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Low octane causing anyone else problems?

Discussion in 'Gen 2 Prius Fuel Economy' started by tomdeimos, Aug 14, 2006.

  1. barbaram

    barbaram Active Member

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    I have been wondering about this. while states are responsible for auditing the accuracy of pumps, who watches the octane ? is it possible for the octane rating to be a bit lower than it should be? would this cause a decrease in mileage?
    In my old cars I would use a tank of the mid gas once in a while.....
     
  2. tomdeimos

    tomdeimos New Member

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    I am now convinced I have had low octane tank fillups causing most of my fuel related low mpg tanks. But it has not happened again.

    I have been experimenting with octane grades and watching the canview and the effects are very visible.
    Normal cruise is not showing any noticable difference with fuel and spark advance tends to stay at 29 to 32 degrees.

    With acceleration I estimate at say 40 mph and warmed up I can accelerate with up to 60% throttle with an 87 octane tank, before the knock sensor retards. With 89 octane it goes to more like 75% before this happens.

    When the sensor triggers it retards drastically going from maybe 38 to 42 deg advance down to 27 degrees. Once this happens it stays retarded till you stop accelerating and then resume more gently.

    Seems like regular 87 octane is OK for high mpg drivers but not for agressive drivers. If a tank is just a little lower than spec like 85 octane, it would have a noticable impact on most drivers mpg.

    MPG impact of octane would be more important in city driving and in mountains than normal highway driving.

    My experiments here were all with Shell gasoline. I've used a couple of tanks of 93 octane too with no problems or mpg drop, but that was before I started watching the spark advance readouts.

    I'm going back to regular now, but will put in premium with a partial fill up anytime I see the spark retard happening more than normal.

    I was going to try to compare mpg too this time, between the 87 and 89 octane, but our early swtch to winter fuel killed that idea. My mpg is down close to 5 mpg now in my regular commuting. I wll get much of this back after this weekend, as I will winterize and start using my block heater for the winter.
     
  3. DaveinOlyWA

    DaveinOlyWA 3rd Time was Solariffic!!

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    sorry, cant believe your statement. is it a coincidence that MA is one of the states with stricter air polution guidelines and PA is not??

    i think not. there has been a million studies over the impact of high octane gas in a car that does not require it and there has never been any evidence shown that disputes the statement that you are wasting your money by buying it.

    but that is ok. keep reporting back. any final conclusion made with the amount of data you have might be a bit premature. in time, i think your high octane MA gas will perform just as your low octane MA gas does.

    for me, i can drive to Idaho and get better performing gas (actually i went to Montana but if i didnt feel like driving as far). i too averaged 56 mpg on a trip averaging about 70 mph coming home. same trip going out with WA gas ....51.5 see a corellation here??
     
  4. tomdeimos

    tomdeimos New Member

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    <div class='quotetop'>QUOTE(DaveinOlyWA @ Oct 20 2006, 11:19 AM) [snapback]335556[/snapback]</div>
    Not sure what you don't believe.

    1 I do get great regular gas in MA most of the time, and that is what I normally use.
    2 Premium bought in MA works great too. So due to both of these, the issue is not PA vs MA fuel I think.
    3 CAN VIEW clearly shows when the octane is not enough. If it retards the spark for normal acceleration that is inadequate octane by definition.
    4 I now check the spark advance on every tank, but I have not had another problem tank since, and no unexplained low mpg tanks either since my trip.
     
  5. dmckinstry

    dmckinstry New Member

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    <div class='quotetop'>QUOTE(DaveinOlyWA @ Oct 20 2006, 08:19 AM) [snapback]335556[/snapback]</div>
    Yes, I do. I believe it's due to elevation change. I get lower mileage traveling from Olympia to Spokane than I do from Spokane to Olympia as well. My mileage goes up dramatically after reaching Snoqualmie summit heading west. By the time I get to Olympia I've more than made up the drop in mileage lost between Spokane and Snoqualmie.

    Dave M.
     
  6. Pinto Girl

    Pinto Girl New Member

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    <div class='quotetop'>QUOTE(Tempus @ Aug 14 2006, 02:33 PM) [snapback]303149[/snapback]</div>
    I think you put this very well.

    I've also read that actually, high octane fuel burns less well than regular.

    The idea with premium (higher octane) fuels is that they permit higher compression without preignition; the octane is actually keeping the fuel from burning, not providing additional energy.

    The level of oxygenation or other variations in the fuel blend is probably at the root of what you're experiencing.
     
