[Vwdiesel] ideal thermostat temp for 1.6 TD

[carstuff]

So, i've learned to hate German engineers for hiding the thermostat on the otherwise wonderfully designed 1.6 (TD) engine.....  I have a question for the collective knowledge & experience here:   What is the ideal thermostat temp for this engine?   What I removed when investigating was a VW/Audi issue 87C deg thermostat (approx 195 deg F).   I've gotten conflicting info from parts sources whether the 87C or a slightly cooler (75C/180F) is the correct one for my engine.   The original problem was the appearance (by gauge) of running hot & a large enough temp increase with the AC to question the integrity of the cooling system.   For mostly rather warm-weathered southern US driving, what would be the thermostat to use?

relatedly;  what is the cleanest/simplest/preferred coolant refill method ?

thanks
-chris g