Here is the proceedure for bleeding the air out of the system.
1. Jack up the front of the van at least 16".
2. Remove upper grille
3. Crack the bleeder screw on the top of the radiator (upper left).
4. Make sure heater controls are in the full "on" position.
5. Start van
6. Open coolant expansion tank.  (remove the pressure cap)
7. Add 50/50 mix of coolant as needed and let the engine warm up a little.
8. After a couple minutes of warm up rev the engine up to 2000 rpm and hold
it there.
9. Continue to rev engine and add coolant to tank until a steady stream of
coolant comes out of the bleeder screw on the radiator. (you should have an
assistant watch it for you).
10. Put the cap on the expansion tank and close the bleeder screw
11. Shut down the engine and let it sit for 5 mins
12. Start engine and rev up to 2000 rpms before removing cap from expansion
tank.
13. Repeat steps 9 and 10
14. Shut down engine.
The system should be properly bled.  If you are really paranoid repeat this
process as many times as you like in order to make you feel better (there is
always the psychological aspect of van maintenance).
If you still have overheating problems then I would suspect your radiator
(too much bars leak).  I sell these new for $175.
Also check the waterpump for play in the pulley (signs of a worn out pump)
while you are at it.
Let me know if I can be of more help to you.
Ken Wilford
Van-Again
John 3:16