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    Red face GMC 6.6L Duramax Diesel Questions..

    I've been doing some research on buying a used 3/4 ton diesel. I perfer the GMC with a crew cab(4 door). I would like to hear from people who own a truck with any configuration of the 6.6L Duramax engine. What fuel mileage can be expected? I understand from other forums that rear gear ratio and driving speed have the greatest impact, so I'm looking for the best mileage at around 65 mph. I pull a 19 foot bass boat every weekend from 15-100 miles one way, but would like to have decent mpg during the week. I would also like to know what problems people have had. I am looking for a 2wd model, so problems with 4wd suspensions being weak off road shouldn't affect my decision. The truck would be my personal vehicle for everyday driving. I am open to year models from 2001-2008, but right now, the 2004 seems to be the most available in my price range..

    Yeah, not much of a fire related question.. But I figured people here are the best resource I have available, thanks..
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    I own a '04 1/2 2500HD duramax/ally 4x4 that has a lift, larger tires, and a power programmer and I get 16 - 18 mpg with a combination of city/highway driving. If you're looking a 2004 model you need to decide which model Duramax you would like/are most comfortable with. In 2004 GM switched from the LB7 model Duramax to the LLY model Duramax. The LB7's generally have better mpg but are a nightmare to change injectors on. The LLY's lose a few mpg due to the epa and federal emmisions requirements. The LLY's have easier to swap injectors but some LLY's are overheaters. The best advice I can give you is to join some forums specifically for the Duramax such as dieselplace.com for all the info you could possibly want and some you don't want.

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    Last edited by jlcooke3; 07-22-2008 at 11:52 AM. Reason: left something out

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    I am thinking I would prefer the LB7. I would like to find one that is unmolested, and add my own choice of programmer to it. My understanding is that GM warranties the injectors until 200,000 on the LB7.. Most of the forums I've come across so far end up in the Powerstroke/Cummins/Duramax, mine is better than yours argument, to which point I begin to feel that the information becomes a pizzing match trying to outdo one another. I'll check out the one you suggested. Thanks..
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    The warranty is 7 years or 200K...01-02's are nearing the end of the warranty period.

    I have an 02 CrewCab Long bed Dually with an LB7. I can get >20 mpg unloaded if kept under 65 mph. It is a great truck.




    Try dieseltowingresource.com or dieselplace.com for much more comprehensive information

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    I own a 2002 2500HD Chevy Crew Cab, 4WD, short bed. I added a hypertech tuner to it a couple of years ago. The only issue I've had so far is a bad glow plug controller which was replaced under warranty after some haggling with the dealer. I get about 18 mpg to and from work (mix of city and highway). I'd probably get better milage if I could keep my foot out of the gas, and if I drove it more. Towing, I seem to get about 14 mpg no matter what I'm towing. I tow a 32ft 5th wheel and a 18' boat.

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    I own an '02 Duramax/Allison Crew cab 3500LT 4WD Dually. It has the LB7 engine. I couldn't be happier with it! I added a straight-pipe 4" exhaust, an AFE Stage II intake and the Edge Juice power programmer among many other little upgrades, both inside and out. I get about 16 mpg in town and about 19-20 hwy at 80 mph. When I pull my 8x20 enclosed trailer, the mileage drops to about 14 and 16, respectively.

    The only problem I ever had was with the crappy stock Monroe shocks (3 of them were completely blown at less than 18k miles).
    I replaced them with Bilstein shocks and they made it ride like a dream.

    It's a great engine and it still amazes me that a 7000 lb truck can smoke the tires (duals, no less) into 3rd gear!

    The absolute best site to learn about these trucks is www.thedieselplace.com.
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    I've heard that 20 mpg was possible at or near stock. A few of my friends have tried to talk me out of a Diesel, saying they will not get the mileage of a gas engine. I have one who drives a 07 Dodge 3500 with the Cummins, and he reports 16 mpg. I know that the extra weight of the dual axle assembly creates more drag. What I don't know is how he drives it (stop-sign to redline??)..

    I'm not planning a purchase in the near future, but I wanted to do some research before I made a mistake. I'm waiting to see how the 5.3L gas burners in the 1/2 tons are handling the ethanol blends..
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    Quote Originally Posted by rhvfd1214 View Post
    I've heard that 20 mpg was possible at or near stock. A few of my friends have tried to talk me out of a Diesel, saying they will not get the mileage of a gas engine. I have one who drives a 07 Dodge 3500 with the Cummins, and he reports 16 mpg. I know that the extra weight of the dual axle assembly creates more drag. What I don't know is how he drives it (stop-sign to redline??)..

    I'm not planning a purchase in the near future, but I wanted to do some research before I made a mistake. I'm waiting to see how the 5.3L gas burners in the 1/2 tons are handling the ethanol blends..
    From what I've been told by several people that own them, the 5.3 gets a few less mpg than it's diesel counterpart.

