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  1. #1
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    Subaru can has 85 octane gas?

    So the dealer and the user manual sez I need to use 87 octane for my new non-turbo Subaru. Minimum octane here in CO is 85. I have heard that the altitude here makes 85 behave the same as 87 at sea level. Bullcrap? Do I really need to use mid-grade fuel here at 6k feet or would that just be wasting money?
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  2. #2
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    85 is fine at altitude.

  3. #3
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    i know that it makes a huge difference in my wrx when i run cheap gas. i dont think it should matter on the non-turbo cars.

    on a similar note, i've heard you can run cheap gas on long road trips?
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  4. #4
    It's not TOO Cold!
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    There is probably a disclaimer in there somewhere, but here you can use 85. When you drive to Portland for next year's Subbie Fest, the lowest octane they will have is 87.
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  5. #5
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    Q:
    I live in Arizona and use 87-octane regular. In Utah, Idaho and Nevada, stations were selling 85-octane as regular gas. This forced me to pay more for midgrade 87-octane. Is this the latest petroleum-industry scam to get more of our money? Will my car run okay on this bogus 85-octane regular?

    A:
    Octane is the ability of a fuel to resist knock, and high-compression engines tend to knock more. The obverse of that is that lower-compression engines can run on lower-octane gas. Air is thinner the higher above sea level you go. Less air going into the cylinders means less pressure at top dead center when things go bang. It's a lot like lowering the compression ratio in the engine, reducing the need for high octane. Cars will run just fine on lower-octane fuel when they're well above sea level--and all of those states are. Hopefully, by the time you get back down to denser air, you've burned off most of the low-octane stuff, and can refill the tank with higher-grade fuel.

    30 Car Mysteries Solved: Low Octane Fuel at High Altitudes - Popular Mechanics
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  6. #6
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    I know this threw me when I visited Colorado years ago, but I think QQQ's post above addresses the situation pretty well. I know for a fact my H.O. Quad 4 (that gives you an idea how long ago it was) was producing no where near it's rated output climbing those mountains!
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    Quote Originally Posted by QuiQuaeQuod View Post
    Q:
    I live in Arizona and use 87-octane regular. In Utah, Idaho and Nevada, stations were selling 85-octane as regular gas. This forced me to pay more for midgrade 87-octane. Is this the latest petroleum-industry scam to get more of our money? Will my car run okay on this bogus 85-octane regular?

    A:
    Octane is the ability of a fuel to resist knock, and high-compression engines tend to knock more. The obverse of that is that lower-compression engines can run on lower-octane gas. Air is thinner the higher above sea level you go. Less air going into the cylinders means less pressure at top dead center when things go bang. It's a lot like lowering the compression ratio in the engine, reducing the need for high octane. Cars will run just fine on lower-octane fuel when they're well above sea level--and all of those states are. Hopefully, by the time you get back down to denser air, you've burned off most of the low-octane stuff, and can refill the tank with higher-grade fuel.

    30 Car Mysteries Solved: Low Octane Fuel at High Altitudes - Popular Mechanics
    Nice link! Cool read.
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  8. #8
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    The altitude is the key. It will run fine on 85, just as others have said.

  9. #9
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    Above 10,000 feet, you can run the Subie on Diesel.
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  10. #10
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    Yep, 85 works here in CO. That was one selling point for me, not having to run higher octane gas. Did you get the 4cyl or 6?
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  11. #11
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    there's a tremendous amount of mis-info concerning octane ratings...

    most people think higher octane fuel is more 'explosive'...nope. a gallon of gasoline contains the same amount of potential energy, regardless of octane.

    as previously posted, octane is used to retard the rate of flame travel in high compression engines. if your engine runs smoothly on a given octane, there's zero reason to buy a higher octane.

    my dad used to think he was giving the engine a 'treat' when he filled up with high-test.
    eff all y'all...

  12. #12
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    I was curious so I found a link for you.

    popularmechanics.com/cars/how-to/repair-questions/4345737

  13. #13
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    There is 85 octane there? We have 87, 91 and 93 here in FL. I use 87 as they manual says. Running higher octane gas than the engine needs in a complete WASTE.

