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RE: Changing coolant, thermostat--correction?

A couple of listers have stated that it's okay to use either green or
orange/pink coolant, but never mix them.

Yesterday I was checking out the coolant afterrun pump on my car ('91 200Q)
and had to refill part of the system with phosphate-free antifreeze.  The
dealer had flushed out the entire system just over a year ago, and refilled
it with the Audi blue/green (whatever it's called).  Anyway, my only choice
for phosphate and silicate free ethylene glycol (and SAME base as the Audi
stuff in this country, at least at the local dealer), is the orange Presone
5 yr/150k stuff.  That plastic bottle has, plastered all over it, that the
product is safe for all aluminum and brass radiators, and is compatible with
all other antifreezes.  I figure these guys (and gals, since the chief
technoloy officer there used to be a woman and is now undersecretary of
commerce for technology) at Allied Signal know their chemistry well enough
to be comfortable in that claim.  Bottom line: As long as you stay away from
phosphates in your coolant, you should be okay.  That's the one warning Audi
gives on coolants.

(Without pressing the point, this is a bit like the dire warnings about the
synthetic and non-synthetic Pentosins, and the dire consequences for rack
seals.  After a lot of digging, I found out that the significant difference
for systems operation is a slight difference in viscosity between the two
(11s is slightly heavier, in part because the system pressures in later cars
is lower).)

- Jim