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Chevy Silverado and GMC Sierra Duramax Fuel Mileage



  • stonegstoneg Posts: 47
    I have read that dealerships are charging around $100 to recalibrate for larger tires sizes. My local dealership did not charge me a penny. Some of the performance programmers claim to be able to recalibrate, but none that I have researched will do the LLY motor (LLY= 8th VIN # digit is a 2) for some reason. I went the 285/75/16 load range "D" in the BF Goodrich All Terrain TA ko with the raised white letter out (my truck is white) so it looks good to me. I had to due some very minor trimming to the front valence to keep from rubbing, but I probably could have gone 295 or 305 after the trim. I have had a leveling kit installed prior to the new tires (raised the front up 2 1/2 inches to bring it to same height as the back).
    I saw an 05 F250 Diesel King Ranch with the same kind of tires as mine on 22" at the Ford Dealership here in Tallahassee, FL (It did look awesome) You can always put larger tires/rims on the F250 than the 2500 due to the wheel wells being more rounded than squared as the GMC/Chevy's are.
  • roughneckroughneck Posts: 21

    I am sure there must a tire out there that size that is a blackwall only. The load range might be a different story. If you don't put a heavy load on the D range will work. All the tires I saw had the D range in the 285's at the tire shop. But if your like me you might not find a tread pattern that you like and blackwall. I have a 04 chevy duramax crew cab long bed and just put 285's on it. Cooper STT(white outlined). They have a pretty aggressive tread pattern, a little noisy. I had to lift the torsion bars 1", front end alignment, shaved a hair off the front valance and some cutting of the driver side inner fender well. I still have a little rub on the back of the fender well. The only reason that still rubs is the parking brake cable makes the fender well stick out just enough to rub at full crank of the wheel. I'm real happy with how the truck looks now. I had the pizza cutters before too. But a word of advise that all tire shops might not tell you. The stock 6.5" wide rims are not recommended. It can cause uneven tire wear and all other kinds of problems. You should get at least an 8" rim or so. They'll mount up on you stock rims but I wouldn't do it. Your just asking for problems down the road. Also I haven't recalibrated my speedo yet I'm going to get a programmer for that I still have the LB7 motor plus get some more power, I can already tell the difference in fuel mileage already. I would have to guess I'm getting about 16mpg. Before I was getting around 19mpg. A guy at work put 305's on his 02 duramax and had to do some more trimming on the valence and just a hair on the bumper along with what I did, and it looks real good too.
  • pescadorpescador Posts: 7

    I would be interested in the programmer you mentioned as well. Mine is a 2004 Duramax LLY engine.

  • 05duramax05duramax Posts: 10
    Thanks to you and the others for advice on this. Most appreciated.

  • stonegstoneg Posts: 47
    Alright fella's, here's the update.
    My 05 DM has 1,100 miles on it now.
    With every tankfull my mileage gets better.
    The last tankfull average was 11.8 mpg
    I was getting as high as 17.5 mpg highway @60 mph
    and now 13.5 in the city
  • Here is what I have discovered: My 05 DM has about 3500 miles and I was only getting approx 14 mph average (highway & town)...I have found that if I keep the engine between 1800-2200 rpm, I can get from 16-18+ mpg...if I stick my foot in it at stoplights, it drinks diesel in gulps...above 2200 rpm (~75mph) I begin to lose economy quickly...on a long trip, if I keep it at ~60-65 mph (1800-1900 rpm) I can get 17-18 mpg.
  • aarongdaarongd Posts: 8
    yes, i have raised my front end to level the back. they replace the original torsion bar stops. i got an extra 3 1/4 in in the front making the front and back exactly the same height. the only problem is that you have to get a new alignment after, and the ride stiffens up a little. other than that, i love the kit. you can buy them for around $75-100. i bought mine on ebay. it takes approx 1 hr to install. and to reference your economy, i believe the 2003 duramax was the older style. mine is the lly . the older ones seem to get significantly better economy. Aarongd
  • 06lly06lly Posts: 21
    I am getting 24 to 25 MPG with my 06 2500HD, 6 speed with LLY at a steady 50 mph. (1300 rpm). Amazing that you can drive something that big and get decent milage too.
  • I have a 2005 Silverado 2500 HD 4x4 6.6 Diesel and I purchased it to help save on my towing gas. However I am only getting 6-10 MPG while towing at 65-75 MPH. I tow a Tag hitch 30' enclosed race car trailer triple axle approx 12,000 lbs. loaded, but rated for 15,600 lbs. Can anyone tell me why I am getting such horrible fuel mileage? and please explain to me what "break in" means for a diesel. Thanks!
  • 06lly06lly Posts: 21
    Well, 4X4 is part of it. More parts, more friction. If the vehicle is new, it will take 3000-4000 miles to get it loosened up a little.

