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Thread: horrible mpg

  1. #1

    Default horrible mpg

    i have a 2000 1500 4x4 5.3 silverado and i am getting 9-11mpg city and highway. i have a 26gal tank and get around 250-310 miles per tank.

    i have no idea why i have such bad mpg.

    i am running 305/70/16 with stock gearing. custom exhaust, CAI, tuneup done in january(fuel filter, CAI install, plugs, wires, oil, oil filter, seafoamed through gas tank and vacuum line.) just changed the TPS.

    and another thing which i do not know if this is a factor in mpg but my gas gauge doesnt seem to work...the low fuel light is always on when starting and turns off and shows amount of gas after about 5 mins of driving. and when i fill my tank it shows empty even when driving.

    ive been stumped on this for months and cannot find the solution.

  2. #2
    Sr. Engineer
    Join Date
    May 2009
    Manitowoc, WI


    The big tires kill mileage. Mine dropped from 16-17 with stock tires to 12-13mpg with 285/70/17's, your tires are even larger (those must be close to a 35" tire!), plus if you have any lift kit on it that isn't helping it either.

  3. #3


    Quote Originally Posted by Greg84 View Post
    The big tires kill mileage. Mine dropped from 16-17 with stock tires to 12-13mpg with 285/70/17's, your tires are even larger (those must be close to a 35" tire!), plus if you have any lift kit on it that isn't helping it either.
    its about a 33 inch tire. 32.8 to be exact

  4. #4
    murdog94's Avatar
    Join Date
    Feb 2008
    Cloquet, Minnesota, United States
    Blog Entries


    Hey Silverado have you tried a programmer to get the shift points back to where they need to be also to get your speedo back to the correct reading. Because running that much taller of a tire makes your speedo read slower than you are going and then your odo actually shows less miles that you have actually gone.. Also changing the pump module as discussed in other threads should fix your gas guage.. and that will help also so you know better to how far youve gone and how much fuel you have left.


    1997 Chevy S-10 Blazer 4X4 with 330K miles and counting (Hunting rig).

    2009 Saturn Aura XE (wifes car)

    2011 F-150 Crew 4X4

    "Hold it to the floor till you see God.... Then Brake!!!!"

  5. #5


    have the ethanol in your fuel tested. biggest mph killer

    get a good injector/carbon clean, not the stuff in the cans at the parts store

    you more than likely have some broken wire strands in the fuel sender or high resistance in the signal circuit

    05 silverado shortbed

  6. #6

  7. #7

    Join Date
    Jun 2006
    River Ridge Louisiana-4 miles W of New Orleans-didn't flood-water stopped 800 yards away.


    Have you corrected your MPG for tire height?
    Your new tires must be at least 1.5" taller than the old ones.

    If the new tires are say 3" taller than stock your actual mpg is 10mpg X 33/30= 11 mpg
    Your actual distance traveled would be 10% more also.

    If the difference in height is more like 1.5" then it is .5mpg off.

    I'm guessing your original tires were 265/70 16?

    So these 305/70 16 are two times (305-265) times .7=54mm or 2.2" taller or 6.6% taller.
    Your real mpg is about .66 mpg more.
    Your real distance traveled is about 6% farther than your odometer says.

    If this was already discussed-sorry-I should have read more closely.

    10-11 mpg isn't really bad for a 4x4 GM 5.3 in pure city driving. Now 11 mpg is pretty bad for hy driving-With stock profile "street type" no big mud lugs tires you should get 15 mpg or so.

    Bigger wider tires do decrease real mpg-especially if they are mud type off road type tires.They are wider-more wind resistance-and usually have higher rolling resistance.
    Last edited by phoebeisis; 05-18-2010 at 08:10 AM.
    1998 suburban-
    1/2 ton

    199500 miles

  8. #8


    wow thats some great info right there. thanks man!

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