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My car is eating gas

  1. Aug 16, 2013 #1
    I do not know what has been going on lately, but my car (a Saturn Aura 2008 with 4 cylinder ~170hp) has been eating gas alive. My car currently struggles to reach higher speeds, even 40 mph. Within the first two gears the automatic transmission usually shifts around 3500rpm. I do have about 200lbs worth of weightlifting equipment in my car, but it should drop my mpg so drastically. According to the computer I am averaging about 21mpg, when I should be getting 25-28 around down and 30ish on the highway.

    Any ideas?

    I did put some seafoam in the tank a few weeks ago. Im not sure if it helped. Im also thinking that my transmission fluid may be low.
  2. jcsd
  3. Aug 16, 2013 #2
    Do you usually drive alone? 200 lb of weightlifting equipment (while maybe not dropping it that much) will act as if there's another person in the car; 200 lb is roughly a 5% increase in weight, which is not insignificant (especially for a 4-banger).

    Are you sure about the 25-28 around town if you're seeing 30 on the highway? From my experience, local driving is significantly lower than highlway driving.

    I've only used seafoam for my vac lines, and I only saw benefits. Has your exhaust sounded louder recently? Any change in driving habits? Have you checked your air filter recently? Could be fouled spark plug(s), too.

    EDIT: I've also heard, anecdotaly, that if there's significant carbon buildup being cleared, it can accumulate on the O2 sensors and foul them. A busted O2 sensor will screw with your mpg bigtime.
    Last edited: Aug 16, 2013
  4. Aug 16, 2013 #3


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    Plugged fuel injectors can cause this problem. Don't want to inject raw fuel.
  5. Aug 16, 2013 #4
    It might be closer to 25, I have the original sales pamphlet in my car. The biggest issue is that the car is simply not accelerating. I have to really push the pedal to get it to over 40. It may not be the mpg is bad, so much as the engine is operating at a higher RPM for a longer duration. I talked to my dad about it and he suspects the injectors may be dirty (the car was rebuilt after being total and sat in a garage for awhile). It almost seems like the issue is with the first 2 (maybe 3) gears.

    I would also like to add that this problem has been slowly but progressively getting worse.

    Airfilter checked out and is clean
    No change in driving habits

    You think another can of seafoam would help?
  6. Aug 17, 2013 #5
    To start with I'd go back to basics air-filter, fuel filters and plugs is your transmission fluid at the correct level are you running hot (cooling system).
  7. Aug 17, 2013 #6
    It's a modern car so problems will likely throw up obd codes. Start by giving it a service and getting it scanned for codes is a good step.

    My first bet would be a fueling issue. It really could be anything though. Also you can't really compare drive cycle economy with real world economy.
  8. Aug 18, 2013 #7

    jim hardy

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    Anything made after 1996 has that OBD computer-code-reader connector adjacent steering column.

    Do you frequent auto parts stores? Most of them will let you use their code-reader in their parking lot.
    A cheap reader costs only around forty bucks at discount places like Harbor Freight.

    The computer will give you good clues as to anything it sees. Let it help you.
    Your symptom sounds just like my Dodge when the Oxygen sensor went out at seven years old. Computer detected it and gave the code. Local mechanic wanted to replace the fuel pump.

    Sites like this can help you interpret the codes

    the ones on my Ford Escort were pretty self explanatory, hardest part of repairs was finding where they hid the darn sensors.
  9. Aug 18, 2013 #8
    I have a Saturn that had similar problems. Turned out the EGR valve had gone bad. Do you have a rough idle?
  10. Aug 18, 2013 #9


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    some simply things to do before you monkey around.
    These things would probably not show up on the OBCD or Check Engine.
    You just might be lucky that a walk around the car when idleing will give you a clue.

    Check your oil level and change with the cars maintenance schedule in mind
    Check tire pressure.
    Is the transmission supposed to shift at 3500 rpm? or normally at a lower rpm?
    If lower, then electrical and hydraulic signals to or within the transmission may be a problem.
    Maybe the bands are wearing out and one day you won't be able to go anywhere. Any odd smells.
    Is one of your brakes on a tire or more releasing - a stuck brake pad sucks power. any smell.
    Exhaust plugged. check tailpipe for any flow coming out. Calalytic convertor plugged.
    Exhaust - any soot or smoke coming out - ie rich mixture or burning oil -> O2 sensor might detect that.

    I have a Hyundai car here that will drive me to work, but will not drive me home. It just konks out and will re-start only after a 2 to 3 hour spell. Haven't figured it out yet.
  11. Aug 18, 2013 #10

    jim hardy

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    I had an outboard boat motor with with same exact symptom. Ran it one night with motor cover off, saw sparks along a hairline crack on the ignition coil. I surmised it was temperature sensitive due to thermal expansion - crack got wider..

    If yours has a single coil and distributor, try the "run it in the dark" trick.
    Even a "Nothing noted" is one more piece of the puzzle.
  12. Aug 18, 2013 #11
    The catalytic converter is damaged and needs replacement. I had exactly the same problem with mine about a year ago. I had checked everything else and the last I checked was the catalytic converter. I replace it and everything worked like charm.

    The ceramic inside the converter is broken to pieces and blocks the flow. Moreover, it's quite probable that your car's ECU automatically limits the upper limit of the rpm in order to prevent further damage to your λ sensors.
  13. Aug 18, 2013 #12


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    Good point. Thanks. I might not have looked as closely as I should have at sparking over.
    Stupid car.
  14. Aug 18, 2013 #13
    Everyone has their ideas, which is helpful, but what I am getting is that there are many possibilities. Ill see if I can take it to a GM dealer and have it looked at.
  15. Aug 18, 2013 #14
    There is no way you can come to that conclusion from the information provided. It's also an expensive part to conclude that its failed. It's one possible failure but not the only one.

    Though as a check, you can give it a few whacks, it'll rattle like buggery if the matrix has disintegrated.
  16. Aug 18, 2013 #15
    Of course I can come to that conclusion based on what he said and my experience although it would be better if he told us about any indication on the dashboard.
    I don't expect anyone to agree or disagree nor I impress my opinion to anyone. I'm just saying my opinion.
    However, as you said, if it rattles I'm right ;)
  17. Aug 18, 2013 #16
    It's just many car forums you'll always come across people that snap to the conclusion that the most expensive possible part has failed. With the symptoms described, it's one of a million things. It's not to dismiss your idea, as it gives another quick free check to do.

    I'm more of the school of eliminating stuff methodically before coming to conclusions of a broken component, especially an expensive one.
  18. Aug 18, 2013 #17

    jim hardy

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    We were just trying to save you a few bucks.
    Many things are simple to fix and the computer, as much as I dislike computers, can pinpoint a lot of troubles.

    Any other symptoms, like a dashboard 'check engine' light?

    I picked up a basic code reader on sale
    it paid for itself in the first week, and again several times since.

    If you plan to keep the car a number of years you might invest in a set of manuals.




    good luck !
  19. Aug 18, 2013 #18
    I appreciate it, I just have little experience fixing cars and I dont want to break anything :/
  20. Aug 18, 2013 #19
    You're absolutely right on that. The description of the problem rang many bells to me because I had the same "symptoms" that's why I said about the catalytic converter. Checking it is quick and easy ;)
  21. Aug 19, 2013 #20
    From the Saturn forums I see that here has been a catalytic converter warranty extension on a number of GM vehicles. That includes the 2008 Saturn Aura with 2.4 L engine and automatic transmission.

    Even if that isn't the OP's problem now it may be later. A power loss of any kind can cause automatic transmission shift points to change.
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