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Chevy Silverado and GMC Sierra Duramax Fuel Mileage



  • I just purchased an 06 gmc 2500hd duramax extended cab truck with 30000 miles on it. I cant seem to get the mpgs over 13.8 unloaded. It has 285s and it has plenty of power. I haven't took any long trips in it yet. The longest trip Ive been in it is about 50 miles in it both ways and it id hit 14 by the time I got back. The mpgs stay right around 13.8. Is this normal for this truck or is something wrong?
  • #1.Do NOT trust the computer for mileage. The short drives you have taken the truck on will leave it as much as 5 mpg low. Also you need to know how to reset the computer. Reset it before going on a 150 to 200+mile cruise at 55-60mph and then refill the tank and calculate your mileage.
    #2.285/75 tires on any wheel bigger than 18" are too big for this trucks gearing if you have the 3.73 final drive. They have a much wider and longer footprint than the stock 245/75 16" wheels and tires. Also the computer than runs the dash MUST be programmed for 285 tires so as to tell you the actual miles you have driven. This size tires will reduce the miles driven if it has NOT be calibrated. Any Chevy dealer with a diesel shop can do the calibration. If the truck has the 4.11 final drive you will be lucky to get 20 mpg. With the 3.73 at 55-60mph you can get 23-24mpg with ULS fuel. 2 mpg better with LS (500ppm sulfur)diesel. All these are unloaded. 285/75 16s are nice in winter but not summer driveing when you want good mileage. If you like the "Big" tire look I can reccomend some 245/75 16s that look Awesome and once someone reads the brand you will get a LOT of respect. But they can be expensive if you do not shop carefully.
    #3. The fuel you use makes a big difference. ULS, Ultra Low Sulfur diesel(15ppm sulfur) reduces your mile by at least 2 mpg and more in winter or if you love to use your right foot a lot. A lot of truck stops still have 500ppm Low Sulfur(LS) diesel and it IS marked on the pump plus it costs less. Also depends on your state you live in. There are "Cetane" additives(cetane is the measure of power in fuel, octane is the measure of the resistance to explosion) which will help mileage and power but most are just too damn expensive.
    #4. Better mileage is achieved with this engine and tranny(which learns how You want to drive) by taking it easy while crusing but accelerating through the first 3-4 gears, up to about 35-40mph quickly so that you can get it into 5th gear and get the torque converter to lock. At 52-53mph the tranny goes to 6th gear. Driving this blocky, blunt, lumpy truck at over 60 mph drops mileage due to wind resistance. This can be offset by using 265/75 16s with no more than a 9" treadwidth and changing the final drive(differentails) to 3.42 ratio. You can then get up to around 70mph with about the same mileage as stock at 60mph. Driving this heavy beast at more than 75-80mph is Dangerous since it is not designed to be a sports car. It is a Great Tow vehicle for toys though.
  • rohrich, i am a heavy truck driver, mostly 5 ton long distance with high value loads. I have driven over 2 million miles on commercial cars and trucks on LPG, CNG diesel and bio-diesel. I like the propane ones the best.
    Of all the guys who have used a propane boost system on the big rigs, they are happy. When i say big, i mean 80,000 pounds gross weight. One was a 375HP Detroit diesel with a 13 speed overdrive and the other was a 400HP also with an 13 over. The 400 HP truck had been using the Bullydog propane boost system for 1 1/2 years and increased his mileage 38 percent for long distance trips. The other truck did the same route for 4 years with the exact same weight on the truck hauling from Indianapolis to New Hampshire 3 times a week. He had been using the same propane boost system and he got 32 percent fuel improvement. Well worth the cost. The propane would be sucked into the turbocharger when it kicked in, about 800 to 900 RPM. At idle, no propane would enter the system.
