I replaced the engine in my '83 water-cooled vanagon with a new updated '84.
 The installation went well as I had some motor-head assistance to make up
for my complete lack of knowledge.  With the Bentley book in hand the
insallation was a near success.

We did not properly bleed the cooling system of its air.  This came to a head
when I was using the vanagon as a giant flashlight with the engine idling for
some thirty minutes.  It seems an air blockage kept the coolant from reaching
the radiator and the poor thing heated over :(

Well I shut the poor thing down and topped it off, got it to my local shop
where the mechanic and I tried to bleed the system of air.  Following the
Bentley book word for word, I believe we did an excellent job.  Well two
weeks later, new snow tires and all we climb in the rig for a Christmas
shopping road trip to Burlington VT in one of New Hampshire's first snows of
the season.  The journey went without a hitch, EXCEPT, we lost the heat
intermittently and the temp needle did a dramatic climb (clutch-in coast on
the interstate brought the needle back where it stayed until it was time to
drive back.)  So, having gained much insight and mechanical aptitude over the
past months (I am turly indebted to this beast for imparting such knowledge)
I have diagnosed the problem as air in the system.

So, I tried to bleed it again this past weekend by parking it on a slope on
our property (I am not certain the front wheels were exactly 40cm higher than
the back--at first it was more, then a I rolled down the hill to reduce the
angle).  I was only getting air out of the radiator---intermittently i could
get a gurgle of coolant but not consistent and I could hear a certain
gurgling\swishing\whitewater rafting sound down in the radiator.  When I had
made the trek back to the engine for the nth time the expansion tank was
below minimum and quite near the coolant hose outlet height, so I removed the
tank cap to add more coolant but before I could a massive backwash would come
up and out of the tank onto my cold hands and down to my shoes.

There is the background.  Here are my questions:

Have I done any permanent damage from the first boil-over?
Where is the air coming from?  Could it be what was referenced by Patrick
yesterday?
What am I doing wrong when I am bleeding the system?

Any general directions (or specific instructions) would help me out a bunch.
 My love-hate relationship with this nearly perfect red & white beauty always
comes back to the smile on my face when I hop in the pilot's seat and cruise
the white mountains of NH (and surrounds!).  Please help  me get this baby on
the road again.