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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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  #111  
Old 01-24-2013, 12:57 PM
AKMark AKMark is offline
Building another 6.2L powered vehicle
 
Join Date: Dec 2006
Location: North Pole, Alaska
Posts: 400
Default

05 LLY, CC, LB 94K miles, 15K hours, unknown age of injectors, runs great though.

In Alaska with temps in the -20 range, 15 driving approx 14 miles one way twice a day every day. (56 mph, if I drive 60 this drops to 13)

17 over a 85 mile drive with 3 hills over 8 degrees of upward angle. (67 mph)

This is with #1 Diesel, mixed with 2 stroke oil.

I haven't taken it on any longer road trips yet, and unfortunately all of our roads out of Fairbanks will encounter big hills.
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05 2500HD CC LB LLY, 4x4, 3.73s 235/85R16's, webasto cab heater, to keep it warm.
03 Buick Rendezvous - When you average over 80 miles per day driving around, you need one of these.
85 K-5, 6.2, SM465, Rockwell T221, 1 tons, 36's. More goodies to be installed as time and money allows.
82 K20, 6.2, SM465, NP208, stock except for bed rack, snow plow, and glow plugs are on a toggle switch. It works great for plowing!
72 Postal Jeep - Yet another project
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  #112  
Old 02-24-2013, 11:00 PM
gary_lucas's Avatar
gary_lucas gary_lucas is offline
Enthusiast
 
Join Date: May 2012
Location: Langley
Posts: 372
Default

Had the truck for almost a year now, put about 12k on it.

Overall thinking it's a great truck, but the fuel economy is less than I hoped for.

My last set of numbers put me in the 14.2mpg range with mostly city driving unloaded.

When I got the truck last year it had:
* Modified exhaust (Not sure what it is, going to find out tomorrow).
* Edge Juice with Attitude.
* p265/75's

I've removed the attitude module this evening for the first time. I had a bakflip installed this past week and I'm going to get a Kennedy tuned ECM for our trip down to Las Vegas next month. We'll be hauling a 3200lb trailer so I'll get a good idea of the mileage at that point.

My understanding of how to drive with fuel efficiency in mind basically starts and ends at takeing it easy, don't floor it to get up to speed, Keep it at the low end of the speed spectrum (IE on the highway keep it towards 55 rather than 70 if at all possible...)

When the current 265's start getting old I'll probably replace them with the stock 245's and hope to see some better fuel economy.
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GMC Sierra 2500hd 2004.5 now with ARP studs
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  #113  
Old 04-07-2013, 02:43 PM
gary_lucas's Avatar
gary_lucas gary_lucas is offline
Enthusiast
 
Join Date: May 2012
Location: Langley
Posts: 372
Default

Followup, just drove from Vancouver BC to Las Vegas Nevada and back up the I-5 in California.

Combined average of about 17.5MPG the whole way. I was towing a 3000lb trailer with a really low profile (low wind resistance).

I was getting close to 19MPG on the I-5 on the way back, going through the mountains brought it down to 17.5 approximately.
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GMC Sierra 2500hd 2004.5 now with ARP studs
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  #114  
Old 03-04-2014, 04:02 PM
AKMark AKMark is offline
Building another 6.2L powered vehicle
 
Join Date: Dec 2006
Location: North Pole, Alaska
Posts: 400
Default

First long road trip with my 05 this last weekend.

734 miles driven (per gps). I have an 80 gallon external tank in the bed that keeps the main topped off. It took 35.7 gallons to top off the external after we got home and I confirmed the main was full.

20.7 mpg, I drove 67mph (per gps) except for about 200 miles on the way back when I stepped it up to 72mph to keep up with a convoy of friends.