    Federal law prevents them from having a LPG tank bigger than 150 gallons or else their insurance rating would change.
    Set up a national fuel discount card for LPG with a major or set up a prepaid card at one of the truck stop chains which all sell propane. You can save a significant amount of money on the west coast if you get the national propane credit card from the biggest American producer. You will not get as serious a discount from your state distributor unless you mary his ugliest daughter ( or take his ugly wife off his hands )
    Always run 100 percent synthetic oil in the engine to improve fuel mileage. Use 20W50 or 15w50 or in the coldest weather use 15w40 100% synthetic diesel grade engine oil. Change your air filter when it starts to turn slightly grey. Do not let the truck idle except when it is minus 15 degrees. Always use a block heater overnight below 35 degrees. This way, you just jump in the truck in the morning and go saving time and fuel. Slow down to a more reasonable speed. You can save 20 % on fuel costs just by slowing down 10 MPH from 75 MPH to 65.
    Draft the big rigs when going up hill. It also works great giving an extra 5 MPH on level ground if fully loaded or on a windy day. If your trucks nose was parked out of the direct wind, inside a tarp, then it would be much easier to start even with a block and battery heater. You can buy an electric magnetic oil pan heater that sticks to the bottom of the pan and keep the oil warm all night. Electricity is cheap so buy one for the automatic transmission as well. Use the same fuel additive in the winter that the big rigs use. It will aid the starting and smoking when very cold at startup. It will help the MPG and power by about 4 percent as well. All truck stops sell it.
    All the above will save you 30% on fuel if driving 20 miles or less. Buy a lottery ticket
  • openend22openend22 Posts: 12
    yes there is something wrong with it.. between the overheating and the steering its not safe to drive..
  • iamsziamiamsziam Posts: 1
    I have an '06 Duramax. I changed to Amsoil 3000 HDD 5-30 @ about 11,000.
    It has been like a breath of fresh air. I followed up with a call to Amsoil and spoke with a "lubrication expert" who convinced me that their product was superior. I"d say don't wait to change it.
    I'm ready to buy a chip if it can pay for itself.
  • hd82hd82 Posts: 13
    I drive a '07 F-250 Crew cab LWB with Turbo Diesel. I was told the interval for oil changes is 5,000 miles, this can get expensive when driving 1,000 miles a week. I spoke to another F-250 owner who told me he uses "Purple Oil" and doubles the mileage between changes, (10,000 miles). My questions are; What is Purple Oil? Is it true I can change less often? Do I need a longer life filter? Will this harm the motor? Will the cost of one Purple Oil change be about the same as two regular changes?
  • The oil is named "Royal Purple" and the diesel product is 15-40w. It is going to give me at least 12,000 in my Duramax. It was changed in July 07 and if it has not gotten to needing changed by 1 year I will do it anyway. IF you have the 6.0L ford diesel I would not push it much beyond 8,000 miles even with Royal Purple. That engine is notorious for failures so I would want to do everything I could to prevent it. My Duramax holds nearly 3 gallons of oil with filter change and I would hope that the Ford is close to that amount. Royal Purple makes all types of lubricants and can make a big difference in mileage and service needs. GM uses it in their differentials and in the Allison tranny. Maybe part of the reason my '06 came with a 100,000 mile drive train warranty.
  • I have owned my 2004.5 LLY Duramax 4x4 Shortbox with Allison since new. The average mpg always showed 16.9 from the day I got it until I recently had the instrument cluster replaced, now it shows 12.9 mpg. Never varies.

