Thermostat Temp.

This is just for reassurance. what is the optimal operating temp for a 1995 Prelude S? I went to buy a thermostat from auto zone, and they only sold 170 degree thermos.... but i always heard that it runs more around the area of 185 - 190 degrees, which i cant find anywhere?? if that is true, would the 170 degree thermo. do any damage to my car, or just bad gas mileage, and no heat (which is already a problem for me) :banghead: I know it needs replaced, but i just thought i'd ask, for the sake of future knowledge. thanks!