I'm in the throes of sorting out the cooling system, and some other
opinions would be welcome....

A friend ( who knows the vehicle) drove it across town  for ten minutes
or so Saturday, and it started to overheat. She turned on the heater to
get some more cooling going, and pulled over at the earliest chance,
parked. Well done I say!
But odd. The system was working fine the day before. In downtown traffic
too. 

I took the van back home next day, found a warm hose to the rad, cold
one to the water pump. Replaced the thermostat with one I tested.  No
change.  Hear hiss of air when warm engine is turned off. Noticed water
coming from the water pump housing when engine running ( remember this
is an I4 1800 jetta motor, with an I4 jetta one hose expansion tank).
Pulled the pump and housing apart. Housing has
corroded/worn/disintegrated  from the inside and there is a pin hole in
the housing allowing water out & air in. 

Replaced entire waterpump & housing with new one. Top up with water as
test. Still hot engine/cold rad. Took out thermostat and ran engine with
no thermostat. Hot engine cold rad and cold heater. Pulled rad hoses
with engine running.

Got very wet. Ick. Ick Ick Turned engine off.

So there is water going to rad! Pulled radiator. Took to shop. Flow test
shows water runs through, but because of the "baffled design" of the rad
( shop guys words)  it is difficult to tell how good the rad is. But the
suspicion is that radiator  is working well enough. Conclusion: one huge
vapour lock in the system somewhere........that is completely stopping
water from circulating through radiator. 

Now, I've replaced the fluid/bled the system  in this van before, (
pulled the radiator; changed the expansion bottle; changed the heater
core; dealt with leaky expansion tanks) and done it with the non
standard expansion tank I'm using, but I have never had a problem like
this one....

Oh great and widely experienced list, any suggestions?

Bill M.
'82 Jetta powered GL ( in several pieces at the moment)