    Add the fact that the exhaust fumes are deadly and often get into the cab, especially when just stopping in traffic, sometimes when driving in town too. When you shut off and get out, you can smell it really bad but not always.. Also, there is sometimes a rough idle when one pulls up at a junction. Plenty of power, etc new K&N air filter system.

    Could this problem simply be a too rich fuel supply making it smell and have bad mpg? Could a cat problem cause this?

    I don't know when the smell started as the wife "stole" my truck for her work from the day we bought it and only recently gave it back when she got a new Jeep Liberty. When I asked her about the smell she said, "Oh didn't I mention that? It's being doing that for a long time".

    Thanks for any advice you can offer.

  • a friend tells me he puts two quarts of marvel oil every time he fills up.
    is this good or bad for this truck, I am interested in buying his truck
  • tdiddyotdiddyo Posts: 1
    I just bought a brand new 08 Silverado 2500HD with the 6.6L Duramax w/Allison and am wondering what I can do to increase my mileage while towing my 5th wheel trailer that weighs about 13,500 - 14,000 Lbs with gear and a little water. It looks like I'm currently getting about 11MPG which I know is really good compared to gas engines. Is there anything I can do to improve the mileage even more?
  • gdrogersgdrogers Posts: 1
    You are so right, 55-60 MPH seems to be the optimum speed range. Over 60 up to 67+/- brings it down 5 MPG. Over 70 and up and you can watch the fuel gauge go down!!!
    You peaked my curiosity. What tires are you recommending to achieve the "Big" tire look? My '03 Duramax with 3:73 ratio behaves exactly as you have stated. The stock tires gave me 40K+ miles easily, only changed them out then because the dealer blew one out in the shop. Now at 83K the second set will soon be due for replacement. I like the bigger tire look and like to drive 65 to 70 MPH.
    A great towing machine it is I just wish I could do better than the 10-11MPG. I get that full (8-10K lbs) or empty (2K lbs) when towing, it doesn't seem to matter. Any and all suggestions are appreciated.
  • dddtdddt Posts: 13
    Peter I have a 06 Duramax 4x4 crew cab, I have had it since new. I just changed my transmission fluid, Havoline, changed my fuel filter, cleaned my K & N Air Filter and I use Diesel Kleen a liquid you put in your tank to help clean the injectors and reduce the stink and black smoke out of the exhaust, works like a charm. Well in doing all of these I got 23.3 mpg on the highway with a 20 mile an hour wind coming sideways. I traveled a total of 200 miles and could not believe the significant improvement on mileage. Prior to me doing all of this I was getting about 16.5-17.5 on the highway. The vehicle runs a hell of a lot smoother and the temp on the tranny stays at about150-160 degrees. My vehicle has about 37,000 miles so really it hasn't broken in yet.

    So before you go and buy the chips and new exhaust systems that will cost you in the thousands, start with the basics and remember that your diesel is your baby; treat it like one. Pamper it and treat it nice now so it will return the favor later.

    Hope this works for you and anyone else who is having bad fuel mileage and the stink out of the exhaust.

  • dddtdddt Posts: 13
    A couple of things you can do to increase your mileage is switch your air filter to the K & N brand. This will show your best increase. Put Diesel Kleen, buy it at Walmart, into your tank religously. You will see the black smoke and stink decrease and mileage go up maybe .5 to 1.5 per gallon more. I'm not sure if those engines come with synthetic oil or not but if they don't switch to them, Mobil One, Rotella or whatever works for you. Change your transmission oil every 10,000 miles which will keep your transmission temperature low. Mine is about 150-160 while towing in 100 degree weather. Lower the temp + less stress on the engine = better mileage.

    I don't know how many miles you have on your engine, but with my truck an 06 I have 37000 and it is not even broken in yet, but that is only going to come with time. More miles you put on it the better the mileage will be. Now empty I am getting about 21- 23. Towing about 12.5-14. All depends on the conditions and terrain.
  • 06duramax06duramax Posts: 2
    i bought my 06 duamax used with 30000 miles on it. the truck has striaght pipe all the way. It has no cat and no muffler. Is this good or bad for the engine? Does it need a muffler?
  • My '07 GMC Duramax w/ 15k miles gets a dismal 13.7 mpg max. It doesn't seem to matter if I am driving in town or on the highway. If I'm towing my 2 horse BP trailer, it goes down to 11 mpg. Poor MPG while towing doesn't concern me as much as the absolutely awful fuel mileage on average. My [now probably in Mexico because it was stolen] '03 F-250 got 18-22, so this was a bit of a shock. I waited not-so-patiently for the engine to get a few thousand miles on it, thinking the mpg would improve, but it hasn't. With diesel prices at this hour $4.68/gal. here in the SW part of NM, I would like any input on how to improve my MPG without voiding my warranty. I've read on here about something called K & N air filters and a product called Diesel Kleen. Any advice/comments about these? Can the dealer put on the new K & N if I wanted it? I live in a very small town with very limited resources for any work done on the truck. [Think WalMart only.]

    Also, I put Michelin LTX M/S 265/75R16 tires on it because the tires that came with it were wimpy street tires and couldn't navigate the mud and snow here. Is there any way to tell if the tire shop recalibrated the computer? If not, can the dealer do this? Oh yeah, I'm a woman if that matters, so please respond in language that I can understand. LOL.
  • jtocjtoc Posts: 2
    I found this forum a few days ago and have read a lot of good information and tips. There are several messages where folks are saying their 06 2500HD or earlier duramax (after break in) are getting 20-24 mpg highway. Can anyone tell me how the new 08's compare on mpg? I've heard with the new emissions that went on in 07 that the mpg's took a hit. Did they? If so, how much? The couple folks I've talked with, that are complaining about the poor mpg, drive with a heavy foot so I don't know if this is true or if it's their driving style.

