Jason said:

i was talking with a buddy of mine recently.  his name is wolfgang, an old
school vw mechanic from germany who went to vw school and all that jazz.
anywho i was asking him about installing the tstat that is available that
opens at a lower temp then the stock vw tstat.  i think the one is for audi
but i am not certain.  i believe the difference is 85 degree c versus 80
degree c. not too big a margin, but definetely a difference.  anyway, he
told me to stay away from this because our vans (mine is a 90) need to run
at a certain temp in order for certain sensors to work properly ie; fuel
injection, tII switch, etc....  he claims that if the van is running cooler
then certain signals are not getting passed throught the ecu properly thus
not letting our vans run properly.  he says that they are designed to run a
little hotter then most cars and thats just the way it is.  does anyone else
know anything about this?  it sounds reasonable but i am still not sure.  i
would like to make my van run cooler but if it was desiged to run hotter,
then who am i to change it.

Chris says:

Think about it Jason, if our vans do not run 'properly' at cooler temps, how
do we get them up to operating temperature in the first place?  I think what
your friend meant is that the system is optimized for the 85C thermostat and
running consistently below that temperature will compromise overall system
performance to a degree.  I think running with the original spec thermostat
is a sound idea.  The cooler thermostat does not increase the cooling
system's heat-removing capacity anyway.