    The issue with towing is frontal area more so than weight, especially at those speeds. The horsepower it takes to overcome the drag varies as the cube of mph, so slowing down a little will save a lot. Drag varies linearly with the frontal area and the drag co-efficient so those are two important factors also.
  • jbhkajbhka Posts: 1
    I just purchased a '05 4x4 crew cab GMC duramax. Previously had same truck('03) but gas. I want to maximize/improve fuel mileage. I've seen AMSOIL lubricants mentioned to improve mileage. What applications work best?
  • stonegstoneg Posts: 47
    I leveled my 05 Crew Cab D-Max 4x4 by replacing my torsion bar keys as well, and have experienced the same rough ride, expecially when going over a speed bump. It feels as if the front shocks are "topping out" when they are fully extended. Someone said I should replace the stock shocks with a longer Blistien shock. Any ideas? Also, did you notice your mpg go down after you leveled? I am trying to figure out how all these people here are getting such great economy, when I average about 11.5 in the city, 13.5 hwy, and 7.5 pulling a heavy load.
    It is from the front end not slicing into the wind by being up an additional 2.5 inches, or the 285/75/16 tires?
  • I have a 2004 duramax, lly. I was getting 13.5 mpg new, 2 months later dropped to 9-10 mpg.
    truck quit 3 times in colorado, pulling under 10000 lbs. found bad injector module after 3 trips to dealer.
    $1000 bill for gm. Same thing happening again. Starts combustion knock, severe, quits but restarts. Contacted GM 8 times to help, customer no service helpful not.
  • I Have an 05 2500HD that has had the Edge juice with attitude in it since day two. I'm seeing a big rang in fuel economy. The best I have found with stock tires is running on stage 2 at about 62 MPH. If I hold it there I'll get about 19-20 MPH depending on road terrain. I average better milage with it off if I'm driving around town, about 15-16 MPG. If I dial the Edge juice up to stage 3 and Accelerate hard and drive 75-80 I see about 13 MPG average. My experience has been that no matter what you do slowing down give me the best result. But on stage 5 she goes like a bat out hell!! for about a mile and then the EGT's are pretty high! Stage 4 is fun to drive but run too hot for extended driving over 60 MPH or loaded. In the big picture if your looking for economy buy an economy car. A diesel Truck is meant to pull what nothing else can. I
  • I have a 04 with the LLY. Has anyone had a problem with the Cold High Idle not working? If I do the pedal pattern in the manual the computer does not recognize me doing anything(I have a plain jane truck with out the steering wheel controls). With the edge and magna flow exhaust I am getting 18 to 19 MPG if I keep the settings on economy and the tach below 2100 or so. When that turbo spools up bye-bye economy.
  • Rogue,
    Have you replaced the stock exhaust or the air intake? I have been told by a diesel specialist to wait until I had between 5-10k on mine before I did the Edge or the Banks (I'm torn between them), but did say that when I do it, be sure to get a bigger exhaust (4").
    I was told by an equal number of people that the cold air intake wouldn't show much of a difference over the K&N filter in the standard air box. So I just added the filter, and I might be getting about 1 mpg better.
  • I have a 2005 GMC Sierra, 2500HD crew cab, 4x4 w/ D/max and the mighty Allison trans.. I've owned a new duramax every year since '01. I've loved them all. Even through all the injector problems. I've always gotten 15-20 mpg no matter what I pulled or how I drove. I now get 11 mpg and I try to keep my foot out of it. I've been looking at the new Preditor chip for better economy and power. I see about $500 and it plugs before the turbo and before computor.
    Anyone have experience with it?
  • Oh, I forgot. I put Michlin 285x75x16s on it and the rub in the standard left front wheel well was there. I Jacked the torsion bars a hair as I've done with all my Duramaxes. It works.
    On this rig I also put removed the muffler and installed a split, dual exhaust w/5" chrome tubes.
  • benrbenr Posts: 2
    That is Very Low mileage. I have 2003 2500HD Duramax with the 5 speed automatic and tow a Potomac 35 foot 13,400 lb 5th wheel. My wife and I take several trips a year to the mountains and traveling down Rt 81 through Virginia with the cruise control set at 70-72 mph (you have to in Virginia or the big rigs will blow you off the road); I consistently get 15 mpg on the flat country and 12-14 in the Hills.
    Do you have the Alison 5 speed Automatic Transmission?
    Are you using the cruise control? If not you could be a gas peddle thumper!
    Are you using the tow button? The only time I use the two button is when coming down out of the hills to reduce using my breaks - if you always use the tow button it will take 5th gear out of play - that would account for you lousy mileage.

