Putting a 160 thermostat in would NOT make the engine take longer to get to normal operating temp. If you coolins system is up to snuff it would NEVER get there. The purpose of a thermostat is to SET the normal operating temp. If you are running a 160 stat and your car is running 190 to 200 your cooling system is inadequate. A couple degrees above or below the stats rated open point is normal but if you are that much above your stat rating you have cooling system issues.