We have a problem with our dear 85 Vanagon.
It overheats. This is what we observe:

There is a leak in the rear heater. We change that plastic bleeding
screw and the severe leaking stops. But there still is a bit of 
leaking. Heater core?

When we unbleed the cooling system following the procedure in the
Bentleys the car runs fine for a while. But then the system pushes
liquid out and into the overfill tank (the tank behind the license
plate). Well, if there's too much pressure in the system that is 
what is supposed to happen, but the liquid doesn't get sucked back 
in and there is air in the system. That then leads to overheating.
This phenomenon now happens very fast, we can't really drive the 
car any more. If somebody out there has an idea what we could do
or how we could systematically find the mistake, we'd be the most
grateful people in Seattle!
Somewhere air must  get in or do we do the unbleeding in a wrong
way?
We only have a vague idea of how exactly the cooling system works,
like what are the pressures in the system, if you go at 2000 rpm
you apparently change the pressure to some different value, what 
is the function of the bleeding valve in the engine compartment
(it says to open and close it somewhere during the procedure and 
we do it but don't know why, nothing comes out there). Are there
any tricks while unbleeding the system that we are missing. Maybe
we don't get all of the air out and then when the coolant gets warm
that air expands more than the liquid, the pressure pushing liquid 
into the overfill tank ... Maybe air gets in through a leak l....

Need help...

Rainer and Corey
85 Vanagon