    From wikipedia:

    In the US octane rating is displayed in AKI. In the Rocky Mountain (high elevation) states, 85 AKI (90 RON) is the minimum octane, and 91 AKI (95 RON) is the maximum octane available in fuel[citation needed]. The reason for this is that in higher-elevation areas, a typical naturally aspirated engine draws in less air mass per cycle because of the reduced density of the atmosphere. This directly translates to less fuel and reduced absolute compression in the cylinder, therefore deterring knock. It is safe to fill a carbureted car that normally takes 87 AKI fuel at sea level with 85 AKI fuel in the mountains, but at sea level the fuel may cause damage to the engine.

    A disadvantage to this strategy is that most turbocharged vehicles are unable to produce full power, even when using the "premium" 91 AKI fuel. In some east coast states, up to 94 AKI (98 RON) is available.[23] In Colorado as well as parts of the Midwest (primarily Minnesota, Iowa, Illinois and Missouri) ethanol-based E-85 fuel with 105 AKI is available.[24] Often, filling stations near US racing tracks will offer higher octane levels such as 100 AKI[citation needed]. California and Florida fuel stations will offer 87, 89, and 91 AKI (91, 93 and 95 RON) octane fuels, and at some stations, 100 AKI or higher octane, sold as racing fuel.
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  14. #14
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    Quote Originally Posted by Bulldozer View Post
    Yep, 85 works here in CO. That was one selling point for me, not having to run higher octane gas. Did you get the 4cyl or 6?
    4cyl---

    here's what the salesman said when I asked him about it:

    I asked our technician that’s been working on Subarus over 20 years. He tells me that the cars will run smoother with 87 and over a long period of time, the 85 wears things like your emissions systems faster. I personally use 87 in my vehicles and I feel that they run better and give just a little better fuel economy- but that’s up to you.


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  15. #15
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    This is great to know. Next time we drive up to the mountains I'll pull over, drain our gas, and refill it with lower octane. Unless it's cold out, which case I'll have my wife do it.
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  16. #16
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    I have never seen 85 sold before. I have always lived on coasts, though.

  17. #17
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    Quote Originally Posted by QuiQuaeQuod View Post
    Cars will run just fine on lower-octane fuel when they're ... above sea level--
    It's when you try and run a car below sea level that you run into problems....


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    Its a little hard to believe 85 at that altitude would be any problem at all. The air-to-fuel ratio is lower; should help retard the combustion or explosiveness (not the same thing as energy content; fuel oil has more Btu/gallon) of the lower octane fuel.

    Plus with them fancy computers on the car controlling stuff; no problem.

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    Quote Originally Posted by Oxtox View Post
    there's a tremendous amount of mis-info concerning octane ratings...

    most people think higher octane fuel is more 'explosive'...nope. a gallon of gasoline contains the same amount of potential energy, regardless of octane.

    as previously posted, octane is used to retard the rate of flame travel in high compression engines. if your engine runs smoothly on a given octane, there's zero reason to buy a higher octane.

    my dad used to think he was giving the engine a 'treat' when he filled up with high-test.
    Octane rating is simply a measure of how compressable a fuel is before it self-ignites. Gasoline is compared to octane, and diesel is compared to cetane. The number is what percent of octane's compression the gasoline achieves. You are correct, it has nothing to do with temperature of combustion, or energy content.

  20. #20
    It's not TOO Cold!
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    [QUOTE=Bocephus Jones II;3738444]4cyl---

    here's what the salesman said when I asked him about it:


    What a load of BULL
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    How bocepherous!

  22. #22
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    Just be sure you don't mix the old gas with the new gas.

  23. #23
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    Quote Originally Posted by MoonHowl View Post
    Its a little hard to believe 85 at that altitude would be any problem at all. The air-to-fuel ratio is lower; should help retard the combustion or explosiveness (not the same thing as energy content; fuel oil has more Btu/gallon) of the lower octane fuel.

    Plus with them fancy computers on the car controlling stuff; no problem.
    This very true Except I believe in the Winter months the ethanol (corn subsidy) additive they use for "pollution" control hampers the detonation and makes cars a "little" sluggish. An octane additive could be used if you want to experiment with car performance. It would be hard to tell if performance improved but you could track mileages.

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    The only problem with ethanol at altitude is it binds with water and forms relatively large droplets. When those droplets go through the injectors they can cause a miss. A fuel additive can help with the water.

    Ethanol, and other "oxygenated" fuel additives are pre-burned, so you just have part of your fuel going along for the ride, and not really doing anything in the combustion process. Otherwise, the extra oxygen does nothing.

  25. #25
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    FWIW, I live at altitude and run my Ducati on 85 all the time with no problems. The manual calls for 95-98 RON which would be 91-94 on the US scale.
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