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Premium fuel in 2-cycle engines

Discussion in 'Lawn Mowing' started by probe1957, May 15, 2006.

  1. probe1957

    probe1957 LawnSite Member
    Posts: 165

    I lurk a lot here but never post. I heard something this weekend that I have never heard before and wonder if there is anything to it. I figured surely you guys would know.

    I bought a new, Stihl blower. I also have a Stihl string trimmer and chainsaw, all, of course, two cycle engines. I have always used regular, 87 octane unleaded gasoline for my mixture. Which brings me to my question.

    The guy at the store says Stihl recommends using premium, preferably 93 octane fuel in the mixture. I have never heard of that. Is there anything to it?
  2. lawnmaniac883

    lawnmaniac883 LawnSite Silver Member
    Posts: 2,613

    The engines run better IMO on mid grade fuel. Stihl recommends mid grade (89+) not premium. There will likely not be any ill effects by using regular gas in your equipment.
  3. desert rose gardening

    desert rose gardening LawnSite Senior Member
    Posts: 387

    Do what you can afford. I have never used high octane in any of my engines and they all have lasted a long time and work strong.
  4. lawnguy001

    lawnguy001 LawnSite Member
    Posts: 77

    Echo also says to use 89 + octane fuel for there stuff. I had carb problems on my trimmer that I wanted fixed under warranty. They said it was " bad gas" . They replaced the carb and covered the repair ONLY after I showed them receipts for premium gas.
  5. dcplace2004

    dcplace2004 LawnSite Senior Member
    Posts: 423

    handheld blower:

    Use mid-grade unleaded gasoline with a
    minimum octane rating of 89 (R+M/2). If
    the octane rating of the mid-grade
    gasoline in your area is lower, use
    premium unleaded fuel.

    Fuel with a lower octane rating may
    increase engine temperatures. This, in
    turn, increases the rick of piston seizure
    and damage to the engine.

    -----------It does not say use a minimum of 93, or a minimum of a premium gasoline...it says a minimum of 89...it does not say 89 + either...it only says that if the mid-grade is lower then use the premium...it is the same for the 4 mix also...Do what the owner's manual says and you will not go wrong...I think that Stihl with it billions has more sense than someone that is a self-proclaimed expert...
  6. aDreamSoReal

    aDreamSoReal LawnSite Member
    Posts: 29

    All depends on the compression ratio. Any motor over 9:1 will benefit from 93. Under 9:1 use 89
  7. dcplace2004

    dcplace2004 LawnSite Senior Member
    Posts: 423

    We are talking about Stihl here, not any other engine...he asked about Stihl, and that is the information he should get...depends on compression ratios?...Actually, it depends on the owner's manual ratios...Even more actually, you can put whatever fuel in it you want - put diesel in it for all I care...we all have freewill...I am just pointing out what Stihl recommends for the engine to run properly and be covered under warranty...
  8. Fishboat

    Fishboat LawnSite Member
    Posts: 10

    When a warrenty is involved you're almost bound by having to do what they say to ensure a problem is covered, however adream's comment about compression ratio is the root of needing higher octane fuel. Higher compression yields more power out of a constant engine size(or weight). Given that weight is an issue with these tools it's not unreasonable for Stihl (or anyone else) to extract as much power as they can out of the small engines through high compression...and this compression ends up as a requirement for higher octane fuel. Higher octane has nothing to do with "power" as commonly thought...it prevents pre-ignition that low octane fuels exhibit when compressed over the 9:1 ratio.

    ...of course this is also why we don't run gas in diesel engines...as the compression there is somewhere around 20 or 25:1
  9. probe1957

    probe1957 LawnSite Member
    Posts: 165

    Thanks, gentlemen. I do read the manuals, but I must have glossed over the part about fuel.
  10. kmann

    kmann LawnSite Senior Member
    Posts: 298

    look in the owners manual. My new 550 uses 89.

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