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Chevy Silverado and GMC Sierra Duramax Fuel Mileage



  • I think you are going to be upset because I have a 2007 3500 dually with 373 gears in rear end it got 12.5 to 13.5 towing a 46 ft. gooseneck with living quarters and a race car which weighed about 16000 lbs that was new when it was at that and the older and more miles I put on it it got a lot worse I pulled a 2200 lb boat at 75 mpg from fla to sc last week and got 10.4 mpg so any body tells you they have to get broke in is blowing smoke because mine has 99689 miles on it and shows no codes or evidence of any thing being wrong I wish somebody had an answer because gm sure as hell don't and does not really care I bought this truck and it was supposed to be the best thing on the market but I surely have a different opinion about that and it seams nobody else has an answer either good luck
  • I have the same story with my 06Chevy 2500 diesel. Slow down , IT really does improve mileage.
  • The toneau cover actually reduced your gas mileage. Myth busters on the discovery channel actually showed how a mini vortex make circles in the open bed of a truck with the tail gate UP actually has better aerodynamics than either a tailgate left down or a cover. Look it up.
  • You are correct. All one has to do is watch those covers as they go down a highway alongside your truck, always having ripples and bulges in it and it gets worse as you go faster. I think in that Myth busters the only thing they found that increased mileage on a bed was a full topper but it had to be the correct shape, I think made out of fiberglass. The metal ones don't help. My hard fiberglass deck lid which is not high enough to reduce drag actually lowered my mileage by around 1.5-2mpg.
  • My K3500 01 Duramax never got better than 15.9 mpg--and this only twice on cool freeway trips until I started using OptiMax XPD or whatever it is called. I saw an immediate jump in fuel economy to 17.65 mpg on my first tank. My guess is part of what happened is the fuel has less lubricity at the pump now. Supposedly, this will change as more biodiesel is blended. Biodiesel is great stuff but not as dense as diesel so fuel economy may not improve as these fuel blends change in the future. For now, I'd try a fuel conditioner/cetane booster. What I noticed with the Opti-whatever treatment is my engine was not working as hard. I needed a tiny bit less throttle to hold a given speed and it ran quieter because of this. My fuel mileage improvement was right about what was predicted in independent testing. I could not be more thrilled and plan to use it henceforth. I also plan to replace the exhaust with a free flow 4" exhaust and hope that helps. My goal is to be able to carry my camper with no loss in fuel economy over what I had before.
  • 2012 3500SRW crew cab 6.6 LML today 23.7-24.2 mpg on the hwy. 60-70mph keeping the foot off the floor. Empty 8 ft' bed with tonneau cover.

    City is a little different. I have not taken it easy enough to really find out.

    Modifications - Airaid intake system. Engine light on for good. DPF sucks. To must air sucking past the MAS air flow sensor. 3 burns per tank. Stock truck. rotella T.

    pre installation of air filter trailering of 13500# 40' 11.5 - 12.5mpg pulling with stock intake in the summer
  • Well this is good news about your 2012 3500SRW LML diesel. I think that is very good mileage for one of the newer models. I have a 2006 2500LBZ and can get 25 mpg highway under 65mph without cruise control and 23-24 with cruise. However my city mileage is 16-20 varying mostly with the seasons. I have no modifications but do run full synthetic oils and lubes. I have also lifted the front by 1.5 inches so far. I do plan to beef up my tranny lines and front suspension with aftermarket parts and hopefully add an Edge systems engine controller. If I ever need a tranny I am going ATS with controller.
    I tow an 18,000# load including trailer, 38 foot sailboat + a lot of its gear getting 12 - 15 mpg depending on speed and terrain.
    My truck gets great mileage at 52-55 mph but I rarely get to drive that slow.
  • cstyle7cstyle7 Posts: 1
    02 GMC Durmax LB7.  S&B cold air intake is the way to go. K&N does not do well with Diesel trucks. I however love K&N in my gas trucks.
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