Is air getting into the cooling system a common, recurring problem with Vanagons?  I have an 85 with an inline 4 conversion.  The cooling system has gotten air into it again, this makes about 3 times in just a few months that I've driven this van. Once, I think I may have caused the 'airlock' when I changed the coolant shortly after acquiring the new ride and not having a Bently, I was not aware of the bleeding procedure..Then, after a bunch of new parts (water pump, temp sensors, thermostat, fan sensor, etc) I finally got all the air out, until a hose started leaking...Did the whole bleeding again after changing that hose and all was good for a few weeks of running...But alas, after storing the van for a couple of months while traveling, I returned and again began to see some odd temperature behavior  on the gauge...Not running where it normally did (down near the bottom of the scale, consistently)but going up to above 1/2 way for half an hour of driving sometimes, then back down to normal..Then, no heat from the heater...caused me to realize again I had the dreaded airlock...
  This time, I put the front way up, about 3 feet higher than the motor and even back-fed coolant into the radiator bleed screw after doing the air bleed/fill/bleed/fill for a bunch of times.  It took about a quart of liquid, with the motor off and the temp. down from running temp. when I hooked in a small hose and put a funnel into that, then poured coolant into the bleed screw hole...
  So, is this something that often happens to a van?  Do I have some kinda air leak in the system, or perhaps a leaking headgasket or some other problem?  Or am I just not getting all the air out in the first place?
  Help!  This is stumping me and I need to get it right as I am heading out to the desert soon and I don't want to have to backfill the bleed screw every few days...or whatever.
  Don Hanson