The cap has two valves in it. There is the pressure relief that opens when
the pressure in the cooling system reaches the preset pressure, ~14 psi.
Then when things cool down and the coolant contracts the vacuum valve opens
to allow coolant to return from the recovery tank. Yes this valve does have
some resistance. This is why any leak in the system will prevent the
recovery function from working and in extreme cases cause the system to
loose enough coolant to become air bound. Then the weirdness's begin. Also,
get a pressure cap tester and some other tools and don't use your mouth to
suck on antifreeze. Leave your kidneys intact to process beer.

Dennis

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Bill MacLachlan
Sent: Tuesday, February 26, 2013 12:27 AM
To: vanagon@GERRY.VANAGON.COM
Subject: coolant overflow tank

Hi all.
Should the coolant overflow tank drain freely through the tube that connects
to the pressure cap?

I disconnected the connecting tube  at the pressure cap, tried blowing
through it into the overflow tank, but could not. Couldn't suck coolant from
the overflow tank either.
If I can't get coolant to move through the tube, how can the pressure tank
purge/replenish?

comments before I take the overflow tank off and apart :) ?

thanks all

Bill M
89 westy