VW Jetta MKIV/MK4: Poor Gas Mileage |Volkswagen Bora
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Thread: Poor Gas Mileage

  1. #1
    Senior Member lifelikechild is on a distinguished road lifelikechild's Avatar
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    Jan 2010

    Default Poor Gas Mileage

    The gas mileage in my '01 Wolfsburg has gone way down. No codes. Not sure where I should begin? Air filter's clean.. Got 62k on it

  2. #2

    Default Re: Poor Gas Mileage

    Quote Originally Posted by Boost Addicted View Post

    Winter blend fuel is mixed with extra ethanol, and other chemical compounds that are a higher octane rating, but have less heat energy (BTU's). It's common to loose a good 8% fuel mileage, and with a 1.8T, 25-27mpg average city/highway isn't uncommon. Anything less I might start worrying.

    But there are countless things that could cause poor fuel milage..

    -Dirty air filter
    -Dirty fuel filter
    -Dirty injectors
    -Dirty MAF sensor
    -Fouled spark plugs
    -Improperly gapped spark plugs
    -Bad coolant temperature sensor
    -Bad oxygen sensor
    -Dirty engine internals

    etc..... Basically anything that isn't working in perfect harmony.

    For anyone interested in this....

    Driving habbits make probably one of the biggest differences. Whenever you can use cruise control, do it. Slowing down then speeding back up will cost you more fuel than anything, even if its just a few mph/kph. There's also a worldwide myth that says accelerating slowly saves fuel... And it's total bs. If you guys have the MPG program in your cluster where it gives you heads up information, test this out if you don't believe me. Two different days, same route, accelerate up to speed slowly, then steady out. The other day, accelerate quickly up to speed, and steady out. Guarantee you you'll see a difference, and sometimes a major difference if it's a significant route.

    If you have a manual transmission, don't cruise under ~2300RPM's. I cruise at 2500-3000RPM's. Fuel mileage is load based, NOT RPM based.... There's always hills and bumps in the road, and when you have to speed up, its far easier to do it when your engine is at higher RPM's. Easier for the engine = less fuel consumption. The less your foot is on the throttle, the better off you are. And no, constant ''high'' RPM's don't wear your engine faster.

    And finally (manual transmission only), when going downhill or coming up to a stoplight/sign, stay in gear! With your foot off the throttle and the transmission in gear (above 1200RPMs), your injectors turn off.... That means you use zero fuel. Cruising to a stop in neutral will get you decent fuel mileage as well, but you're still using quite a bit of fuel to idle.
    If you need more info, these two threads explain a lot.
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  3. #3
    Junior Member albert0h is on a distinguished road albert0h's Avatar
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    Default Re: Poor Gas Mileage

    Put some seafoam in your engine oil. I did it the other day and it gave me like a extra 2 to 3 miles.

  4. #4

    Default Re: Poor Gas Mileage

    Do you add the seafoam drive couple of hundred miles before an oil change or driving with the seafoam in the engine?

    Do you think that's bad - My 03' GLX V6 was getting something like 12 MPG in town... ouch!!

    It's gotten better now, and I am getting something like 17 MPG in town. I just got two new Bosch O2 sensors, but haven't had them installed yet. I will probably swap out my fuel filter as well. It has new plugs (NGK) and an air filter 4 months ago.

    Let's see the difference after I swap out the O2 sensors and the fuel filter. I might replace the coolant temperature sensor as well.


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