why am i getting bad gas mileage

Discussion in 'Trucks and Trailers' started by JML, Feb 7, 2001.

  1. JML

    JML LawnSite Senior Member
    Messages: 415

    i have a 2000 gmc 3500. 5.7l, auto, 4x4, 4.10 rears. i average 9 to 10 gallons around town. i am not heavy on the pedal at all.i talk to other guys and they get 12 to 13 around town with the same truck. why is my truck doing so bad. i have 14,000 miles on it. thanks

  2. Jeff's Classics

    Jeff's Classics LawnSite Member
    Messages: 78

    The other guys you talk to may not have 4.10 gears, those are pretty steep. They're great for pulling, hill climbing, acceleration, etc but not so great for the mileage. Also, consider that you have a one-ton 4X4...you are not going to get much better than 10 or so. There's a guy here in my office with a one-ton 4X4 crew cab that is getting about 10 mpg, mostly commuting but not alot of stop and go. Mileage has alot to do with driving style, but you can ask the dealer if there is a newer computer program for your engine, maybe they have updated something.
    Tough question to answer.
  3. RTallday

    RTallday LawnSite Member
    Messages: 214

    If it makes you feel any better, i have a 1979 Chevy 3/4 ton, 4X4 (K-20) And i have a 350 with the 4 speed, and i have 4:10s too. I only get 10. On the highway, maybe i get 12 ish, i really dont know. I figured id try to help.

  4. 75

    75 LawnSite Senior Member
    Messages: 992

    Rich, Jeff, Joe - same here. '75 GMC C-35, 350/T400, 4:10 dually axle, 10 mpg or so tops. Big, solid trucks = less mpg. But the advantages outweigh that disadvantage - that's just my opinion, of course.
  5. plowjockey

    plowjockey LawnSite Senior Member
    Messages: 332

    Since we're comparing I have an 85 GMC K-2500 with 4:10's and I'm getting 11.25 mpg. The C-70 dump on the other hand with the 427 cid is a very friendly vehicle because it just LOVES gasoline. I won't even hazard a guess what it gets I have not checked the mileage yet (just got it).

  6. John DiMartino

    John DiMartino LawnSite Silver Member
    Messages: 2,555

    10 isnt that far off what it should get.Most new 2500's have 4.10's.Do you let it warm up long?,you drive agressive or accelerate hard,low tires?,There are a lot of things that will hurt your mileage,short trips are the worst,around town driving mileage is terrible on any 4x4 gas motor,3/4 ton pickup,anyone telling you they get much better is full of you know what.
  7. Alan

    Alan Member
    Messages: 1,185

    Last I knew 4.10 was as tall a gear as you could get in a 3500 series. I've seen most 2500 come through with 3.73, that seems to be a good compromise geat although I think I would prefer 4/10 with the OD transmission, revs are bit low in overdrive at highway speeds for my tastes. Worst case I saw was an 89 2500 that a buddy had, 3 spd auto and 4.10,, that rig liked fuel.
  8. John DiMartino

    John DiMartino LawnSite Silver Member
    Messages: 2,555

    Alan 4.56's are available in the C/K series,with the 454,not in the new Silverado though.
  9. I have a 4.10 limited slip in my 1992 c1500. I just put a new set of 30.5 tires on last fall to knock the revs down at bit on the highway.

    With a 4.3v6 and a 4 sp auto I get around 15 mpg pretty much loaded or empty.

  10. 85w/350

    85w/350 LawnSite Member
    Messages: 244

    15mpg out of a 4.3v6? Man thats the pitts...a relative has a 94 chevy ex-cab sport bed with a 4.3 v-6 when we pull his 15foot bass boat behind it loaded down with fishing and water sports equipment and the ex-cab loaded with people we still get about 15 in the city and 20-22 on the interstate. You might look at getting something other than those 4.10's maybe like 3.73's I bet your truck gets up off the line quick but the highway speed rpm's must be outrageous

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