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  • Meaning of SAE viscosity designations

    Discussion in 'The main mechanical design forum' started by rpchristian, Jul 10, 2012.

    1. rpchristian

      rpchristian New Member

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      Hello there,

      Can anyone point me to a good explanation of SAE viscosity designations such as, '10W40'? What does this mean in terms of dynamic or kinematic viscosity?


      Many thanks,

      Richard
       
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    3. flanzajr

      flanzajr New Member

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      oil viscosity designations explained

      use this link to get you started.
      http://www.mobiloil.com/USA-English/MotorOil/Car_Care/AskMobil/Viscosity_Designation.aspx
      The way it was explained to me years ago is that muitl-viscosity oils have specially designed polymer chains that flatten out at lower temperatures and curl up at high temperatures. This action allows the oil to act as a thin weight oil when the engine is cold or just started and as a thicker weight oil when the engine is up to operating temperature. So a 10w40 oil acts as a 10 weight oil when cold and a 40 weight oil when hot. The advantage is quick oil flow when first starting to lubricate parts immediately and then as a heavier weight oil at high temp to keep a good film of oil between moving parts. The disadvantage is that over time the shearing action in the engine tends to cut the polymer chains into smaller lengths, nullifying the multi-weight properties of the oil. That is why it is ALWAYS a good idea to change the oil in an internal combustion engine on a regular basis.
      Hope this helps.
       
    4. rpchristian

      rpchristian New Member

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      Excellent! Many thanks for that.

      RC


       

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