    Not sure about E-85, but I would expect it to be about the same, or slightly less than non-blended gasoline.
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    Quote Originally Posted by rhvfd1214 View Post
    I've heard that 20 mpg was possible at or near stock. A few of my friends have tried to talk me out of a Diesel, saying they will not get the mileage of a gas engine. I have one who drives a 07 Dodge 3500 with the Cummins, and he reports 16 mpg. I know that the extra weight of the dual axle assembly creates more drag. What I don't know is how he drives it (stop-sign to redline??)..

    I'm not planning a purchase in the near future, but I wanted to do some research before I made a mistake. I'm waiting to see how the 5.3L gas burners in the 1/2 tons are handling the ethanol blends..
    I have an '02 1/2-ton with the 5.3 (4x4). When I put the "super" unleaded in it, my fuel mileage drops to around 15 mpg. I typically get closer to 18 or 19. My wife's Envoy (also a 5.3 4x4) does the same thing, but drops down to 13 or 14 mpg.

    Most everyone at work that drives a diesel, whether it be a Ford, GMC, or Dodge, seems to be getting around that 18 mpg mark. If it weren't for the fact diesel is so much higher right now, I'd make my next truck one (not that I won't anyway, but that's a ways away).

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    Quote Originally Posted by fireman4949 View Post

    Not sure about E-85, but I would expect it to be about the same, or slightly less than non-blended gasoline.
    The best mileage I've seen on E-85 on the EPA's website comparison was around 11-15mpg with 15-20mpg on non-ethanol gas for Chevy's 5.3L, if I remember right. Around here everything is 10% ethanol.
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    I've looked at trucks with 70-150,000 miles, since they are in my immediate price range. What is the expected life span of this engine? Are there any ones out there running in the 200-250,000 mile range without major problems? My current 5.7L '96 Chevy is bumping over 220,000. It had 170,000 when I bought it in '04.



    Yeah, I know, go to the diesel forums... I keep reading through them, but I figure most people with complaints will use the forums as a way to vent frustration, whereas happy customers will not need to chase forums for answers. Most of the issues with injectors and lifespan are only the horror stories.. Continued repairs, rebuilds and injector replacements seem to dominate a lot of what I've read.
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    I'll try to answer some of your questions.
    What is the expected life span of this engine?
    Not sure what GM designed it for I'm expecting 500,000 miles out of mine.
    Are there any ones out there running in the 200-250,000 mile range without major problems?
    Yes there are quite a few out there with over 250,000 miles and I have seen some with over 500,000 miles.
    Yeah, I know, go to the diesel forums... I keep reading through them, but I figure most people with complaints will use the forums as a way to vent frustration, whereas happy customers will not need to chase forums for answers.
    Many go to the forums in order to get help with problems and quite a few go in order to keep up with latest mods to increase power and reliability.
    Most of the issues with injectors and lifespan are only the horror stories.. Continued repairs, rebuilds and injector replacements seem to dominate a lot of what I've read.
    The injectors were/are a major problem on the LB7 motors. Part of the problem was the cost in replacing the injectors as the valve covers had to be removed in order to access the injectors. This problem has been pretty much solved on the LLY and later motors.

    Many of the lifespan issues can be traced directly back to fuel. The key to diesel longevity is clean fuel. One major problem with the Duramax is the factory fuel filter only filter down to 6 microns. This is fairly coarse when considering the tolerances that the injectors are manufactured to meet. This problem has been solved by the addition of a Pre-OE fuel filter that utilizes a fuel filter that filters down to 2 Microns. This allows for much cleaner fuel to be used by the injectors and helps prevent injectors from sticking due to foreign material. Their are kits and DIY articles available and they run from $100 for DIY kits to $300 and up for complete bolt on kits.

    Now for some completely unscientific opinion. The ULSD that is being forced upon the diesel fuel market is, IMHO, a contributing factor to the failure of injectors in diesel engines. The ULSD does not have the level of lubricity of the older LSD. This can be fixed by adding some type of diesel additive. Anything from 2-cycle engine oil to scientificly developed diesel additive's can only help increase a diesel engine's lifespan.

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    Now for some completely unscientific opinion. The ULSD that is being forced upon the diesel fuel market is, IMHO, a contributing factor to the failure of injectors in diesel engines. The ULSD does not have the level of lubricity of the older LSD. This can be fixed by adding some type of diesel additive. Anything from 2-cycle engine oil to scientificly developed diesel additive's can only help increase a diesel engine's lifespan.
    I have a 2002 and have not had any issues with the injectors. I figure that will happen just after the extended warranty on the injectors expires. I don't have any data to prove it, but I seem to be getting worse milage after the change to ULSD.

