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Chevy Silverado and GMC Sierra Duramax Fuel Mileage

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  • The tip about getting the engine to run at 180 degrees made a little difference in the trucks mileage. If nothing else, the cab warmed up sooner. Bottom line, if you want better mileage, stay off the throttle. I presently have the easy tuner set at 80 e. at the engine responce is very noticible. Fun to drive. Doing more highway driving now, but the mileage still is not 20 mph. stay tuned and thanks for all your input.
  • Interesting reading...

    Our '07 2500 Classic is great but for the mileage... avg. 13 mostly hwy and between 9-11 towing a tiny little 2 horse bumper pull with 2 ponies! Grrr. It's got 55K miles and has been well maintained.

    My old '03 Duramax got 21 hwy 17 city... and towing got around 16 pulling a bigger trailer with bigger horses. I was hoping to get the same or better.

    When I did the research before I bought this truck, all said the mileage was similar to the '03... now I see these threads and wonder what's going on?

    Is anyone out there getting good mileage at all? If so, enlighten us!
  • rgferrirgferri Posts: 3
    edited March 2011
    I have a 2006 2500hd crew cab with a 3.73. i was wondering if anyone has some advice for better milage. right now im getting about 11 in the city. was driving a 2004 sierra 2500 and getting 17.5 in city. both truck are bone stock. any pointers?? thanks!!!!
  • first question: is it a diesel??? If not that is about the best you are going to get. Crew cabs weigh a lot more. If it is a diesel then I recommend you decide if you like the acceleration more than mileage. Take it easy on the diesel and you will get better mileage. If that doesn't work then the next easy step is disconnect the batteries, causing a transmission computer reset and then drive it easy. The Allison tranny behind the Duramax is a learning computer for shift points and the more hard acceleration the less up shift and fuel savings. Also the faster you drive the less fuel savings from the engine computer and tranny computer. An '06 diesel is the best one GM has produced lately for mileage.
  • rgferrirgferri Posts: 3
    thanks for the advice. Yes it is a diesel. I just purchased it used and the computer said 10mpg and after a few days of driving i brought it up to 11.1 mpg. i have only been driving it for about 3 days now. i am hoping it keeps going up from there. I guess i was expecting mileage like my fathers 2004 duramax. is it taking me longer to raise the mpg because it has been at 10mpg for so long. would re-setting the computer on the instrument panel give me a more accurate reading??? any aftermarket products you guys suggest??? the truck has 104,800 miles on it so i am not worried about the warranty.
  • Oh yeah, reset that stupid display. The DIC that you are getting your MPG stat from arrives at it's calculation from the float position in the tank and the throttle position which means your pedal position as you drive. It is horribly inaccurate and the longer you leave it the farther off it will be. Mine say 14.4 mpg right now because I haven't changed it all winter. Winter is when a diesel gets the worst mileage for a diesel engine is most efficient when the engine is hot. I do not know where you live but here in MN I not only have the "Winter Front" covers on the grill and bumper, I added cardboard from the radiator down in front of the tranny radiator plus I covered the 2 holes left open on the bumper for the tow hooks with cardboard. This winter has been really cold but my drivetrain temps have been good thanks to the block heater and all the covers. No tendency to overheat either even on the few days that have been in the upper 40's or 50. So my calculated mileage at the pump has been 17 to 19 this winter. Close to the lowest I have seen in 50,000+ miles. Spring through fall I get 20 to 22 city(with No load) and when I tow our 16,000 lbs of boat we get 13 to 15. It really matters how you handle the drivetrain. I moderately accelerate to 35 mpg then back off and let it shift to 4th and if needed keep accelerating easy to highway speed. Maximum economical speed is 65 to 67 mph depending on head wind. I can hear the engine start to work harder in 6th with the torque converter locked up somewhere around that speed. It is the complete lack of aerodynamics of the truck which is like shoving a large stack of bricks through the air. But the dash MPG estimate is always off by 3 to 5 mpg or more for me since I have a steep driveway that it has to climb. Also you do not need to idle the truck when you stop to keep it warm for it has a huge amount of fluids that stay warm quite awhile. If you need more advice feel free to let me know if you need my email addy. Oh and if you wish to "chip" your truck get a tuner that connects in the wire connectors under the hood. The ones that plug in inside are DANgerous. For mileage without a load the lower program settings add air to the engine with the higher power setting adding fuel and air. High power settings are for people who need or wish to show off the diesel power but they can easily damage a transmission. The Allison is the "weak" point in the drivetrain but it can handle as much as 15% more power if it is in good condition. To check that have the fluid changed for the external filter has a magnet in it to detect how well it is operating.
  • rgferrirgferri Posts: 3
    Thanks a lot. Great help!!! I'm not an aggressive driver by any means, i just want to get better mpg. we never reset my dads in-dash mpg display and for some reason it always ready about 17 city and 21 highway. hopefully like you said with me resetting that mpg feature it will start to show more accurate readings. as for idling the truck, i usually don't let it idle......its garage parked so it doesn't get really cold even though this winter was one of the harsher winters Ive seen. I'm from Michigan by the way....sorry if i didn't give you that bit of info...ha ha so yea we have had a cold one this year as well, maybe not as cold as you guys but close enough.

