Jim,
I've been following this discussion but I think I missed something. 
Were you using a round MK3 Jetta Golf expansion tank?
Though you have already remedied your problem, I have some additional info.

The round globe MK3 expansion good choice for these reasons:
1. There is no recovery tank , the round tank spits excess coolant out to the ground
2.The tank outlet and hose is inadequate for the amount of coolant in a Vanagon system and the distance it must travel.
3. The Mk3 tank is designed to bleed the top of the radiator which is in close proximity to the tank, the tank being the highest point .
The highest point in the Vanagon at the top of the Vanagon radiator at the bleeder.
The size of the tank and two hoses are just too small for the volume of coolant the Vanagon has to process. 

Ive seen use of this small round tank in Vanagons before
Even if someone out there says it works for them, it still has the negative feature of spitting coolant into the environment, not a recovery tank like Vanagons are designed to use. 
Robert
1982 Westfalia 2.0 ABA

I LOVE the TD. Makes the car like a water boxer. 5 speed allows 65 mph cruise with 70 mph top. I have about 22k on it now.

Jim