88 octane - loss of MPG

Discussion in 'Gen 3 Prius Main Forum' started by Steelerfan2018, Jul 16, 2021.

  1. Steelerfan2018

    Steelerfan2018 Junior Member

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    Hi all,
    I have a 2011 that I have owned since May. I regularly get around 42-43mpg, even with the AC running.

    A short time ago I was at a Sheetz and saw 88 octane fuel at a lower price - I thought 88 octane was just like regular fuel, with +1 octane.

    Anyways I filled the tank and noticed that no matter how well I drove, I always hovered around 36mpg. Even using EV mode etc. This has gone on for about a week, with me thinking that it has been so hot that the AC is probably working more.

    I looked up the 88 octane out of curiosity and there are posts out there of people losing MPG using this stuff. So my Q - is this an issue or is there something wrong with my car? I put in a half a tank of normal 87 hoping to dilute the 88 but haven't driven enough to see if it has improved. Is there anything I should be doing?

    Any thoughts on this greatly appreciated,
    Rob
     
  2. SkywalkerPhD

    SkywalkerPhD New Member

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    88 has 5% more ethanol which makes it a less efficient fuel. That probably accounts for a some of the mpg loss, but not all.


    iPhone ?
     
  3. bisco

    bisco cookie crumbler

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    i have never heard of higher octane being a problem, just no benefit. it can't hurt your car, it probably is the a/c use.
     
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  4. mmmodem

    mmmodem Senior Taste Tester

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    88 octane fuel is according to this article also E15 fuel. In other words, 15% is ethanol. Regular 87 octane is E10 or 10% ethanol in most places. Ethanol has less energy than gasoline, therefore, 88 Octane fuel just like E85 fuel nets you lower mpg than regular gasoline.

    Q & A: What's up with that 88 octane fuel? | Business | gazettextra.com

    I probably wouldn't use it unless I was desperate or my car was rated to run E85. People have done the math on cheaper E85. It works about even for the savings in cost vs lower mpg. I'm guessing the same math will work for 88 Octane except our the Prius isn't rated to run above E10 fuel as far as I know.
     
    #4 mmmodem, Jul 16, 2021
    Last edited: Jul 16, 2021
  5. sam spade 2

    sam spade 2 Senior Member

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    Yes I bet it accounts for ALL of it.
    AND his car probably is not approved to use E15 anyway.
     
  6. ColoradoBoo

    ColoradoBoo Junior Member

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    Yep, E15 ("Ethanol 15%") is the most ethanol Prius' are supposed to run on. Mileage is horrible with ethanol, anyway, it burns very hot and can hurt modern engines. "Flex Fuel" engines, like my Tundra, can take up to E85 but I won't ever use anything more than E10 (which most pumps, unfortunately, have these days due to Federal rules.)
    Top Tier gas is the best for our Toyota cars. Do a search on Google and find out where your nearest one is and ONLY get fuel from them...never go cheap with gas, folks. (Only takes one tank of bad gas to do a lot of engine damage.) I believe most Costco's have Top Tier gas. For me, my local 7-11 with Conaco gas is Top Tier. To clean out our fuel system (injectors, EGR, etc.) run a tank of high-test from a Top Tier and the cleaners will do a great job. (Run it a few times a year.) My favorite gas station was our truck stop in the interstate but I found out they don't have Top Tier gas so don't use them even though they are usually a nickle or so cheaper than 7-11....not worth the risk.
     
  7. Steelerfan2018

    Steelerfan2018 Junior Member

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    Hi all - thanks for the comments.

    In the past, I would take my normal daily trip (I take this trip 7 days a week) - roughly 30 mins to the destination, spend and hour, then 30 minutes back. Before I put in the 88 octane, I would typically get in the low 40s - say 42mpg. That is with AC running and normal "Prius" driving.

    When I was using the 88 mpg dipped even though I pulled out every trick I knew - I had the ECO button on, and when stuck in traffic used the EV. Used the EV a lot. Going down hills I used the B gear etc. Aggressively trying to get high MPG, I still got 36 mpg tops.

    Today (with half the tank 88, half normal 87) I took my normal morning trip - just normal driving and I hit 39 mpg. I haven't hit 39mpg in almost two weeks since I started using the 88 octane.

    From this I blame the ethanol.

    Thoughts?
    Rob
     
  8. sam spade 2

    sam spade 2 Senior Member

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    Is that NOT what everybody has been telling you so far ???
     
  9. sam spade 2

    sam spade 2 Senior Member

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    Where exactly did you get that MIS-information about ethanol burning hotter.....enough so to damage engines ??

    AND you have been brainwashed by the "Top Tier" marketing hype.
    Depending on exactly where you live, there might be ZERO difference between the gas at a Top Tier station and the no-name discounter down the road. Because it all comes from the same tank farm, via the same pipeline, from the same refinery.
     
