I've also been told not to use synthetic oil in an aircooled Vanagon, for cooling, as AC VW's are air/oil cooled.  However, as a long time motorcyclist, I'm aware of synthetic motorcycle oils (such as Golden Spectro) which are specifically formulated for air/oil cooled motorcycle engines.
  So, you CAN have your cake and eat it too!  The only downside is Golden Spectro is very expensive oil.

   The Trundler
   '82 Westy
   '87 Westy

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