You`ll experience more engine wear with cooler temperatures so run it as warm as you can within safe parameters. Remember though that thermostats only start to open at their designated temps and usually aren`t fully open until they`re about 20 degrees above their designated temperature. A lower temperature thermostat will not necessarily make your engine run cooler it will only start to open at that temperature. The running temperature of your engine will depend more on the radiator, water pump, fan, and shroud than your thermostat. A 180 degree thermostat is the norm. I`ve run a 185 for years without any problems but you`ll have to toy around with your car and climate to see what works best for you.