    I've been saving for a while waiting to move up to a 2500HD duramax. Are the new 08's good or should I be looking for a used? Thanks,

  • agman57agman57 Posts: 1
    Hi JT, If I were you, I would look for a used truck, I am running a 06 and the mileage is OK. (around 10 pulling a trailer in the wind at 65 mph. and 18.5-21 just driving around on the highway. My truck has 47,000 miles on it and the dash says it has averaged 16.8 over all those miles, pulling trailers, town driving and highway. I have 2 friends that have the new emissions trucks and they are in the 8.5-13.5 range , just driving around empty.They are sick over the mileage, because they new what their older trucks got. You will love the Duramax, this is my second and I would not want anything else. But find a pre-emissions truck. Dan
  • jtocjtoc Posts: 2
    Hi Dan,
    Thanks for the info. 8.5-13.5 is the range I've been hearing which is really unacceptable considering what is was. What are these companies thinking?

  • I have a 07 with a work tuck bed, and im stock and getting 11 mpg in town and 13 on the highway. It's 4x4 also. I really would like to get better mileage ! Would a programmer help or hurt
  • What is the my best op for this truck ? Is a programmer good or bad, will it void the warranty?. It also has a work truck bed on it, I was going to remove the rack for better mileage since we dont use it for pipe.
  • madbrit427madbrit427 Posts: 11
    They say on those TV truck shows that the Painless reprogramming unit does not leave a footprint on the ECM like some units do. So the dealer will not know you have been playing, just make sure you remove it before the tow truck comes....... LOL.
  • jimhemijimhemi Posts: 223
    You're fine. Diesels don't need back pressure as do the gasser engines.
    My 06 Liberty CRD is a straight pipe and the faster spooling of the turbo is very noticeable. The louder sound turns heads for the little 4 cylinder sounds like a V8 at WOT.
  • captbillycaptbilly Posts: 2
    I have an '06 crew cab with the Duramax. I have 315 70 R17 tires and a 3 inch body lift. I get 15.4 mpg on country roads at about 55mph.
    I think that the lift and larger tires are what is killing the mpg. I've heard that better mpg can be attained through air filters, larger exhaust, and with the superchip computers.
    I haven't tried any yet but am considering it.

    Good luck
  • tcsanertcsaner Posts: 1
    Get hold of your local Lubrication Engineers rep to purchase BTU+ Diesel Fuel Improver. You'll get upwards of 20% fuel efficiency increase. Go to for more information. This stuff really works.
  • andyc8401andyc8401 Posts: 2
    i have 2008 duramax the mileage is terrible 6 pulling 8000lbs you need to find a used one the new ones dump raw into the exhaust to burn out a filter they suck fuel and fill the cab with ex. smoke gmtold told me this normal live with it they wont even look at
  • andyc8401andyc8401 Posts: 2
    i have a 2008 duramax the mileage is terrible about 6 towing 8000lb, this thing pours raw fuel into the exhaust "to clean the exhaust filter" when it doaes this it fills the cab with smoke. i contacted gm they said this NORMAL and i should learn to live with it the y wont even look at the truck
  • losman54losman54 Posts: 22
    I have a 2002 duramax, I have it beefed up with Banks six gun tuner, K & N filter, Banks’ monster exhaust and I threw in an exhaust brake because I pull a horse 4 horse slant and 14-15K 5th wheel. Ariund town I get 17.5-18 MPG and last time I pulled my 5th wheel form Fl to NJ ...I got approx 11 MPG. I can live with that since my old Monaco motor home got about the same whe I towed my 2002 Silverado behind it on all 4 wheels. PS I have about 125K on it and it runs like a top!

    I'm about to get a new 2008-09 dully but I'm concern about the mileage that those of you who have the 08's are getting. Are the differences between these two engines that different? Or should I stay with the truck I have? I thought the MPG on the F450 sucked, what the heck is GM doing here. Have they ruined the best truck on the market?
  • losman54losman54 Posts: 22
    I have had very good luck with K&N filters. I waited unitl my 2002 reached 100K before I did anything to the engine with Banks stuff, but you can improve mileage by making the truck run cooler. The Filter will help, you can change the exhaust ...change the pipe dimension form 3 to 4", and you can even change the radiator all without avoiding the warranty (but check...just don't take my word for it). Try the air filter first and see how that helps.
  • whatswhats Posts: 1
    Can anyone confirm a bulletin on the injectors for a 2003 GMC Duramax being replaced on warranty?

    David Watts
  • kao1986kao1986 Posts: 2
    Yes the injectors are warrantied to 200,000 I believe. I had mine replaced last fall.
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