    Lastly if all else fails use your warrantee and get GM to check it out.
  • benrbenr Posts: 2
    Forgot to mention my 03 is a crew cab short box.

    and what is all this about injector problems? when does this happen? I'm headed to this hills this afternoon and will roll over 30K miles this trip please don't tell me I have something bad to look forward too. Also when not towing my milage holds 18-21MPG to and from work and around town in the meto area of DC.

    also a news flash that I just came accros this morning - here I'll paste it:
    New August 25th: GM has announced a voluntary customer satisfaction program (#05546) for current owners of Duramax diesel equipped vehicles. In a letter dated August 2005, current registered owners were informed that they are eligible for one free fuel filter replacement, and GM has instructed their dealer network to perform this service free of charge through September 30, 2006. Please contact your local dealer to learn more about this free offer, or call 1-888-996-9463 if you need more information.

    Think I'll take advantage of this one, I'll need an oil change when I get back anyway.
  • I am getting a set of 285/75/16's put on this Friday. What do I need to do to dial up the Torsion bar? Also I am told I will need to get the dealer to calibrate the speedo. Is this correct?

    I would love any help I can get here. I just don't like the look of the 245's. Also was always getting stuck in the back yard if it rained. Figured that the wider tire may make the truck "float" a little better in the mud.

    Any help is appreciated.

  • victorycruiser

    When I put on the 285's I found my speedo was off about 5 mph. I went to the dealer to recalibrate my speedometer and the dealership told me that Chevy will not recalibrate the speedo on duramax trucks. Stupid huh? But I seen a recalibration chip by superlift for about $190. In case your tire shop doesn't tell you you need to get an alignment after raising the torsion bars.
  • The 285s will definitly fill the wheel wells better and make the truck look better. Everytime I've put 285s on one of my duramaxes, the right front will rub. If ya put splash gaurds on it's worse. By raising the front end with torsion bars is easy to do by reputable alighnment shop and a slight alighnment is needed. It will also rais the front end, leveling the truck.
    As for the speedometer: A difference of 2-3 mph faster than it shows. Not a big deal for me and I've never worried about it or inquired about an adjustment.
  • Is the LLY the new Duramax that is coming out with the 06 trucks? I am thinking of waiting for the new engine but it is not widely available.
  • Is anyone driving the NEW 2006 Duramax diesel yet? I'm thinking of ordering one with the new engine and am curious regarding fuel mileage in the 2500 truck.
  • KCRamKCRam Mt. Arlington NJPosts: 3,516
    According to GM's press release, the new higher-output (360/650) Dmax won't be available before November.

    kcram - Pickups Host
  • My son works for the other guy (Ford) as a mechanic on their diesel engines. They have had a lot of trouble with their variable turbos, and guess what, GM is going to use the exact same turbo (from the same manufacture) in 06' from what I have been told. Anyone else heard about this?
  • Not true. After installing BF Goodrich ko's 285.75.16, I took my '05 2500HD to the dealership who reclaibrated my speedo (at no charge). Before I put the tires on, I had a leveling kit put on (changed out the torsion bar keys). This lifted the front 2.5 inches to be the same height as the back ($275 installed). Friday I had the front shocks replaced with Blistien 5100 shocks ($250 installed). After doing the leveling kit, the shocks were extended to far, and gave a rougher ride. The new shocks make a washed out dirt road feel like a highway! Didn't turn the torsion bars at all. I did have to trim a little of the front valence to keep from rubbing though. Go with the BF' wont get stuck.
  • Under the current GM pricing I could not find anyone that would sell a DMAX with the LBZ engine. I couldn't give up the 9 or 10k off MSRP for an engine upgrade. Has anyone had experience with the 6 speed Allision Auto?
  • i have read that replacing with the stock shocks with the blistien shocks is suppose to make it better. i personally have not done it. as far as fuel economy goes,it did'nt seem to make any difference before or after the lift . i have 265/75/16 tires.i get just about the exact same milage you are stating. i don't know how they are getting the milage they say they are. i've tried driving a constant 60 m.p.h and i might get an extra .5-1.0 mpg more. .one thing that i did try and is pretty inexpensive and seems to work the best is using acetone in my fuel. approx 2 ozs per 10 gallons of fuel. it seemed to bring it up around 2 m.p.g. go to yahoo search and type in acetone diesel. click the first item. big article on using acetone. try it and let me know what you think? Aarongd
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