RW> The oil may not be, but the polymer additives they use shrink or expand   
   RW> at   
   RW> those temps changing the viscosity along the way.   
   RW>    
   RW> As you suggest, pure engine oil will thin out at higher temps.   
   RW>    
   RW> I can varify that by a story my dad used to tell about his earliest   
   RW> experiences with cars in the 1920s. In the winter they would build a fire   
   RW> under the engine's oil pan to thin out the oil before they 'hand cranked'   
   RW> the engine to start it. Of course, that was before multi-weight oil was   
   RW> invented.   
      
   Interesting..  I didn't know about the polymer additives that effect the   
   viscosity in different temperatures.   
      
   I scheduled to take my Monte Carlo back to the engine shop because there   
   appears to be a small leak somewhere around the oil pan gasket.  I wouldn't   
   normally be concerned, but it is still under warranty for 2 more years.  If   
   that gasket needs to be replaced, that is a pain!  You have to drop the   
   sub-frame!   
      
   While I had them on the phone, I ran the lifter tap (on cold start) question   
   by them.  He said not to worry about it unless you hear that noise all the   
   time while driving.  Under a minute of tap on warm up on those engines appears   
   to not be unusual.   
      
   He didn't think that changing the oil types would make a difference and said   
   to stay with 5w-30 (I have always used 10w-30).     
      
   I believe it is worth trying 10w-40 or 5w-40 - as I really don't see that   
   causing any problems.   
      
   - Mark   
      
   --- WWIVToss v.1.50    
    * Origin:  http://www.weather-station.org * Bel Air, MD -USA (1:261/1304.0)