Is the rad fan kicking off and on properly, with both speeds?  If not this could be why sitting still is overheating/ ovrpressurizing the system.
  I've installed a a manual bypass high-speed "ON" switch in the blank space on the instrument cluster, using a junkyard rear window defogger switch, tapped into continuous power on one side and rad fan high-speed feed circuit on the other side of the switch.  It's slick, and has come in handy a few times!

Mike B.  
  ----- Original Message ----- 
  From: Jeff Lincoln 
  To: vanagon@GERRY.VANAGON.COM 
  Sent: Wednesday, December 16, 2009 1:40 PM
  Subject: Re: 2.1 Cooling System Oddity: Since we are on the topic of coolant issues. (kinda long)

  Thanks Greg and Dylan - Your experiences and explanations really helped. I'm
  sure this must me the problem. I love this list.

  >

  --
  Thanks,

  Jeff
  '90 Carat (Grover)
  '86 (We call this one Parts)
  '78 Bus (Melissa) Patty's Bus