Sounds to me you may have a bad cap. Sucking the coolant means there is a
place for it to go. The cap should hold it in  when the revs drop down.
After a few cycles the internal pressure should equalize and a quick test is
that the hoses become hard, like 12-14 psi hard. If there is air in the
system it will eventually find its way to the main pressure bottle and then
work its way out. A final check is to rev the engine and see if you are
getting a steady stream of air bubbles into the recovery tank. Some is
normal after a system fill but eventually there should be no bubbles
visible. If bubbles persist or can be created by throttle-load then you have
a leak most likely from the heads. Loose heads make this extremely load and
time dependent.

Dennis

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Tom Carchrae
Sent: Monday, April 29, 2013 12:55 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: coolant overflow fears and thoughts

> The old hose definitely had holes in it; I tested by partially
> submersing
>> it in water.  The new hose is airtight - and clear - and I saw how it
>> sucked fluid up from the overflow tank when the engine started.
>
>
> That last part seems backwards.  When the engine is started and is
> getting warmer, the expansion of the coolant in the system should
> force liquid or gases, whatever is at the top, out of the pressure tank
and toward the
> overflow tank.   When the system is cooling down the coolant should be
> sucked from the overflow tank.
>
> Have you tested your pressure cap?
>

When I rev the engine, the pressure tank always sucks fluid down - the
reverse when the revs go down (barfing coolant onto the exhaust - mmm).

I agree with what you are saying when the system has heated up, but I had
just turned on the engine and went to check and, thanks to the clear hose, I
saw it had drawn fluid up.