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Thread: DIY : Fuel Economy

  1. Top Of Page | #1
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    DIY : Fuel Economy


    This thread is intended to be a consolidated source of information about gas mileage in our cars.

    If you have any questions pertaining to MPG, please post them in this thread.

    Please keep one thing in mind. You do not drive a 3 cylinder Geo Metro. You're NEVER going to get 35+ MPG. On a well running Second Generation Legacy, you can expect up to mid 20s

    Things to replace

    • Spark Plugs
    • Spark Plug Wires
      Faulty plugs and wires can affect your MPG by 10%
    • Air Filter
      A dirty air filter can affect your MPG by about 5%. They are usually less then $10, so just replace it with a new one. A dirty one basically "chokes" your engine.
    • Fuel Filter
      Same deal as the air filter, but a little more expensive....usually around $20
    • Upstream O2 Sensor (before cat converter)
      The only O2 sensor that affects your MPG is the upstream sensor before the converter (closest one to the engine). With age and use, they tend to wear out and not function as good as a new one. Replacing an old O2 sensor can sometimes help out your MPG. DO NOT use a "universal" one.
    • Engine Oil
      For fuel economy, its best to run lower viscosity oils. I personally run Mobile 1 Synthetic 5w30. Heavier oils put more resistance inside the engine, directly affecting fuel economy.
    • Transmission Filter / Fluid
      For automatic transmissions, dirty fluid or worn out fluid can cause the transmission to work harder.
    • Rear Diff Fluid
      Clean GL5 has less resistance, and allows the gears to spin more freely.
    • Pulleys
      Replacing your stock crank pulley with a lighweight (not undersize) pulley will help you out a bit.
    • Flywheel
      For 5 speed cars, installing a lightweight flywheel will help out. It reduces rotating mass on the engine. Basically does the same thing as a lightweight crank pulley, but on a much bigger scale.
    • Coilpack
      Replacing your stock ignition with MSD will burn your fuel better, resulting in better MPG

    Things to clean

    • Mass Air Flow Sensor
      If this is dirty or not functioning correctly, your air / fuel mixtures will not be right. This will cause a drop in fuel economy.
    • Idle Air Control Valve

    • Throttle Body
      Cleaning the throttle body will give the air coming into your engine a more direct path without resistance.
    • Fuel Injectors
      Run a bottle or two of STP Fuel Injector Cleaner. Clean fuel injectors work MUCH better.
    • Trash / Excess Luggage In Your Car
      All the extra weight in your car affects your gas mileage. The more weight is on the wheels, the harder the engine has to work to get the car moving....and keep it moving


    • Alignment
      If your car is out of alignment, there is more rolling resistance on the tires, causing the engine to work harder to move the car. If your alignment is out in the rear, its almost like your back tires are pulled, instead of rolling straight.
    • Tire Pressure
      Higher tire pressures have less rolling resistance. I wouldn't go above 35PSI though.
    • Wheel Bearings
      A bad wheel bearing will cause the same kind of problems as low tire pressure.
    • Brakes
      Brakes that "stick" and don't release like they should cause the engine to work harder to start rolling the tires.
    • Cruise Control
      Use your cruise control. When you drive at a steady speed, you use less gas.
    • Lead Foot
      Its been said that your fuel economy drastically drops after 55MPH. Don't drive like a bat out of hell.
    • Route Selection
      What roads you travel on have a big impact on your gas mileage. Try choosing straight, flat roads instead of hills and curves. As well, the more "stop and go" traffic you're in, the more gas you will use.
    • Check Engine Light
      Is your check engine light on? If so, its going to directly have an impact on your fuel economy. Get whatever is wrong fixed, and you will see an increase in fuel economy.

  2. Top Of Page | #2
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    Great tips. I have found my 08 LGT get better MPG on cruise while in "S" mode than "I " mode. Seems less shifting???

    Sent from my XT907 using Tapatalk

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  4. Top Of Page | #3
    Basic Member putineski's Avatar

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    Re: DIY : Fuel Economy

    Great reminder.


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