Bubbling and gurgling in the cooling system is a sign that the system is properly pressurized and parts of the engine are hot enough that the coolant is flash vaporizing. This is a great way to cause parts to warp and other nasty stuff to happen. Begin with testing the pressure cap and making sure the system is fully filled-bled. If this continues you need to look for the cause of either lack of pressure or if the system continues getting air in it you need to find the source. This is often the early signs of head gasket failure or cracked heads.  

Dennis

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of Don Hanson
Sent: Saturday, September 12, 2015 2:58 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Thermostats...question(s)

   Is there an accepted method to test the function of one of our double
style thermostats?   I am skeptical about the proper operation of my
currently installed one.... lately....I have had some other issues with cooling and recently replaced my oil/coolant heat exchanger (mine had a pin
hole water leak to the outside).   But I also noticed once recently that I
could hear some bubbling in my coolant system when I shut the van off,  and I have not heard the fan recently.

   Anyhow, I have a spare used thermostat sitting on my bench, unknown condition....I'd like to see if it actually works and maybe swap that in....If no worky, what kind or brand should I buy to get a good dependable part?

   So can I drop the spare I want to test into boiling water and measure
it, testing for function, or some such?   It would be good to know, even if
I do just buy a replacement, that my spare is OK and working..
   I have calipers  to measure mechanical things.