  7. tripp

    tripp Which it's a 'ybrid, ain't it?

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    I'm probably using lower octane than most folks in the states. Here in Denver "regular" gasoline is 85 octane. That's what I use and I've had no problems nor noticed any pronounced drop in MPG.
     
  8. tomdeimos

    tomdeimos New Member

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    You folks are all stating correct info but still neglecting my main points.

    1 Octane that is too low causes the spark advance to retard and stay retarded for some time.
    This drastically cuts mpg and dwarfs any energy differences.

    2 I happily burn regular fuel most of the time. All I am saying is when I buy regular it is not always up to the specs for regular. I believe that is the primary cause of my tanks that have had unexplained low mpg. The other cause would be differing amounts of ethanol and or water in the fuel.

    3 The can view works very well to detect any octane issues if and when they occur.
     
  9. dmckinstry

    dmckinstry New Member

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    <div class='quotetop'>QUOTE(tripp @ Oct 20 2006, 03:45 PM) [snapback]335872[/snapback]</div>

    But of course, 85 octane is the correct rating for higher altitudes. It does for you in Denver what 87 does at sea level.

    Dave M.
     
  10. jroth74

    jroth74 New Member

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    Here is something to think about when deciding what brand of gas to buy. We drive hybrids and get the best mileage available, no matter what brand we buy. The incentive for me is where does the oil come from. Further more, not contributing money to terrorist and the oil tycoons (Bush) who are causing hell on earth in the Middle East is the #1 reason I bought a Prius. There is a lot of mixed info on who really sells Middle East oil, but some companies have proven not to. Do the world another favor (1st one is driving a Prius) and find out where you can buy Satan free gas in your area.

    http://urbanlegends.about.com/library/bl-boycott-oil.htm
     
  11. kdailey356

    kdailey356 New Member

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    I use premium in all my other cars, but heard it would give the prius problems? Is it okay for me to use 93?
     
  12. F8L

    F8L Protecting Habitat & AG Lands

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    I agree that if the car is going into a knock retard condition then your milage will be hurt depending on the severity of the timing reduction and the decay time for the timing to come back. Sounds like I might have to get Can-View. Might have helped me to firgure out the wierd mpg loss I suffered a few months ago.
     
  13. Schmika

    Schmika New Member

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    <div class='quotetop'>QUOTE(CapeCodPrius @ Dec 4 2006, 10:30 PM) [snapback]357707[/snapback]</div>

    Did you not read all the posts. Toyota tech manuals suggest not using 93. Anecdotal evidence about better MPG seems to be unclear or downright refuted.
     
  14. Kurtiosity

    Kurtiosity New Member

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    I see that this is an old discussion. But here I am piping up anyway. java script:emoticon(':rolleyes:',%20'smid_12') The thought that comes to mind is what octane is the gas. Here in Oregon, regular is 87 octane. In Nevada, regular is 85 octane. And as an aside, I don't buy ARCO gas at all. We have an old Subaru that requires Premimum. When I use ARCO gas the car would knock badly. Any other brand, no knock.
     
  15. MtBiker

    MtBiker Junior Member

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    <div class='quotetop'>QUOTE(dmckinstry @ Oct 22 2006, 07:01 AM) [snapback]336356[/snapback]</div>


    Is there a general consensus as to what is the minimum altitude in order to be considered a "higher altitude" and thus a candidate for using 85 octane?
     
  16. dmckinstry

    dmckinstry New Member

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    <div class='quotetop'>QUOTE(MtBiker @ Jan 8 2007, 03:30 PM) [snapback]372745[/snapback]</div>
    I don't know exactly, but when you get into Montana, it's usually 85 octane. In areas where it's only 2500 ft. elevation the gas is normally 87 octane. I'm guessing between 4,000 and 5,000 ft is where the change is made.
    We need a response from those that drive at the "edge" of where they change the octane to 85.


    Dave M.
     
  17. MtBiker

    MtBiker Junior Member

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    <div class='quotetop'>QUOTE(dmckinstry @ Jan 8 2007, 04:54 PM) [snapback]372762[/snapback]</div>


    I'm in Salt Lake City (EL 4300') and 87/88 appears to be the standard octane although 85 is always a choice at the pump as well. We bought our Prius in Rexburg, ID (EL 4865') and the salesman said they filled it up with 85 because it's the standard octane for their elevation. We've been using 85 this winter and have had no indication of knocking and our mileage is about 48 with snow tires on. We'll be listening close for pinging as the weather warms up though and will change to 87 at the first sign of detonation.