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    You dont need any data to prove it ENG.....ULSD sucks in just about every aspect. You will get the best milage from HSD but the DOT and the government seem to frow when you burn it
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    I have an '05 Chevy 2500HD (LLY motor) 4x4, crew cab with an AirAid intake system with 48,000 miles. If I keep the cruise set 55-60 I get 22-21.3 mpg respectivly right now during the summer months which I think is pretty good. Highway speed(70mph) I get around 15.5mpg. Guys at work with 2WD 1500's get worse fuel mileage. I just finnished building an HHO fuel cell and will be installing it soon, I'll post the findings for you. I love the truck and the engine is much quiter than the Powerstroke or the Cummings.
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    [QUOTE=Firemedic 61;973583] I just finnished building an HHO fuel cell and will be installing it soon, I'll post the findings for you. [QUOTE]

    I've done some checking on the whole "HHO" scams. Be careful that you do not overload your alternator. The amount of electrical energy required to convert water to an amount of Hydrogen gas that is usable by a combustion engine is far greater than the capacity of the vehicle's charging system. Most cases will result in a loss of fuel economy as the alternator is trying to charge the cell, thus creating more drag on the engine. Mythbusters tv show's web site had several articles in their viewer forums about the great "HHO" theories. I fell for some of the advertisement, but researched it before trying it, and decided it was just a scam. Something didn't sound right when I tried to see what the amp draw on the alternator would be.

    If you don't like the ULSD fuels, look for those that are blended with up to 10% biodiesel. It will have a greater lubricity, but I still reccommend a quality additive, preferably "Howes" brand. I've used it for years in commercial diesel trucks.
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    [QUOTE=rhvfd1214;974705][QUOTE=Firemedic 61;973583] I just finnished building an HHO fuel cell and will be installing it soon, I'll post the findings for you.

    I've done some checking on the whole "HHO" scams. Be careful that you do not overload your alternator. The amount of electrical energy required to convert water to an amount of Hydrogen gas that is usable by a combustion engine is far greater than the capacity of the vehicle's charging system. Most cases will result in a loss of fuel economy as the alternator is trying to charge the cell, thus creating more drag on the engine. Mythbusters tv show's web site had several articles in their viewer forums about the great "HHO" theories. I fell for some of the advertisement, but researched it before trying it, and decided it was just a scam. Something didn't sound right when I tried to see what the amp draw on the alternator would be.

    If you don't like the ULSD fuels, look for those that are blended with up to 10% biodiesel. It will have a greater lubricity, but I still reccommend a quality additive, preferably "Howes" brand. I've used it for years in commercial diesel trucks.

    Just though you might like to see this, there are guys on fullsizechevy.com that are running hydrogen systems right now and are seeing gains in mpg. If you can read past some of the nonsense thorugh out the thread you can see that this system works. These guys have come to a conclusion that the hydrogen acts as a catalyst to help fuel create a more complete burn.
    http://www.fullsizechevy.com/forums/...rformance.html

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    I have an 04.5 Chevy LLY with the Predator programmer and 4in turbo back exhaust and 285/75/16s on it. I can get about 15 to 16 around town. Do some reading on EFI Live. There are guys that are running tunes that they have built that are getting 20mpg in the city with this program. That is something I am saving for but first I want to build my transmission up.


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    Up this way, Diesel is running 60 Cents per Gallon more than 87 Unleaded Gas, and can be as much as 75 Cents more, in some places. (Currently $3.69/$4.29-$4.45) Dealers seem to be both downlisting the price and/or wholesaleing Diesels South and West to areas where they are more in Demand. I'm not doing the math, but for that price difference, the MPG for a Diesel would have to be Noticeably Higher than a comparable Gas Engine to make Economic sense.

    I'm running a Ford F150, pulling a 2 axle Trailer when I'm going to Tractor Pulls. The Tractor and stuff on the trailer add about 3K to the "Unhitched" weight that the Truck normally runs with. 4X4, Auto, Air, etc. and I still get 15-17 MPG on 87 unleaded, sometimes a mix of 10% Ethanol in 87 unleaded. And it's a quiet ride.
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    My basis for wanting a Diesel are mostly because I don't like the Ethanol gas blends. As far as fuel mileage, I was happy with my 16-18mpg of my 5.7L in my 96 chevy. However, with the ethanol blend that is now mandatory, I've been getting 14 mpg. So, if I decide to get a new vehicle, I would prefer to go diesel. If I can get 20 mpg, then that would be a 6mpg better average. At 10 gallons, with my current truck, I get 140 miles for roughly $37. (at $3.70/gallon) At 10 gallons of diesel ($46~$4.59/gallon), I might get 200 miles. For roughly $9 more, I get 60 more miles. At 14mpg, it would cost me about 4 more gallons to go that extra 60 miles. 4 x $3.77= $15.08 more to stay with my current gas burner.

    Put my boat behind my truck and it drops to 11-12 mpg, sometimes less depending on where I'm fishing. I wonder what the mpg would be pulling that 19ft Triton with a Duramax..
    I fish for a living, but I have to work for money...

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