Duramax

Discussion in 'GM Duramax 6.6 (LB7)' started by chevytrucknut, Oct 8, 2005.

  1. chevytrucknut

    chevytrucknut Well-Known Member

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    Hey i got a 01 duramax with the allison im only getting 16 mpg i wondered what some of you other guys are getting and if you know of anything that could cause this poor mileage i heard they will get upwards of 20-21. but even with that complaint it pulls awesome i was towing two full grain wagons when combined weighed 15 ton and it hardly felt like a load was there. waytogo remember to be cummin you have to be strokin to be strokin you have to be hard as a rock :D
     
  2. RJF's Red Cummins

    RJF's Red Cummins TRC Staff Moderator

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    Gross and weird.....

    30K net really is too much for any pickup. Hope you aren't going far.

    You didn't mention what 16mpg was....in town? Freeway? Average of both? Seems all three brands are getting very similar mileage. 16 in town is good, 16 on the freeway at sensible and safe speed is a little low. 16 average is about average....
     
  3. PermanentMarker

    PermanentMarker TRC Staff Moderator

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    Agreed. On all counts.
     
  4. BadDog

    BadDog TRC Staff Staff Member

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    I personally think that those claiming "upwards of 20-21 mpg" are smoking something. You *might* manage a bit over 20 or so if you ran out a tank on I10 in texas at 55mph unloaded. Best I ever managed was "just under 20" (don't remember specifically, been a while), unloaded across I10 in Texas at night with the reduced night-time speed limit on 55psi 33s.

    I haven't even checked my mileage in a very long time. I tend to enjoy the power too much, and after adding the chip, it's just beyond my powers of restraint not to feel my stomach pressed into my backbone on most every acceleration. Anyway, these trucks are VERY RPM sensitive with respect to maximizing fuel efficiency. Seems to me the DMax like to run between 1800 and 2000 to maximize the fuel efficiency, and of course, air resistance increases dramatically with speed. Getting a 7000 lb truck moving is also a big job and will knock it down fast, it makes a big diff if you are real smooth and easy from the stop lights, slowing to avoid stopping at lights, and so on. So, if you want to compete in the fuel mileage bragging rights event, you're going spend quite a while in the slow lane with no fluctuations in speed and holding close to those rpms. Me, I would rather enjoy my truck...
     
  5. RJF's Red Cummins

    RJF's Red Cummins TRC Staff Moderator

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    I basically agree. Recently I did a 200 mile round trip that was 95% highway, 5% of surface streets to and from the highway. I averaged 19.5 mpg at 72mph. I was able to stay on the cruise most of the way but did encounter a little bit of traffic. I can get slightly over 20mpg but it's in the 60's and have to keep the cruise set, which is hard to do and isn't relistic driving for me.

    What I'm not impressed with is in town with most of these trucks. I notice a larger gap between highway and town with the diesels than gas engines. I get 15-15.5 in town.

    Now, I will say there are guys out there that can manage over 20mpg without much effort. My grandfather says he gets 25mpg at 65mph, but his is a '99 Ram Cummins that is a 2wd short bed. Weight makes a big difference in mileage, mainly if it's 4wd or 2wd. Thats what I've found anyway.
     
  6. chevytrucknut

    chevytrucknut Well-Known Member

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    waytogo mostly in town driving its shorter trips on 2 lane highway, i dont drive it fast so i just figgured i should get atleast 18, and 15 ton aint too much they will pull way more than that rolling weight is a lot different than just pulling a big block across the road waytogo
     
  7. RJF's Red Cummins

    RJF's Red Cummins TRC Staff Moderator

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    Well, I've had my share of "heated" discussions this week so I'll try and not get into another. one.

    Your truck probably has a GCWR (gross combined weight rating, meaning the pickup and the load behind it) of around 17-18K. The truck weighs around 6,500lbs, so that means that you can tow up to probably 5-6T behind the truck by the book. Now, I'll be the first to admit I think the factory recommendations are a little conservative and that these trucks will pull a few more ton SAFELY, but not three times the rating by the book. :poke: Not only that but the grain carts that I am thinking of don't have brakes at all.

    To sum it up....can these trucks pull 15ton behind them and then some? Yep, they sure as hell can, I pulled 79,400lbs behind me. Is it safe? NOPE! I pulled a truck that still had air in the tanks and had his own brakes, otherwise I wouldn't have done it.

    The truck may have the power to pull, but it can't stop that load. Not to mention what a few good pumps could do when that load starts swaying. THere is a reason why you can only trailer 10-14K or so by the book.
     