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  10. Grit

    Grit Senior Member

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    Arco is always priced lower than chevron and shell, how is cheap arco on the top tier lists then?
     
  11. privilege

    privilege Member

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    87 octane = the best for normally aspirated non high compression engines
    89 octane = similar but at higher cost and no benefits
    93 octane = similar but at even high cost with no benefits
    105 octane = ditto 93
    110 octane = see a pattern yet ?

    ETHANOL added to any of the above = decreased fuel economy, plus you're paying for corn subsidies

    ethanol 15/30/45/100% = incredibly bad fuel economy, plus you're paying for corn subsidies, and you have a really good chance of hurting your fuel system

    corn sucks. burn real gas, the lowest octane you can find (87 should be the lowest) for the best fuel economy
     
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  12. black_jmyntrn

    black_jmyntrn Member

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    I don't know about all if you but when I use 91 here in California I get better MPG.
     
  13. Rmay635703

    Rmay635703 Senior Member

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    Meh, depends on outside conditions and your car

    My Volt runs about 10% better FE than RUG in 80F+ weather on 88e15
    (based on 7 years data)
    I also have half the “knock” readings per the tuner software on it.
    Also E15 locally has always been 20-40 cents a gallon cheaper than rug which more than makes up for the 2% loss of energy content.

    When temperatures top 100F and it is muggy/rainy I loose about 10%+ regardless of my fuel choice

    A few low MPG tanks mean absolutely nothing
    Correlation is not causation and a few experiences do not prove a trend and it takes years of data to show a true trend.

    I would lean toward your economy change being more related to weather, traffic/driving speed conditions, wind, rain, tire inflation, oil type, tire changes, bad gas, water in the gas, etc before I would consider the 2% energy content change.

    Could e15 give you lower Fe, certainly but I doubt a 2% difference is measurable to you.
    I would alternate fuel types if e15 is cheaper and see if it gives the same result every time,

    If I doesn’t something else may have changed , even mechanical, e15 has also been known to sop up water from a bad head gasket and can be a tell if you have a failure starting
     
  14. Pulse07

    Pulse07 Member

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    Running high test gas (I assume you mean 91 or 93) have zero benefits on a Prius. To be certified Top Tier gas, the station have to have Top Tier detergents in all the grades it sells. Some stations like Shell advertise their "V Power" gas has 7x the detergents compared to federal standards. But to be Top Tier, Shell also have to sell Top Tier detergent in their regular gas.


    Probably their business approach. Selling volume over mark ups. Less advertising etc.


    Most places are 10% Ethanol. Ethanol is used an octane booster , Octane rating of E100 is about 100, Blending lower refined gas like 85 and then blending it with 10% ethanol makes it 87.
     
  15. Grit

    Grit Senior Member

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    :sleep:
     
    #15 Grit, Jul 17, 2021
    Last edited: Jul 17, 2021
  16. Rmay635703

    Rmay635703 Senior Member

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    The op lost 15-18% of his fuel economy because of a fuel with 2% less energy per gallon .

    If all else is the same
    Either his car has problems or the fuel had water in it.

    This is similar to the e10 gets half the fuel economy comments I used to see 10 years ago, no merit or leaving something out.

    Neither my Volt, Insight or Cobalt seemed to get statically significant reductions in economy going to e15, Winter is about the only time I’ve noted a drop in 88e15 economy but it is within the margin of error.
     
  17. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    Pay attention to weather. Air conditioner usage can impact your MPG by a fair amount, and because these cars have thermostatic control of the AC, you aren't always aware of how much you are using.

    As noted above, the E15 fuel has less energy per gallon so you are guaranteed to take an MPG hit by using it, but it should not be as big as what you've reported.

    It is possible (probable, in my mind) that air conditioner usage explains the rest, but it will be difficult to prove either way.
     
  18. Pulse07

    Pulse07 Member

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    It's in your head. There's no advantage using 91/93 on a car designed for 87. All gasoline grades contain the same amount of chemical energy.
     
  19. Grit

    Grit Senior Member

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    when I go SF, I drive up long hills. When I get to a certain gas station at the top of the hill, I tend to get the best mpg from that arco compared to the shells and chevrons at home. That arco gas station has the best gas.
     
  20. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    If the 91 also has less ethanol than the regular grade, then this is possible.

    To say it another way- the anti-knock index (octane rating) does not affect MPG, but the ethanol content does.

    Many pumps are tagged with "Up to 10% ethanol" and you never get any further details.

    So if the AKI91 is 3% ethanol and the AKI87 is 10% ethanol then yes... you will get slightly better MPG out of the AKI91.... but it has nothing to do with the AKI/octane rating.
     
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