 65-70 MPH all the way, 271 miles on the odometer at start.
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  #39  
Old 06-21-2005, 11:40 AM
Shorty Shorty is offline
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Purchased 2002 HD 2500 DA crew cab in Jan 05 LOVE THAT TRUCK getting 18 average empty around Texas.Came to Colorado towing 28ft. Jayco got 12mpg towing trailer. purchased Predator installed 2nd highest economy tune getting 20 mpg average.went from Grand Junction to Ft. Collins about 600 miles average 21 mpg best I have done so far. Haven't tried towing yet. EGT got around 1200 going over Vail and Loveland passes had to ease off of cruise to maintain EGTs
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  #40  
Old 06-23-2005, 02:00 PM
RodneyRam-jet RodneyRam-jet is offline
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I picked up my '05 K2500HD CC SB 6/13/05. Used 18.895 gallons to go first 270 miles. I will fill up tonight or tomorrow on second tank full. That puts me at 14 mpg on first tank and I can tell I am doing better on second tank. Taking my first trip towing in two weeks. Does anyone use fuel additives? Any recommendations? I heard it's good to use during break-in.
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