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Chevy Silverado and GMC Sierra Duramax Fuel Mileage

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  • goldenjgoldenj Posts: 2
    I have a 2005 2500HD Duramax 4x4 with crew cab, when it was purchased we were told to expect 18-20 mpg, but have never seen any thing close. Have taken it to the dealership they checked it and at first had a computer problem with it, after several weeks they got a fix for the problem, but did not fix the mileage problems. They told us after the engine got broke in it would get better all the time, but have not seen that happen either. The truck is a great one, the ride is wonderful, and the power is unbelievable. It now has 42000 on the engine, but the best I have seen is 17mpg and 8 mpg towing. I have considered getting a chip. A friend has one that he used (El Diablo) and was getting 23mpg on his 2004 truck. Any suggestions would be greatly appriciated!

    Love the truck hate the mpg :cry:
  • fueledupfueledup Posts: 64
    I owned a 2003 2500 4x2 crew cab long bed duramax& allison, always got 15.5 city & 19.5 hwy, put 60,00 miles on it. traded it in june 05 employee discount too good to pass up. now own 2005 4x2 crew cab short bed duramax&allison, 14.5 city & 18 hwy, 15000 miles am disappointed in mpg reduction who the hell knows why .
  • spademanspademan Posts: 14
    I have been asking around about chips myself. A mechanic told me not to get the diablo because it makes the allison shift really hard, and is therefore hard on the tranny. He did say that you can expect from 2-5 mpg better!
  • spademanspademan Posts: 14
    I've also found that if you install an aftermarket air intake, and change the exhaust you'll see an increase in mileage also.
  • I have better throttle response and a bit more low end, but mileage is about the same. Pulled my 16ft Pace(low weight load,2k trailer wt plus 1 Quad) and got 15.1 MPG @ 60 MPH this past weekend.
    I have
    1)Bullydog Pup re-programmer
    2. Afe 7 stage high flow air filter
    3. 4 in stainless exhaust
    2006 4X4 2500HD Duramax,6 speed,Crew Cab, SB 265 tires 3:73
    22.5MPG @ 55MPH, 18MPG@ 75MPH Combined 16MPG last 3 tanks
    10K miles
  • spugspug Posts: 2
    Problem resolved. I contacted the dealership, who spoke to GM engineering in Detroit. Corporate advised of a kit to be placed on the exhaust system. Bottom line is the kit once installed stopped the howling noise.
  • Some reasons why you don't get good mileage as other such as year,4-wheel drive or 2 wheel drive,tires,and the way you just drive. If getting bad mileage go take it in and get computer reprogrammed and it should help also. Another is chips too such as banks,edge,bully dog,ect but the edge and bullydog void warranty when you use them and can also screw up truck in long run. But i've never heard of gettin 8mpg cause we got 2002 2500hd duramax ext. 2wd gettin 17-18city/20hwy but newer ones might get little less cause of new 360hp and 650lbs torque but dodge cummins gets good cause inline 6 but not as much power n torque as new duramax.
  • I have a 2005 GMC K2500 HD SLT crew cab short bed w/ LLY DuraMax and Allison 5-spd. The only way you will ever get 24 mpg out of this combo is if you baby it. If I never go over 50-55 mph and always stay on flat highway and never get stuck at stop lights I MAY get 23-24 mpg. However, I commute 100 mi. round trip on southern Indiana highways (lots of hills and several small towns and stop lights) 4.5 days / week. I currently average 17-18 mpg cruising at 70 mph. I think that is GREAT for a truck that weighs over 6000 lbs. and has 310 hp and 590 ft./lbs. It is all about compromise. Do you want power or do you want fuel economy? You cannot have your cake and eat it too. Power takes fuel. Also, at speeds over 55 mph wind resistance becomes your greatest enemy. Your wind resistance increases as a square of your speed, which means that for a small increase in speed your wind resistance (or drag) increases dramatically. I have put 20,000 miles on my DuraMax / Allison in less than 9 months and I still love it. The biggest thing that they are doing w/ the GM trucks recently is that they have added an extra overdrive to the Allison. It is now a 6-spd. auto with 5th and 6th being overdriven. Now with the extra overdrive to drop the revs at 70 mph you may be able to squeak out 20+ mpg if you keep it around 70 mph and don't try to race too many Mustangs. Right now at 70 mph in my truck I'm hitting about 2100 rpm in 5th (OD). If they get that to drop to 1800-1900 then you will definitely gain some fuel mileage. Plans for the DuraMax in the near future also include twin turbos that will put it well over 400 hp and 700 ft./lbs. of torque! By the way, Mustangs go down easily in the stoplight wars. Some kid in a 03-04 GT 6-spd. was giving me the look and power braking it at a stoplight headed out of town on a 4-lane highway and when it turned green I let him have it and he was at least 2-2.5 truck lengths behind me when I let off at 75 mph. He had been stoplight racing all the other cars through a small town and I think he was a bit surprised to lose to a 6000 lb. truck that was almost twice as long as his car! Sorry for the rambling, but I love my DuraMax...can you tell?
  • akenatenakenaten Posts: 122
    Does anybody use synthetic oils? Are they even made for a diesel? :confuse:
  • burtvburtv Posts: 1
    I have a 04 Duramax LLY, crew cab short bed automatic, 6 inch lift 12.5 x 35 tires. My speedometer is off by about 8+ miles an hour in other words when it reads 70 mph I am actually going about 78 mph. My gauge says I am getting about 13.2 mpg. I try to drive sanely about 98% of the time. This gauge doesn't change very often like once every six months, if that often, is this normal. I took it to the dealer (under warranty and still under warranty) Alfred Matthews in Modesto (they did the lift and tires) and they said that there was something wrong with computer and the speedo could not be reset. I spoke to three other dealers and they told me Allison (and I confirmed this on the Allison website) locked out the ability for a dealer to change the tire size but could be done with an aftermaket computer. Anyone do this adjustment and if so what programmer did you use?
  • KCRam@EdmundsKCRam@Edmunds Mt. Arlington NJPosts: 3,495
    There are several synthetic oils approved for diesel use...

