Single weight vs. multi weight

Discussion in 'Oil' started by Jick Scott, Apr 6, 2009.

  1. Jick Scott

    Jick Scott Member

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    How much faith should I put into a mechanic telling me.... single weight oil for air cooled engines and multi weight oil for water cooled engines?
     
  2. TQuentin1

    TQuentin1 Well-Known Member Staff Member Moderator

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    Do you have a bike? I don't see any mention of one in your profile. You might add that to your Avatar.

    TQ
     
  3. NEWHD74FAN

    NEWHD74FAN Experienced Member Retired Moderators

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    Actually a mechanic making a generic statement oil viscosity statement based purely on air or water cooling is not thinking with all cylinders firing. It would basically negate all the progress in lubrication and engine design in the last 75 years or so. While it is true water cooled engines maintain a narrow heat range, to specify oil based purely on that limited knowledge, when considering the vast scope and range of environments, engine types and uses a modern engine is put through.
     
  4. glider

    glider Veteran Member

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    Find a new mechanic! :s
     
  5. DavHJ

    DavHJ Member

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    well my engine manual for my boat engines call for straight 40 weight and they are fresh water cooled.
     
  6. glider

    glider Veteran Member

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    Boats are considered severe duty unlike other vehicles.
     
  7. slimjim47

    slimjim47 Member

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    He's partially correct. The FSM states both multi and single weights. It depends on the temperatures you're riding in.
     
  8. NEWHD74FAN

    NEWHD74FAN Experienced Member Retired Moderators

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    There is a lot said in the FSM (Factory Shop Manual), but the key here is most modern HD motorcycles fair well with 20W-50 Synthetic or good multi-weight for 2 key reasons...

    1) Modern engines even though mass produced are built to tighter tolerances and run at higher temperatures and pressures making the 1st few seconds while oil pressure is rising, to pump oil in key locations to prevent the premature wear. This may be in the humid tropics, dry deserts, cold and wet northern plains or even drastic temperature shifts for -30 deg F in the mountains to 140 deg F in the valleys, sea level to 5,000 Ft or more in the mountains when ridden long distances at fairly high rates of speed. Single weight likely will likely come up short, unless the bike is a garage queen.

    2) Since motorcycle use can be in extremely cool or hot environments, asking 50-60W oil to flow in cold weather is expecting too much for an oil starved engine with oil flowing like thick syrup, and for longer service intervals expected, corrosion and oil breakdown is more likely to occur. If you are using a modern motorcycle, use what is recommended, multi-weight oils w/ anti wear, corrosion and synthetic to also help combat extra heat a V-Twin will make under todays EPA mandated lean and low emissions environ.