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does overfull oil effect MPG--Yes

Discussion in 'Gen 2 Prius Fuel Economy' started by Stevep, Feb 6, 2006.

  1. Stevep

    Stevep Junior Member

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    I have read several posts here that say that if the oil is over full, it will lower the MPG. I can say that from my recent experience, this is true.

    I just got my first oil change at the dealer a few days ago. I had about 1/2 a tank of gas, and was getting about 53 MPG driving the same as I would any other car. After the oil change, my MPG dropped from 53 to 49. :( I just checked the oil level, and despite telling the dealer not to overfill, :angry: the oil level is about 1/2 inch over the full line. I have driven about 150 miles since the oil change.

    When I get home tonight, I will drain the oil, install one of those valves, and refill the oil to about 1/2 way between the two marks.

    From now on, I will change my own oil. That way I will know it is right.

    Some ancent sage said it best. " if you want it done right, do it yourself". Sure applies in this case.
     
    #1 Stevep, Feb 6, 2006
  2. galaxee

    galaxee mostly benevolent

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    did they rotate your tires?

    since it would be your first tire rotation, that would affect mpg too.
     
    #2 galaxee, Feb 6, 2006
  3. Bob Allen

    Bob Allen Captainbaba

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    Can someone explain how an oil overfill affects mileage?
     
    #3 Bob Allen, Feb 6, 2006
  4. Stevep

    Stevep Junior Member

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    Not real sure, but my logic favors the opinion that increased oil in the engine will cause increased pressure, therby causing the engine to work harder to overcome the increased oil pressure. I know that if you have a large amount of extra oil in a convential engine, the pressure can cause seals to get blowo out. I would think the ICE would work the same way.
     
    #4 Stevep, Feb 8, 2006
  5. Vagabond

    Vagabond Active Member

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    This is correct - overfill causes the crank to drag on the excess oil in the pan and slow down, and can cause the engine-damaging frothing in the pan as well.

    Honestly the manufacture's specs are not allways correct anyway, for instance in my SVT Contour I have to put an additional 1/2 to 3/4 of a quart then what they say you should put in. I'm guessing SVT didn't account for the oil cooler added to the car when they published their dealer's guide.
     
    #5 Vagabond, Feb 11, 2006
  6. rogerSC

    rogerSC Member

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    When I took delivery of my car the oil was over filled. I didn't check it until I was already home, so I got some "equipment" and removed the excess (about 3/4" on the dipstick). A pain in the neck, and I didn't notice any difference in gas mileage, but I felt better about it.

    I went to the same dealer about 3 weeks ago for my 6 months tuneup, and asked that they check the oil level after the refill, since I had heard that over-filling was a problem. The guy kind of looked at me like I was retarded, and assured me that they do that as a matter of course. I didn't mention that when I picked the car up from them new, that it was over-filled. However, when I checked the oil level after I got home, I was happy to see that it was spot-on. Maybe making the mechanics conscious of the fact that you care about over-filling is helpful.

    -Roger
     
    #6 rogerSC, Feb 11, 2006
    Sam Brinson likes this.
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