Considering my motor has over 16K hours on it, I'm happy.
__________________
05 2500HD CC LB LLY, 4x4, 3.73s 235/85R16's, webasto cab heater, to keep it warm.
03 Buick Rendezvous - When you average over 80 miles per day driving around, you need one of these.
85 K-5, 6.2, SM465, Rockwell T221, 1 tons, 36's. More goodies to be installed as time and money allows.
82 K20, 6.2, SM465, NP208, stock except for bed rack, snow plow, and glow plugs are on a toggle switch. It works great for plowing!
72 Postal Jeep - Yet another project
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  #115  
Old 05-23-2014, 06:23 PM
dfenze dfenze is offline
Newbie
 
Join Date: May 2014
Location: San Diego
Posts: 3
Default

04.5 LLY with 110K miles. When new I was getting 18-19, no matter what I did. now, I get around 15-17. I have some upgrades, but I am also having a lot of issues with the motor right now.
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  #116  
Old 06-18-2014, 10:53 AM
AKMark AKMark is offline
Building another 6.2L powered vehicle
 
Join Date: Dec 2006
Location: North Pole, Alaska
Posts: 400
Default Summer update

Tried a different fueling place. Glad I did.

Running short trips (14-18 miles at a time usually) I'm averaging 18-20 with summer weight fuel and a little bit of 2-cycle oil to give me some lubrication.

I haven't had a long road trip since using this stuff, and my bad luck I will be back to winter fuel before long. Summer doesn't last long here.

I found two of the other stations I used to fill at run winter fuel all year round. Jerks.
__________________
05 2500HD CC LB LLY, 4x4, 3.73s 235/85R16's, webasto cab heater, to keep it warm.
03 Buick Rendezvous - When you average over 80 miles per day driving around, you need one of these.
85 K-5, 6.2, SM465, Rockwell T221, 1 tons, 36's. More goodies to be installed as time and money allows.
82 K20, 6.2, SM465, NP208, stock except for bed rack, snow plow, and glow plugs are on a toggle switch. It works great for plowing!
72 Postal Jeep - Yet another project
Reply With Quote
  #117  
Old 01-07-2017, 01:37 PM
Rhynno's Avatar
Rhynno Rhynno is offline
Owner Duramax 6.6 LLY & 7.3 Powerstroke
 
Join Date: Jan 2017
Location: USA, Oregon
Posts: 1
Default Not Impressed With MPG

I have had my 2005 GMC 2500HD Duramax for over a year now, and it gets horrible fuel mileage. It is lifted with 35" tires, has an aftermarket air intake system, Edge Attitude chip, and aftermarket exhaust (not sure on the gears, assuming stock). I get between 10.5 and 11.5 MPG. At first, I thought it was the chip because it was set to Stage 3 and had tons of power, so I changed it to Stage 1, the economy setting. I only gained .5 MPG, so I changed it back to Stage 3 to get the 70hp and the 120 Ft. lbs. of torque. I also have a 2000 Ford Excursion 7.3 Powerstroke which I have owned for 14 years. It is much heavier than my Duramax, especially when the 44-gallon fuel tank is full. It has a 6-inch lift, is running 37" BFG KM2 M/T tires, and the gears are stock. For the life of the Excursion, I have averaged 17.3 MPG around town and I have even been able to achieve 20.4 on the highway, loaded down with camping gear and people. The big difference I see between these vehicles is the Excursion has hubs and the Sierra doesn't. I haven't had a lot of time to work on the Sierra, so I am sure I will be able to tweak it some once I can spend a little time and money on it, but I was hoping it would at least deliver 15 MPG around town. I hope to get one of the hub conversion kits from the Ram Man this year and get that installed to see what difference that makes, but at this point, I have just done routine maintenance. I will also give it a tuneup when time allows. Love the truck though, drives awesome, very comfortable and get amenities!
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  #118  
Old 10-29-2018, 12:13 PM
wmholden wmholden is offline
Newbie
 
Join Date: Oct 2018
Location: San Antonio Texas
Posts: 3
Default Still Bone Stock LLY

In 2005 I averaged 21.7 mpg on a trip from Texas to Savannah @ 67.5mph. Last week I averaged 18.5 over an 800 mile trip, half of which include about 1200 lbs of hickory in the bed and 70-75mph. So I have no complaints. I love my LLY. And since I now live in town(again)my city mileage is 13.5 to 13.9 mpg. We are looking at the DT400 performance package now. We are approaching 160K and are ready for mods.
DT400 components for under $800 total look like a nice foundation for performance- now and future. I hope to find reviews on the DT400 kits

Last edited by wmholden; 10-29-2018 at 12:16 PM. Reason: Miles on Truck
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