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Thread: Avgas, Mogas, Swift and Mix ratios

  1. #11

    Join Date
    Jul 2018
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    Westfield, IN
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    187

    Default Re: Avgas, Mogas, Swift and Mix ratios

    I am curious about octane related to this. I am an accountant not an expert lol.

    Octane for mogas will decline over time. Bryan at CPS has done a couple of accident investigations recently where "old" gas was determined to be the cause of the accident. I think at least one of these was in TX. He mentioned not running any mogas that had been sitting longer than 30 days. I know of a tank of mogas on a field near me that gets filled about every 6 months. They said "we have never had a problem".

    As I understand, 100LL will maintain its octane. Will Swift?

    Any thoughts on all of this? I guess not a problem if flying all the time, the mogas could never get stale.

  2. #12
    Senior Member Dave S's Avatar
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    Oct 2008
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    St Paul, MN
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    1,833

    Default Re: Avgas, Mogas, Swift and Mix ratios

    Quote Originally Posted by Meyer View Post
    They said "we have never had a problem".
    Precisely the quote of the captain of the Titantic concerning his up to then pristine record as he departed for his date with the iceberg......

    My circle of friends at the 'port who use mogas (as I do) all rely on filling their transfer containers at the gas station the same day they put it in the plane - so they generally park the plane with partial tanks from their previous trip. Although nobody has been able to explain to me exactly how the miracle of "Stabil" works to preserve gasoline, all of them dispense a label recommended amount of Stabil into their transfer containers when they fill them as the fuel will not be burned up entirely when they come back to park the plane after the day's trip.
    Dave S
    Kitfox 7 Trigear (Flying since 2009)
    912ULS Warp Drive

    St Paul, MN

  3. #13
    Senior Member JoeRuscito's Avatar
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    Jun 2018
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    Charleston, SC
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    361

    Default Re: Avgas, Mogas, Swift and Mix ratios

    Swift states their shelf life is about as good as 100ll or about a year.

    So I’m not sure one of my original questions was answered. Is anyone mixing Avgas and Mogas and is there a good way to estimate resulting octane. I am certain the pump gas here is 90aki.

  4. #14

    Join Date
    Dec 2019
    Location
    Washington, DC-ish
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    3

    Default Re: Avgas, Mogas, Swift and Mix ratios

    Calculating octane after mixing fuels is pretty straightforward. Here's a good link that explains it: https://www.sunocoracefuels.com/tech...ulating-octane

  5. #15
    Senior Member
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    Dec 2017
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    Mapleton,UT
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    1,224

    Default Re: Avgas, Mogas, Swift and Mix ratios

    I mix avgas with ethanol 91 and find that running avgas mixed with 91mogas it keeps for long term in my snowmobiles. I run it in a boosted snowmobile and it sits all summer and never have a problem with octane the following year. Doesn’t seem to take much avgas to help stabilize the mogas.

    I am currently running 91 ethanol in my plane.😬 If I where not flying often then I will put a tank of avgas in it.
    Last edited by Shadowrider; 12-07-2019 at 07:50 AM.
    Dustin Dickerson

    Building 7ss STI x 2
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