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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.

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Old 05-17-2012, 05:49 AM
chessy56 chessy56 is offline
Join Date: Jan 2006
Location: South Milwaukee, WI
Posts: 230
Wink mileage

From these posts, it sounds like a new LML's fuel mileage isn't too far off of what I was getting when my LB7 was "new"- about 15-17 combined C/H driving. After a good break-in period, my mileage began climbing. It's now got 270K on it and frankly, mileage has become a reflection of just how heavy my right foot is! The LML, as I see advertised, is supposed to get better fuel mileage than its predecessors, but my LB7 will get (empty) ~21 mpg (highway) at 65-70 mph. Back that speed down to ~57 mph and I get better than 25- no B.S.!!!

Once these new LMLs are "broken in", I wouldn't be surprised to learn of highway mileage in the 20s. The biggest challange for any driver is having the "patience" to drive at reduced speeds.....
So. Milwaukee, WI
'01 2500HD, LB7, 440K miles
"Stock" engine. Dual fuel filtration system with Kennedy lift pump, BF Goodrich Commercial T/A Traction tires (sold to a dude from Texas- it's living a warmer life just fine down there now!).

'17 2500HD, L5P (Happy Birthday/Merry Christmas to me!!!) Currently bone stock, 90K miles.

"Socialism is a philosophy of failure, the creed of ignorance and
the gospel of envy. Its inherent virtue is the equal sharing of misery."
Winston Churchill
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Old 07-08-2012, 09:48 PM
ChevysRus ChevysRus is offline
Join Date: Sep 2001
Location: Brentwood, California USA
Posts: 497
Default 2012 2500 Duramax

Just picked up my new truck, also my 3rd Duramax. Had a great '01, better '07 and hoping this one is a great '12. Had 9 miles on it when I picked it up, drove it about 50 miles around town and hooked up my 28' Haulmark (empty) and drove 850 miles from Seattle to San Francisco to break it in LOL. Averaged 13.2 MPG right out of the box.

Headed back in 2 weeks with the car trailer loaded with my '57 Chevy for GoodGuys Puyallup Car show. My '07 got 13-15 MPG towing loaded and 17-18MPG around town, no trailer. Expecting same or better from this new truck. I do like all the improvements with or without better mileage.

I sold the '01 at about 75K and traded in the '07 same at 76K. Great trucks, just higher value trading early every 5-6 years.

If you can afford one of these great trucks, don't worry about mileage, diesel today is a buck cheaper than it was 4 months ago. Enjoy it while it last LOL. These trucks get you where you are going faster, safer and with more comfort than we really need. The braking, tow/haul and the new exhaust braking all results in less white knuckle adventures as well.

With my favorite car in the box and my family and grandkids in the cab, I want a truck that is big time overkill for the job at hand. Duramax gives me that confidence. Many years ago I did same towing with a 1500 gasser. Talk about being on the edge of disaster all the time. Young and foolish back then.

Anyway, just enjoy the trucks and don't sweat the small stuff.
\'01 Chevy EC/2WD/SB, T/F 45 gal, Delvac 1, TranSynd, deep pan, MAG drain plug. Escalade handles & painted bumper capto. After market grill, billet bowtie, Stockland cover, no side trim, no juice, no gauges, nuttin but stock! Nicktane Big CAT Pre-OEM. Gone, but not forgotten.

'07 Crew Cab LBZ stock all the way except added 45 gallon Transfer Flow tank and billet grille. Great truck also now gone, but not forgotten.

'12 Crew Cab stock for a few more days LOL

Last edited by ChevysRus; 07-08-2012 at 09:58 PM. Reason: updated signature
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Old 05-30-2013, 09:53 PM
ceide4489 ceide4489 is offline
Join Date: May 2013
Location: Canada/Alberta/Rocky
Posts: 6

I have a 2013 2500HD and when I purchased it I manually checked cause the truck said I was getting 19.5 and I am getting this when done by hand. I have recently put a BDS lift in with 35" mud tires and am getting 18MPG

When towing my small holiday trailer under 5000 pounds I get 14-15MPG

These numbers are considerable better than the 2011 I had prior to this and not really sure why. I didnt think they changed anything
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Old 07-28-2013, 03:29 PM
kelloso kelloso is offline
Join Date: Jul 2013
Location: Texas
Posts: 3
Default LML Mileage

I own a 2011 GMC 2500HD LML and I am getting 20-22 empty, 13 if its in REGEN. Towing my TT I am getting around 12-15 on flat ground running 60. Thinking about trying that Dura Mileage for the LML, claims 4-7 MPG empty running the 90HP tune. Any thoughts?
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Old 07-30-2013, 06:37 AM
GM Customer Service's Avatar
GM Customer Service GM Customer Service is offline
Join Date: Aug 2012
Location: Michigan
Posts: 48

Y'all can check out for some extra tips on how to save on fuel! Every little bit helps these days. Happy travels,

Kelly J.
GM Customer Care
For information on the GM Privacy Statement, please visit
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Old 09-04-2013, 07:50 AM
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dougmac dougmac is offline
Join Date: Sep 2013
Location: Washington State
Posts: 12

My 2013 LML: 20.5 on the highway, 15-17 around town, 11.5 towing my 5000 lbs travel trailer over in the mountains. (checking manually... the DIC is a little more optimistic than the actual mileage)
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Old 11-17-2013, 09:33 AM
Waynec1957 Waynec1957 is offline
Join Date: Nov 2013
Location: Central Indiana
Posts: 5
Default New 2103 CC

I just picked up my new (first ever) 2013 CC Duramax this week. Our camper is about 5,000 lbs empty and If I can get those kind of numbers...I'll be tickled to death.
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Old 11-22-2013, 05:02 PM
Waynec1957 Waynec1957 is offline
Join Date: Nov 2013
Location: Central Indiana
Posts: 5
Default LML Mileage

Just did the first fill up (22 gal/320 miles) on my new LML. 14.5 combined city/highway (about half and half). Conservative estimate hwy...what, 18 maybe? No towing, just empty. Not too bad out of the box...I was expecting a lot less. My old 5.3l vortex got a combined 18.5.
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Old 07-13-2016, 07:27 AM
philstat philstat is offline
Join Date: Jul 2016
Location: WI
Posts: 1

Originally Posted by Dinkie Diesel View Post
I'm in the market and would like to see some real world reports on mileage. All I have found so far is predictions and outlandish claims. Maybe there's not that many owners of 2011s here yet to report?
bought new 15' 2500HD last August; now have 23000m, about 85% towing a 3 ton TT cross country. So far avg. mpg towing is about 12. Ranges from 10 to 17 depending on wind. Crossing the mtns. is not an issue; acutally get mileage above 13. It's the wind on the plains that knocks back the avg. The 30' trailer is 11' tall, and it's like towing vertical sheets of plywood down the road.
Am picking up a new fiver (5 ton) next month in WA. will keep posted what new mileage is. Trailer is taller, but has "aerodynamic" cap in front, whereas now I have a wall of fiberglass on my TT.
Diesel is awesome, as they say "you'll never go back"

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