    Thanks again for all your input and info!!
  • kula_jonkula_jon Posts: 1
    Hi, I bought the H&S XRT Pro package with the cold air intake and DPF delete pipe. I just unplugged my EGR and air intake valve connections. I just switched to "hot". I have not seen the gains that you're speaking of, up to this point. I was getting 13.3 and it went to 14.4 but that's all. Am I missing something? I seem to have copied your setup (except I don't have Banks, I have S&B intake).I have a 08 2500 HD with the 6.6 LMM Duramax, extended cab, Allison trans, 4x4 LTZ. I upgraded so I could haul my backhoe. Since it's so dang slow I'm not hauling anything these days.
    I'd appreciate any pointers. Thanks.
  • My quick reply would be that if you didn't replace the computer with one that can work with the stock system you bought the wrong computer. Banks, Edge systems and another all have the purchaser install a "Y" connecter under the hood in the main wiring loop between the stock computer and the engine. They also add an EGT sensor on each manifold. The cold air intake + the bigger intercooler + the bigger exhaust w/o obstructions is how you get to run power levels higher than 2 steps above stock. The upper 3 or 4 power levels are NOT recommended for a stock transmission. Stock Allisons of that year are capable of around 750 ft-lbs without damage. I found all this out for I exceed the GCWR of my truck by about 4,000 lbs when towing our 18,000 lbs of boat & triple axle trailer with us loaded out for a vacation in the bed and cab of our '06 Duramax which still can get 14 to 15 the way I drive it under load with the first 2 power settings. At stock I get 11 to 13. My installer did not disconnect any of the stock systems, just added systems onto the stock which quails more mileage and performance. I did this because I lost so much when 500 ppm fuel became unavailable after '08. My guess is that you have actually hurt your performance and perhaps endangered the engine and transmission. good luck with that.
  • jerryeljerryel Posts: 2
    My fuel economy is 14.8 mpg empty according to the truck computer. My 02 Duramax got over 20 mpg empty and around 12 mpg pulling my travel trailer. I only have 1200 miles on the 2011 and baby the engine. I never drive over 65 and most of the time I drive 55 mph. I recently took the truck to the dealer for a diagnostic check and they couldn't find anything wrong? All the reports I have read state that this truck gets from 18 to 22 mpg on the highway empty driving at 65! Is mine just a lemon? or do I need to wait 5000 or 10,000 miles for the fuel economy to improve? My 02 Duramax had a Bully Dog chip set at "towing". It also had the 4" exhaust(no catalytic converter), an Air Raid air cleaner and the Air Raid air intake ring. I love the new 2011 Chevy Silverado but not the fuel economy....Jerry
  • hillsdale56hillsdale56 Posts: 15
    Hi, enjoy your new truck. I have an 06, the best year for fuel economy. Your truck will do better as you drive it more. By the time you get to 5000 miles should get better. The dpf kills fuel economy, you will not get the same mileage as with the 02. On my truck, I'm gutting the catalitic converter, and installing a magnaflow muffler. May get like 27 miles to the gallon then. There is no emission test on diesels,, here in ny. Stock pipe is 3.25. I think yours is 7 inches. After you break yours in, contact diesel domination in montana. Check them out on your computer.
  • barrailbarrail Posts: 27
    hi hillsdale; when you say your gutting the catalitic converter, are you just replacing it with a test pipe and do you have to reprogram the onboard computer?
  • jerryeljerryel Posts: 2
    I owned a 2001 Silverado, 3500 HD dually with the 8.1/Allison. I owned a very large camper at the time(11 1/2 footer that weighed over 5000 lbs). My mileage when I carried the camper was 8 mpg and around 11 empty(at 75 mph){we lived in Nevada at the time}. When I towed and carried the camper my mileage was around 6 mpg(at 60 mph). The truck was very powerful but the fuel consumption was expensive! I have owned a 2002 Duramax and recently bought a 2011 Duramax and find the diesel is well worth the extra dollars for reliability and much better fuel economy.
  • hillsdale56hillsdale56 Posts: 15
    What I'm going to do isremove the cat, and run with a test pipe. I'm also removing the stock muffler. Installing a magnaflow. 28 inches long, 3.5 inches in and out. When I get it set up and drive for a while, I will let you know how my milage is. I'm going to bring it back to stock. Tune
  • Hello everyone what a storm, upstate ny is a mess. Here are my results. After doing what I said I can get 26 to the gallon with a good grade fuel. I used 3.8 galllons to go 102 miles. City and highway mix use is around 6t00 miles per tank now. Filled to top of neck. Truck does not smoke at idle or while running. I'm happy with it
  • How do these modifications impact CA emissions tests at registration?
  • May I ask, what modifications were made and to what year D-max?
  • What I did was remove the cat and stock muffler. Installed magnaflow number 129909. Pipe is stock size. Truck does. Not smoke at idle or when running. Also have a tuner froom diesel domiination. Ruunniing 25 lbs of boost at 1600 rpm. Look into his tuner. Steve shellly s a good guy and kknnows what he's doing. My truck is a 06. 3.73 4wd hd.. now at 420 hp. To answer the post about california, I not familar wth your emission. Testing. Dooo they put a snffer n the tail pipe, use a mirror to look under the truck? Here n new york we don't have that.no. emiissiion testng on diesels
  • Looking for some advice here folks...
    i drive my truck about an hour each way to work daily, purchased this truck in may of 2011 and was thrilled to see it was getting 18mpg on the drive home! After having the truck a bit i put a soft tonnaue cover on it and immediatly noticed a drop in fuel mileage, to date the truck has been getting around 15.9-16.2 mpg. Wanted to improove mileage so we put cold Air intake system with K&N and did Exhaust with hypertech programmer on stage 2. mileage has not gone up at all since the updates :-(
    Any advice would be much appretiated!!!
  • barrailbarrail Posts: 27
    did you rely on the on board DIC to determine your mileage or did you divide gallons put in to miles driven actual.
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