Yes on both counts as long as the system has no leaks to the outside other
than the working pressure cap.  If you do have combustion gasses going into
the coolant it's bad because there are nitrogen oxides (NOx) in the gasses
that will create nitric acid in the coolant.  This will overwhelm the
anti-corrosion inhibitors quickly and dissolve your engine from the inside
out.

You likely have combustion gasses.  Have someone sniff the pressure bottle
with an emissions tester.

Stuart

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Tom Carchrae
Sent: Monday, September 09, 2013 3:05 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: A Different Coolant Problem

Sure.  And no doubt that steam in the engine is a nasty cycle, with
air/steam pockets creating more/bigger hotspots.

However, once cooled, if there are no combustion gasses, then all the steam
should disappear, right?  When that happens, it will draw coolant back in
from behind the licence plate.  The only time it could leave air is if (a)
it was combustion gases or (b) if the tank behind the plate was empty, or
(c) the cap or pipe (to the reservoir behind the plate) has a hole.