  8. BadDog

    BadDog TRC Staff Staff Member

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    I agree with Bobby, it's not that they can't pull it. The problem is they can not reliably control it. A load like that will push a light truck around and get you into trouble FAST. Lots of folks (mostly farmers) get away with it, but some don't. And when they dont, it gets bad. As someone who spent most of their early life on the back roads of N. AL and TN, I've seen a few serious messes caused by farmers who thought they could pull a chain of cotton trailers (and similar) with a light truck...
     
  9. RJF's Red Cummins

    RJF's Red Cummins TRC Staff Moderator

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    I disagree, there.... most of us farmers know what we are doing. :) I've witnessed mostly city folk that don't know what the heck they are doing..... :stir:
     
  10. Terrain Twister

    Terrain Twister Active Member

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    I thought you said you didn't want a heated discussion!!!!!! :D
     
  11. Brisk

    Brisk Well-Known Member

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    HAHA are you kidding??? Bobby is the king of heated discussions :stir: He knows everything...just ask him! rotfl rotfl

    Bobby...you got to stop taking everything so seriously!! waytogo

    All in good fun of course waytogo
     
  12. 02dmax

    02dmax Member

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    Baddog,why do you think that because you can't get 21MPG and over that anyone that says they can is smoking something?I constantly get 21-23MPG on the highway,17-18 combined city and highway.I don't care if you believe it or not,but there are some people that are getting more than that(hand checked every tank by the way).
     
  13. BadDog

    BadDog TRC Staff Staff Member

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    Holly cow, talk about back from the grave! ;)

    And an interesting first post too.

    I stand by my earlier statement. I know a fair few people who have been driving Duramax trucks for several years now. Some are calm souls who don’t get in a rush, some are very competitive, but none of the guys I count as reliable have ever claimed more than 21 MPG. Every single claim (in person, I don’t know you at all) of higher mileage came from guys who almost always have a “bigger than life” personal (and unverifiable) story to add regardless of the topic being discussed. I myself have made that night time (lower speed limit) run on I10 across Texas in ideal conditions with no load and cruise on a cool night, and I still didn’t get over 21. I know competitive (but reliable) guys who have gone out of their way to try to achieve the high mileage just so they can say they have, and in part so they can hold DMax mileage up against what some of the Cummins guys can (apparently) reliably produce, but they consistently reported no better than 21.

    So it’s not “just because I can’t get get 21 mpg”. It’s because nobody I know except for BS slingers and web aliases have ever even claimed to do so. Are there trucks/drivers out there that get more than 21 mpg on a DMax? Maybe, I won’t call you or anyone else a liar on that point. But have I seen any independent and reliable evidence to support it? Nope, not once...

    So, instead of going on the offensive, why not tell us what it is that makes your experience different from the vast majority? What do you do to achieve that mileage? Is it possible that your odometer is off? Have you checked it against a GPS? Any mods on your truck? Camper shell, larger/smaller tires, chips, air filter, manual or automatic? What terrain and at what altitude? Maybe there is something that does make your experience different, maybe not. I’ve seen lots of claims slung around, but I’ve never seen anyone able to back it up.
     
  14. 02dmax

    02dmax Member

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    I am a retired gentleman who is not "bigger than life" and drive the speed limit(65MPH in Wisconsin).I don't think the truck has ever been over 2000 RPM and that was one time I took it up to 70 MPH.When I take off,I slowly bring in up to 1500RPM and just let it go through the gears.As for the truck,it is a 2002 2500HD D/A reg.cab 2WD work truck.It has the stock size tires(the speedometer is not off),I don't own a GPS.I have installed a K&N cold air intake,and 4" Magna flow exhaust.Other than that,completely stock.I think this truck is capable of more,I have some other things I want to try to get it up to 25MPG!
     
  15. BadDog

    BadDog TRC Staff Staff Member

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    Well, all I can say is "Congrats!", you seem to have achieved what few others (none in my experience) have done. What you describe would surely be the way to do it, as RPMs need to stay down below 2000 to maximize mileage. If you can stand it, and want to try to push it further, then try to keep the RPMs at 1800. Assuming your engine matches the torque graphs for the stock '02 DMax, that should be the "sweet spot". The reg cab may also be contributing significantly (change in aerodynamics?) since the vast majority I know are CC.

    Good luck and welcome to TowRig!
     
  16. 02dmax

    02dmax Member

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    Thanks,my truck is also the lightist.I think the biggert difference is the 2WD.Next spring(truck stored for winter)I plan to change the gear ratio from 3:73 to 3:21.that should keep the RPM at 1700-1800 on the highway.I also want to install a milage type programer in the spring.I also read of a fuel cooler that helps mileage.
     

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