Where is the thermostat on a 12 valve V6?

[Matt Ammann]

Hello Audi Fans,

I've been tasked with selling my sisters 95 90 S(sadly no quattro or I might keep it myself).

Unfortunately it is having some problems passing smog - all parameters are excellent, except for NOx, 
which is just marginally over.

I'm not sure what's wrong - Oxygen sensors seem good based on voltage meter readings. I do know
that the thermostat seems to be stuck open, as the engine doesn't warm up properly.  I'm kind of
hoping that if I can get the temp up properly, that it might eke through.

But in the absence of a service manual, I can't even find the thermostat.

Would one of you kind people please provide some clues to it's location, and tips for RandR?

Links to picture or diagrams would be even more greatly appreciated.

thanks,
Matt