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Significant drop in fuel economy... ideas?

Discussion in 'Technical Chat' started by eltaco, Dec 22, 2011.

  1. Dec 22, 2011 at 8:59 AM
    #1
    eltaco

    eltaco [OP] Well-Known Member

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    I'm driving (not as I type this) back home to visit family for Christmas and have been getting significantly less gas mileage than what is typical for my truck. I do have 285s on the truck, but have been running them for a couple of years. I typically get between 18-19mpg on the highway, but have only seen 12-14mpg on the 750mi I've driven thus far... what could be causing such a significant decrease?

    Ambient temps have been 22-34F.
    I'm driving interstate at 77-82mph. RPMs are constantly at 2100-2200rpm... flat land so no climbing.
    Loaded with two adults, suitcases and dog.. fairly light load.
    Tires inflated to 29/32.
    Engine and differential oil are fresh. New air filter prior to leaving.
    Truck sounds good and is running strong... no obvious issues.

    Any thoughts?
     
  2. Dec 22, 2011 at 9:00 AM
    #2
    98tacoma27

    98tacoma27 is gooder 'en chicken Moderator

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    Winter gas with the added weight. And your tires seem a little under inflated (to me).
     
  3. Dec 22, 2011 at 9:02 AM
    #3
    chadderkdawg

    chadderkdawg Don't ask questions you don't want the answer to..

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    This too
     
  4. Dec 22, 2011 at 9:03 AM
    #4
    98tacoma27

    98tacoma27 is gooder 'en chicken Moderator

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    5100's all on fours
    Good point. I missed that
     
  5. Dec 22, 2011 at 9:05 AM
    #5
    dexterdog

    dexterdog My pee parts itch

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    Speed, tire inflation(which seems pretty low considering they're 285s) winter fuel, and possibly plugs(is it time to change them?) are probably your main issues.
     
  6. Dec 22, 2011 at 9:07 AM
    #6
    himmy33

    himmy33 Well-Known Member

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    Winter gas. I saw a sudden drop in my gas mileage as well. I use fuelly and it was amazing to look at the chart and see the difference when they switch to winter blend fuel.
    Check in out
    http://www.fuelly.com/driver/himmy33/tacoma
     
  7. Dec 22, 2011 at 9:08 AM
    #7
    chadderkdawg

    chadderkdawg Don't ask questions you don't want the answer to..

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    Is that for real? Whats so different about winter gas?
     
  8. Dec 22, 2011 at 9:13 AM
    #8
    eltaco

    eltaco [OP] Well-Known Member

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    I know the speed is at the top end of what I run... still don't think I've ever seen below 15mpg with my tire pressure as it is currently. What pressure do y'all recommend for 285s while not losing too much winter traction?

    You really think winter fuel makes that much difference? Sheesh... news to me.
     
  9. Dec 22, 2011 at 9:22 AM
    #9
    jeremy_283

    jeremy_283 Super Member

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    Have you checked your muffler bearings lately? If your muffler bearings are not properly maintained the EGE (exhaust gas evacuator) will not spin freely and there will be increased back pressure on your pistons and valves causing a larger load on your engine. This causes increased fuel consumption and leads to worse gas mileage.
     
  10. Dec 22, 2011 at 1:14 PM
    #10
    BlueT

    BlueT Well-Known Member

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    I moded 1999 Taco so much it had turned to Land Cruiser
    Yep thats easy
    Here is your problem
    [​IMG]
    Where
    [​IMG] is the force of drag,[​IMG] is the density of the fluid,[12][​IMG] is the speed of the object relative to the fluid,[​IMG] is the drag coefficient (a dimensionless parameter, e.g. 0.25 to 0.45 for a car)[​IMG] is the reference area,
    more here
    http://en.wikipedia.org/wiki/Drag_(physics)
     
  11. Dec 22, 2011 at 8:10 PM
    #11
    jeremy_283

    jeremy_283 Super Member

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  12. Dec 23, 2011 at 1:53 PM
    #12
    himmy33

    himmy33 Well-Known Member

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    Sure is real. What they do/blend to the gas is beyond me. Not sure what they are adding...
     
  13. Dec 23, 2011 at 9:37 PM
    #13
    MountainEarth

    MountainEarth Well-Known Member

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    That's a HUGE drop in MPG. And considering he's running the same tires he's been running for a couple years (with good mileage), the tires or tire pressure wouldn't be it. Nor would oil or diff fluids or air filter (says all new). And witner blends might drop your MPG a couple points, but not from 18-19 to 12-14. So the mystery stands. I'd say the OP has a very legitimate complaint.
     
  14. Dec 24, 2011 at 8:23 AM
    #14
    krap22

    krap22 Well-Known Member

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    anyone have a link to this "winter blend" and have proof that it exists?

    i think it has more to do with the low temps and the fuel not atomizing as well as the air is more dense at lower temps so it creates more wind resistance.
     
  15. Dec 24, 2011 at 8:28 AM
    #15
    Warputer

    Warputer Dirt Road Inspector

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    A little lift & some extra steel....
    Even with my stock truck, I've never seen 18/19mpg while driving 80mph.
     
  16. Dec 24, 2011 at 8:47 AM
    #16
    08pretaco

    08pretaco Almost there

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    tire pressure does not increase with tire size. Pressure is more of a constant, the volume of air increases but the pressure in a 37x12.5 (be it 29) is the same as a 225/75 at 29...its just an increase/decrease in volume.

    Shit my tires are at 20 psi in order to pass the chalk line test. And I get 24 mpg, 4 cylinder
     
  17. Dec 25, 2011 at 3:03 PM
    #17
    eltaco

    eltaco [OP] Well-Known Member

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    Thanks... this was my thoughts exactly. I only provides all that info in case something sounds way off.

    I drove one stretch of highway at 45mph due to snowy conditions, and I pulled 15.8mpg through that section... still nowhere near normal for me.

    I'm headed back home tomorrow, I'm assuming everything stays the same, unfortunately. This trip got a lot more expensive than I anticipated at 2000 mi round trip.
     
  18. Dec 25, 2011 at 3:33 PM
    #18
    tx novice

    tx novice Foward momentum

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    :D yeah and check your turn signal fluid too. Oh , and your piston return spring . You might not be getting enough torque from your engine .
     
  19. Dec 25, 2011 at 4:48 PM
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    2008taco

    2008taco Well-Known Member

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  20. Dec 25, 2011 at 5:08 PM
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    KenLyns

    KenLyns Lord of War

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    OP, how are you measuring the MPG?
     
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