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.