I have an 82 diesel to 92 digifant Westy.
This is how I bleed the coolant (radiator).
Works for me every time.
Park the van in my driveway, slightly uphill.
Use my vacuum source, oil thing that sucks oil from Griots Garage.
I flush the system and add new coolant mix.
Open the bleed screw a bit and suck out all the air.
Soon, only coolant comes out.
Works perfect.
I can run uphill at 70 mph, with a/c on, at 105 degF and my temp stays right
in the middle.
yes, it is true, my diesel Westy has a/c.

Lots info
http://home.jps.net/~shilohz/vanagon.html