If the cap on the pressure bottle is working correctly,
It will indeed suck coolant in from the overflow bottle with repeated warm
up/cool down cycles.
I often don't bother to bleed at the radiator, and just monitor the level in
the overflow bottle and add accordingly for several days. 
Sometimes the suck back feature of the pressure bottle cap doesn't work like
it should, but it should.  
Scott
turbovans

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
John Runberg
Sent: Sunday, October 28, 2007 3:18 PM
To: vanagon@GERRY.VANAGON.COM
Subject: My turn for a cooling sys question

Attempting my first real bleeding after replacing the coolant tank.

As I bleed out air (and some coolant) should the coolant tank suck in mix
from the overflow tank and fill all the way back up after a few heat / cool
cycles? Or do I need to top it up? Dumb question, I know, but the answer
would be helpful.

john