MH>RW> The oil may not be, but the polymer additives they use shrink or expand   
   MH>RW> at   
   MH>RW> those temps changing the viscosity along the way.   
   MH>RW>   
   MH>RW> As you suggest, pure engine oil will thin out at higher temps.   
   MH>RW>   
   MH>RW> I can varify that by a story my dad used to tell about his earliest   
   MH>RW> experiences with cars in the 1920s. In the winter they would build a fir   
   MH>RW> under the engine's oil pan to thin out the oil before they 'hand cranked   
   MH>RW> the engine to start it. Of course, that was before multi-weight oil was   
   MH>RW> invented.   
      
   MH>Interesting..  I didn't know about the polymer additives that effect the   
   MH>viscosity in different temperatures.   
      
   Oil Additiaves are an interesting area.   
   It you are fimilar with an Auto Tranny Fluid called "Trick Shift" it has   
   a Friction Improver in it that firms up the transmission shifts.   
   As I recall Ford used it for some years in their Auto Transmission   
   fluid.   
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