Thermostat choice for my Duster 340

the thermostat can control the temperature....to a point,
If your system is functioning properly a 180 should run around 180 - 185.Change it to a 195 and it should run 195 - 200.A cooling system that is inadequate will find it's own temperature irregardless of the thermostat.
a 195 degree engine is more efficient,cleaner,reduces engine wear and arguably makes more power than the same engine operating at 160 or 180.
Guys freak out when their engines reach 200 degrees but nearly all newer engines operate well above 200 normally.