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Thread: what type of fuel

  1. #1
    Join Date
    Feb 2009
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    4

    Default what type of fuel

    What type of fuel do you use in your xc90? I hear that 91 is recommendd but regular 87 can be used also. If I use the 87 octane am I doing any damage to the car/engine or just a lack of performance.

  2. #2
    Join Date
    Nov 2004
    Location
    Double Oak, TX
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    Default

    87 will lower performance due to retarding of the timing. It usually has less
    detergents also (that is one of the things you pay for in premium)

    We run mid grade around town, dont need high performance taking the kids
    to school. Out on a trip we us premium, going 75 on the road.

    I can tell when my wife fills it with regular, the shifting changes.
    2000 F350, 4x4, Crewcab, 7.3L Turbo Powerstroke Diesel
    2005 XC90 2.5T OSD 06/2005

  3. #3
    Join Date
    Oct 2008
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    socal
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    Default

    With the high hp to displacement ratio, the compression ratio on these engines are usually high so it will knock with lower grade fuel. The ECU via the knock sensor will detect this and retard the timing to compensate for low octane fuel. This should prevent the main source of engine damage but performance may suffer (power and mpg).
    From most sources, I heard that this feature was designed for occassional use of low octane fuel due to availability issues, so I'm not sure about the long term effects.

    I believe some tier 1 brands like Chevron uses the same additive/detergents package in all of their fuels (amount may vary by octane rating) and some brands rumored to not have any additives/detergents at all for any grade.

    I would be curious to know if you see a drop in mpg and how much that drop would be. In SoCal, the price premium between 87 and 91 is about 10% with 87 @ $2.20/gal. My guess would be a 2-5% reduction in mpg that would help blunt the cost of 91.

  4. #4
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    Jan 2009
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    Massachusetts
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    My dealer told me not to bother with the 91 unless you are towing or driving under stressful conditions (extreme temps, excess speed or long slow). I ran about 7 tanks of 91 and am on my 5th tank of 87. I have not noticed anything other than slight MPG difference.

  5. #5
    Join Date
    Nov 2004
    Location
    Double Oak, TX
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    Dealers tell you what you want to hear when it benefits them, and will tell you you
    dont have an issue with the car when it benefits them. They tell you 87 because it
    will get you to buy the car because it doesnt need premium. How may of the sales
    people even know where the car is built, they just came from the chevy sales lot
    down the road. Mechanic doesnt car what you run either, if it carbons up or gums
    up, they get money to fix it. Remember that repair money is what keeps a dealer
    in operation..

    So run what fuel you want, the dealer will love you for it.
    2000 F350, 4x4, Crewcab, 7.3L Turbo Powerstroke Diesel
    2005 XC90 2.5T OSD 06/2005

  6. #6
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    Oct 2008
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    Default

    Just to clarify my post,

    The engine is designed to run 91 on octane (based on the compression ratio of the design) and can retard timing due to knocking with ocassional lower grade fuel (primary source of damage). I belive this feature (knock sensors) was part of the EPA OBDII requirement to address local fuel variations so hence the conclusion of ocassional use of 87. It will cause a loss of power (you may not be using the full power) and a loss in MPG (need more gas to get to power level you are used to seeing). There are some recent engines (post $4 fuel) designed to run on 87 to 91 (like the new Hyundai V8) with the assoicated drawbacks but I don't believe the Volvo is one of them

    IMO, I would think that the designers would have more knowledge over the dealers so I always run 91 on my cars that are designed for it. Kind of reminds me of a joke on what auto salesman, auto mechanics, and medical doctors have in common...they can never say "I don't know to a question". Heck, my Volvo dealer told me the replacement T6 transmission with the improved internals is more reliable on transmission #2 yet didn't have a line to explain why transmission #3 will last longer then the other two. Its hard to know if the designers spec'ed 91 due to emission, mpg, and marketing peak HP/torque # or due to some other 2nd order reliablity effect.

    Studies have shown that detergents in fuel reduce carbon buildup. My point was don't assume 91 always has good detergents and 87 doesn't offer any cleaning abilities. The detergents is more a function of fuel branding (product differentiation) then octane rating. The website offers some insight on the min. federal additive requirements and what the better additives do (http://www.toptiergas.com/). IMO, my other cars (390HP/4.2L and 450HP/3.6L), I do see a noticable difference between gas brands @ 91 then compared to the two XC90s (311HP/4.4L and 260HP/2.5L) at 91 or the old fashion 210HP/5.0L pushrod V8 at 87.

    These days, the cost difference between 91 and 87 can't be neglicted and I don't believe that the lower octane gas will damage your car from knocking like in the old days. However, it may be worthwhile to pay a bit more for a gas (91 or 87) with a better additive.

  7. #7
    Join Date
    Jan 2009
    Location
    Massachusetts
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    Check out page 115 of 2007 XC90 (USA) and it clearly states 87 octane is perfectly fine to use and will not cause any engine wear. It states for optimal performance use 91 or higher. So my dealer was actually right.

  8. #8
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    My manual says 91 is what the engine is designed for to meet its power and fuel economy rating and allows a min. rating down to 87 without damage (mainly due to knocking by sensing knock and reducting timing). It also says on the previous page to use fuels with detergents so just not any 87 octane fuel.

    I think your dealer was expressing on opinion that assumed that the 91 condition only applies if driving under stressful conditions or towing. From the manual, the message I get is use 91 if you want your car to perform as designed.

  9. #9
    Join Date
    Mar 2009
    Location
    Colorado
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    Altitude also effects octane. If you live at high altitudes, the premium is not as necessary since there is less oxygen. I find our XC90 runs as well on 87 octane as 91 octane at 6000+ ft. Since we live at a base altitude of 8000 ft and everything is up from the bottom of the valley I only run Premium on rare road trips. No noticeable performance changes with mid grade.

  10. #10
    Join Date
    Mar 2009
    Location
    Denver, Colorado
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    5

    Default Colorado

    Agreed - I have always run 85 in everything I own, and never had any problems. besides more HP!

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