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Thread: which fuel grade - 93 or 89 or 87?

  1. #1
    Join Date
    Jun 2005
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    Default which fuel grade - 93 or 89 or 87?

    I'm wondering which fuel grade I should use for my 2004 XC70. I know that according to the manual, 91 or higher octane is recommended and the minimum required is 87. I've been mostly using 89 for the last two year (since I bought it), and I think it has been fine. I'm thinking about switching it to 87 and am wondering if it can do any harm. Does anyone know about this?
    Last edited by sunshine; 06-16-2005 at 09:04 AM.

  2. #2
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    Dec 2004
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    Waterloo, Canada
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    Default

    I would go with the highest octane rating you can afford.I put nothing but either 91 or 94 octane. In fact the difference in price between 91 and 94 is sometimes 1-2 cents per litre. In the grand scheme of things what would you save each year by using 87 octane? Not more than perhaps $150 and you would get a car that should perform and run better. Regards

  3. #3
    Join Date
    Mar 2004
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    Colorado, USA
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    Default re octane

    Discussions over which octane to buy are like those over oil change
    intervals - lots of strong opinions, not much statistically-valid evidence,
    in the end it may not matter all that much!

    That said, my opinion is that you should run the lowest octane that
    the car seems happy with. Higher octane is not necessarily "better" -
    octane is simply a measure of resistance to knock. Higher octane
    means fuel ignites less easily. For high-compression engines, this is
    important, but less so for engines like the Volvo 5 cylinder. Oil companies
    market higher octane fuels as somehow better for your car, but that's because their profit margins are much higher on those fuels.

  4. #4
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    Oct 2003
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    Anything greater than 91 octane is very likely a waste of money, as 91 is what the engine is designed to run optimally on.

    If you alternate fill ups between 93 octane and 89 octane, the blend you achieve in the tank will average out at 91. i.e., Fill your tank with 93 octane, when it gets down to about 1/2 refill with 89, run it down to 1/2 and fill with 93, etc., etc. This strategy would get you the optimal performance for the least amount of money.

    Personally I use 89 octane nearly all the time. I only blend in some 93 when the weather is very hot, which is when the engine is most susceptible to "knock", and most likely to suffer reduced performance as the engine managment system dials back the ignition timing to prevent the knock. This is when having higher octane fuel is most helpful.
    '04 XC70, Ash Gold / Taupe, Premium, Touring, Tinted Rear Glass, Rear Skyddsplåt, Wing Profile Load Bars, USA Spec 11,
    StonGard Light Protection, Yokohama YK 580s, MevOtech Sway Bar Links, ipd HD TCV, subframe & top brace poly bushing inserts.

  5. #5
    Join Date
    Oct 2003
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    Michigan, USA
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    Default

    Quote Originally Posted by Phrog
    Higher octane
    means fuel ignites less easily. For high-compression engines, this is
    important, but less so for engines like the Volvo 5 cylinder.
    Semi-true. A turbocharged engine like the Volvo T5, is a "high compression" engine, as the turbo charger raises the effective compression ratio.
    '04 XC70, Ash Gold / Taupe, Premium, Touring, Tinted Rear Glass, Rear Skyddsplåt, Wing Profile Load Bars, USA Spec 11,
    StonGard Light Protection, Yokohama YK 580s, MevOtech Sway Bar Links, ipd HD TCV, subframe & top brace poly bushing inserts.

  6. #6
    Join Date
    Mar 2004
    Location
    Colorado, USA
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    104

    Default Re octane and turbo

    Good point re the turbo. However with an intercooler (which I think the
    XC70 has), air temp is reduced. It's high air temperature, not pressure or
    compression, that in the end causes knock (premature ignition).

    Interestingly, here in Colorado we're at ~6000 feet and thus use lower
    octane fuels. PV=nRT...less P means lower T, all else equal.

    Any more engineers want to jump in here?

  7. #7
    Join Date
    Jan 2005
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    Colorado Springs
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    Default

    Quote Originally Posted by Phrog
    Good point re the turbo. However with an intercooler (which I think the
    XC70 has), air temp is reduced. It's high air temperature, not pressure or
    compression, that in the end causes knock (premature ignition).

    Interestingly, here in Colorado we're at ~6000 feet and thus use lower
    octane fuels. PV=nRT...less P means lower T, all else equal.

    Any more engineers want to jump in here?
    I also live in Colorado (Colorado Springs). When my car was delivered to me by the salesman, one of the things he had told me was that I should use a lower octane during the winter season. Can you or anyone on this thread tell me whether I should indeed take his advise or simply stick to the same octane regardless of the season? Thanks in advance.
    '05 XC70 Crystal Green - DSTC - 6CD Changer - Rear Park Assist - Third Row - Integrated Booster - Nokian WR - Thule Evolution 1600 on Wing Profile. Photos of XC70: http://sys-2005volvoxc70.blogspot.com/ Travel Photos: http://my-traveling-photolog.blogspot.com/

  8. #8
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    Mar 2004
    Location
    Colorado, USA
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    104

    Default re: winter octane

    There are two effects here: winter means lower air temperatures means
    (all else equal) lower in-cylinder temperatures means less chance
    of knocking...so yes that makes sense lower octane requirement. But is
    that effect enough to jump from, say, 89 to 87 octane? I doubt it.

    The second effect is fuel formulation...for air quality reasons, gasoline sold
    in winter is quite different from that sold in summer. But the octane ratings
    don't change...so I don't see how that would matter.

    Sorry I can't be more definitive. Anyone else?

  9. #9
    Join Date
    Apr 2005
    Location
    Finland
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    26

    Default

    I have the BSR PPC sofware in the ECU and I'm using euro98E octane gas as suggested by BSR. I'm not sure though, which US octane is similar. I've heard that mileage should be better with higher quality gas, that is supposed to compensate the price difference.

  10. #10
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    Jun 2003
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    South Lake Tahoe, CA
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    Here at 6500 feet in South Lake Tahoe the atmospheric pressure is 80% of the pressure at sea level. So without a turbo the pressure in the cylinder is 80% of the pressure at sea level because the starting pressure is lower and the pistons compress the fuel mixture the same amount as at sea level. Back when I did my own work and measured the compression of my engines I was initially concerned about the drop in compression untill I thought about it. The turbo may complicate the issue. I don't know if it can tell if the air pressure is lower and compensate for it to give the engine the same charge as at sea level. I would think not. If it doesn't then 87 is fine because the engine is detuned at altitude because of the lower compression. I always use 87 and have no problems. In fact I get great mileage numbers. abut 25 mpg at an average speed of 31 mph.
    Wait Griswold
    2003 XC70
    South Lake Tahoe, CA

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