After Oil Change gas mileage lower?
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Thread: After Oil Change gas mileage lower?

  1. #1
    crv|oc Rank: Member
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    After Oil Change gas mileage lower?

    After the dealer changed the oil and filter, the gas mileage on our 08" awd suddenly is a LOT lower. Do not understand. Use the same gasoline and driving habits haven't changed. Any suggestions why this would happen?

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  3. #2
    crv|oc Rank: Sophomore
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    May be possible that they damaged a O2 sensor - that can drop mileage a lot - or may have knocked the wire off to the sensor. Usually a bad or inoperative sensor will drop fuel mileage. In my manual for 2005 CRV, the first sensor on the Cat convertor in referred to as the Air/Fuel ratio sensor that I would think of as a O2 sensor in a single sensor system. Anyway, this first sensor, since it controls the Air/Fuel mixture, can certainly affect mileage. Complain to the dealer since it is under warranty - suggest the O2 sensor since it is somewhere near the oil filter. At least, this is a place to start.

  4. #3
    crv|oc Rank: Junior
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    Bad O2 sensor should give you a CEL in most cases.

    Overfilling teh crankcase could give you a drop in milege, but I would not expect it to be drmatically lower. Does the engine seem harder to start?

    However, I could see a scenerio where it's grossly overfilled, and oil works its way in large qualtities to the airbox and the IAT and MP sensros get fouled a little.

    Open up the airbox and look under the filter and see it's it's a mess. The crankcase I beleive is vented to the airbox or the intake somewhere.

    I know my motorcycles always are vented to the airbox, but some cars might have it vented to the intake manifold.
    2009 Honda CR-V EX 4WD (Royal Blue)
    2008 Nissan Altima 2.5SL CVT (Silver)
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  5. #4
    crv|oc Rank: Junior
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    Probably put 10-30 oil in it for you! 5-20 is recommended. Hal

  6. #5
    crv|oc Rank: Sophomore
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    those are all really good suggestions. given how cheap an oil change is, if the original guy won't help, take it to another mechanic, let him know the problem, and tell him you really want a good oil change (no overfill, correct weight). almost any mechanic can fill the oil properly and will be particularly attentive since he knows it's causing some issue for you. bet you this solves the issue. check the O2 sensor first but if you have no "check engine" it won't be that ...

  7. #6
    crv|oc Rank: Member
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    After oil change gas mileage lower?

    O2 sensor is good. 5w20 oil was used. Engine air filter ok. Tires all at 30psi as in the past. Used same gasoline as in the past...Still getting 3-4 miles per gallon less than before first oil change. I complained to the dealer and they changed the oil again. Result after one tank of gas, mileage is still lower. Indicator has not moved from 23.6 mpg... I originally was getting 27+mpg. Any other suggestions?

  8. #7
    crv|oc Rank: Silver
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    That is approximately a 14.4% change in fuel economy.

    Are you looking at the MPG display before and after the oil change based on one the immediate tank full or are you letting the miles add up and not reseting every tank full, then reset at the oil change as a way to keep track of the miles on the new oil? If so the average MPG displayed is calculated based on a different set of conditions. Just an idea.

    But that alone should not make a 14.4% difference. Neither will any of the suggestions by themselves make that much of a difference except for the O2 sensor I would think. But you say the O2 sensor is OK.

    The other idea I have is that the gas ethanol ratio was changed by the gas company simultaneous to the oil change by chance. As they do seasonally in some areas. The oil change may not have anything to do with your observation. It might all be attributed to switching from E0 or E5 to E15. That might be responsible for up to maybe 10% reduction. If going from E0 to E15. Maybe??? Going from E0 to E85 willl reduce the economy by almost 25%!

    Talk to your gas station dealer and see if they have changed it recently. If they have either move were they do not use ethanol or learn to live with it as it is.

    -Rg
    Last edited by Radar24; 09-26-2009 at 01:22 PM.

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