99 C1500, 5.7 fuel mileage

Discussion in 'Chevy C/K Truck Forum' started by 59diesel, Apr 23, 2012.

  1. 59diesel

    59diesel New Member

    Just wondering if someone can gimme an idea of what mileage I should expect.. I have a 99 C1500, extended cab, auto, 5.7 Vortec with 118K total on it, all 100% original except for the tires, have gone to a 31-10.50-15.............recently I have done a complete tune up, cap, rotor, wires and plugs, along with pcv and fuel filter......I keep it very well maintained and it runs like a new one (and drives like a new one now with complete front susp rebuild).........One thing I CANNOT seem to find a timing tab...if it is there its where I cant see it........hook a timing gun to it, and the timing mark is dead on straight up on the damper.......if you move the distributor more than just a little bit, the "service engine soon" light comes on.........retard or advance, move it back and the light goes off............anyway, like I said, it runs great and the plugs look good, I average about 15-15.5 mpg on regular unleaded with kind of a mixed driving, highway/city.....it does show to have a rearend code of GU6, which I think should be a 3.42 ratio.............any thoughts on this mileage, or ideas on the timing tab ?
     
  2. rileyjr16

    rileyjr16 Rockstar 3 Years 1000 Posts

    I'm gonna go out on a limb and say about 14 highway/city

    ---------- Post added at 03:25 AM ---------- Previous post was at 03:24 AM ----------

    I put 265/75/15s on my 97 Cheyenne with a 4.3 and I got about 13 highway/city which I still regret doing.
     
  3. revscott

    revscott New Member


    I put 265/75/15s on my 97 Cheyenne with a 4.3 and I got about 13 highway/city which I still regret doing.[/QUOTE]

    I switched to the smaller 235/75 R15's, got a little better mileage, but dont like the look the tires look really small compared to the 265's. I want to switch back!
     
  4. rileyjr16

    rileyjr16 Rockstar 3 Years 1000 Posts

    I switched to the smaller 235/75 R15's, got a little better mileage, but dont like the look the tires look really small compared to the 265's. I want to switch back![/QUOTE]


    Go 265 but go with a smaller ratio if you want the width.
     
  5. murdog94

    murdog94 Epic Member 5+ Years 5000 Posts

    Alright im gonna touch on the timing. do not mess with it. It is set by the computer and the only mechanical link is stabbing the dist. at #1 TDC. The rest has to be set by a shop or if you have the correct computer to do it. there is no timing tab.
    You are getting right in line what i would expect. on a long highway drive i would expect 18ish, and pure town about 13-14. So you are getting average milage.
     

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