    - Shell Rotella T
    - Mobil Delvac-1/Mobil 1 Truck and SUV
    - Valvoline Premium Blue Extreme

    kcram - Pickups Host

    KCRam - Pickups/Wagons/Vans+Minivans Moderator

  • igop71igop71 Posts: 3
    What about AMSOIL synthetics... are they not approved for diesel use? I've only changed the oil of my 05 Duramax once (with AMSOIL 15W-40) since I got it last year and is scheduled for one soon. My next question is how often are you supposed to be changing fuel filter? I don't drive that much and only have a little over 10000 miles on my truck since July last year.
  • nezzy711nezzy711 Posts: 2
    I just bought a used 2003 silverado 2500hd duramax and have three concerns. I am averaging 14mpg. Is this normal. Also on hard accelaration it blows black smoke out of the exhaust. What might this be. And it has an allison automatic transmission and in fourth gear at 2500rpm the engine sputters, backfires and misses. Please any advice is appreciated.
  • KCRam@EdmundsKCRam@Edmunds Mt. Arlington NJPosts: 3,495
    Yes, AMSOIL is indeed SAE certified, although the major diesel engine manufacturers have put their stamp of approval on the other brands I mentioned.

    As far as fuel filters, if you don't drive much, you should probably replace it annually. Algae and other deposits can form in diesel fuel when it sits for extended periods of time, and that needs to be cleaned up by a filter that's up to the job when you do need the truck.

    kcram - Pickups Host

    KCRam - Pickups/Wagons/Vans+Minivans Moderator

  • outakashoutakash Posts: 2
    I was talking with a friend just yesterday about the tail gate in the down position and how Myth busters busted the myth about better fuel mileage with the gate down. Not true! fuel mileage decreased. Seems like the engineers have figured out that by keeping the tail gate up creates a sort of air bubble over the bed that the air on top passes over. Try taking the tonneau off and testing it again. I have a 2002 with a tonneau and generally get 18 but have gotten 19.3 (got a little over 57K miles on it).
  • akenatenakenaten Posts: 122
    I have a 2006 Sierra 2500HD and I've noticed a "howling noise" when I accelerate when the truck is still fairly cold. For some reason I think it's the air intake but I don't know that for a fact. The noise stops when the truck is warmed up. :)
  • akenatenakenaten Posts: 122
    I have a new Duramax with about 1000 miles on it and I'm getting 19 in mixed driving.
    I want to put a billet grill on my Sierra 2500.Will that effect the cooling capacity in any way?
    And I noticed that next to the fuel tank there appears to be a radiator. Why? :confuse:
  • rseeborseebo Posts: 12
    I have the 05 diesel and added the banks 6 gun tuner. I have just broken 40k in mileage and average about 21 - 22 MPG's on level 6. I drive 85 miles per day and up the Cajon Pass, which is about a 20 mile climb from Sea level to 4500 feet. I have had several issues with limping the tranny from getting on it to much and just having to pull over and shut er down and restart to reset. Now I am having an issue with an error stating low fuel rail pressure. Is this due to bad fuel filters? I get it whenever I have to move fast out of a situation.
  • ddf1ddf1 Posts: 18
    My guess is the low fuel pressure is due to the power upgrades. Did u install a lift pump? That could fix it. The duramax doesn't have a lift pump and when you add gobs of power the stock fuel system can't keep up. BTW I just added a BD Intimidator programmer set on 80 hp and 200 lb torque, 4" Corsa exhaust and got 21 mpg. I was getting about 15mpg with 285 tires.
  • rseeborseebo Posts: 12
    No I didn't. I am not sure if banks has that as part of their package. One would think that they would if the power gains were to much for the stock system to handle.

    I was told that the fuel filter needs to be changed at a recommended mileage of 15K. So I am going to try that tomorrow and see what happens. Thanks for the input though.
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