Thermostat temperatures

I am sure this has been answered before but I couldn't locate it. I need a new thermostat, but am unsure which temp I need. The engine is a /6 and 3 different temps are available. 160, 180 and 192. Could someone please educate me on the criteria for selecting one temp over another? It doesn't seem like it should have to be this difficult, lol.
Thanks Guys
Author: admin