My mileage went from 39 to 45? 2007 prius

Discussion in 'Gen 2 Prius Fuel Economy' started by JacksonMs, Oct 3, 2009.

  1. JacksonMs

    JacksonMs Junior Member

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    I have a 2007 prius touring... I drive about 100 miles highway round trip to work daily...
    generally, my MPG is around 39 highway. The other day, I accidently filled up with premium unleaded instead of regular... My MPG increased to 45 with no change in the way I drive...
    Has anyone else noticed a change in MPG based on what grade fuel they use?

    Thanks!
     
  2. Sandy

    Sandy Hippi Chick

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    hi i get 45-50 on regular
     
  3. Omni-TaG

    Omni-TaG New Member

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    I tried both premium and regular... i'm not shure but i think that stops and starts of gas engine are smoother with premium grade.
    Then i saw non diferences in gas mileage.
     
  4. Gadgetdad

    Gadgetdad New Member

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    This has been discussed before on PC. Most likely the difference is less air conditioning use now that fall has come. Short trips, cold weather, heater or A/C use, low tire pressure and aggressive driving accounts for low MPG's.

    Premium gas in the Prius is just wasting $.
     
  5. Ophbalance

    Ophbalance Member

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    Isn't premium supposed to be ethonal free? That might account for a gain of 3-10%, provided your regular gas has E10 in it.
     
  6. Gadgetdad

    Gadgetdad New Member

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    Good point if the regular gas is watered down with Ethanol and the premium isn't. Out west here the same thing happens when the mandated winter gas is used with oxidizers (MBTE), you have to use more fuel to go the same distance. Handy for tax revenue for the State that requires it under environmental pretenses!
     
  7. uart

    uart Senior Member

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    Here in Australia we generally get a choice of three grades:

    - "E10" containing 10% ethanol.
    - "Regular" (sometimes just called unleaded, though they are of course all unleaded)
    - "Premium" (various types of premium from the different brands, with various higher octane ratings).

    E10 is the cheapest here, though typically only 1.5% to 2.5% cheaper than regular grade. Premium grades however are usually significantly more costly, typically around 10% to 14% more than regular.

    I haven't made any systematic tests of Regular versus E10, though in tests that I've read they usually find slightly lower mileage with the E10, at least enough to nullify any benefit from it's cheaper price.

    I did test one full tank of premium grade on the Prius just to see if it made any difference. The result was that the difference (if it existed at all) was very small, no more than about 2% (which could even have been natural variability). It certainly didn't justify it's 12% price premium.
     
  8. Frayadjacent

    Frayadjacent Resident Conservative

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    Ethanol content is probably the culprit.

    Higher octane gas is not about efficiency or power. It's about compression ignition (detonation) and avoiding it.

    Using higher octane gas in a car that doesn't need it gets you nothing, all else being equal.

    If you were stuck using E10 regular, and found some regular with no ethanol in it, you'd get better economy with the non ethanol regular.
     
  9. philobeddoe

    philobeddoe ΜΟΛΩΝ ΛΑΒΕ

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    nice avatar ... and i'm a fan of Ayn Rand as well :thumb:


    i've run the three available octane grades here in SoCal with no difference in mileage whatsoever

    i'm not sure of the compression ratio of the Prius four banger, but i'm guessing it ain't 11:1

    87 should do the trick :thumb:

    something else is accounting for your increased mileage
     
  10. bac

    bac Active Member

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    Holy cow! How do you manage 39mpg? Do you drive in the triple digits, or with the emergency brake on? :eek:

    -Brad
     
  11. spitinuri

    spitinuri Member

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    Ethanol content or the lack thereof is the culprit. In Missouri the law states that all grades must have 10% Ethanol. The only exception is for boat fuel (seem they found that Ethanol damages boat motors). I'm averaging 48-52 mpg now that it is getting cooler. I would love to have the extra 5 mpg.
     
  12. The_Gunrunner

    The_Gunrunner New Member

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    Gadget Dad is right. A lot of things that can influence the way your Prius uses fuel. It's fall right now so more than likely you're not using the air conditioner or heater very much, if at all. Second, octane is a chemical compound added to fuel to regulate the rate of burn. Only higher compression engines in sports cars require premium fuel. It won't hurt your Prius, but it certainly won't help. You just wasting money with premium. However, it does help out a lot to use Plus-rated fuel (usually 89-90 octane) when you're using the air conditioner. It will reduce engine "knocking" (pre-ignition) during the summer months.
     
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