what is the difference between a 195 thermostat and a 180 or 160' what does it mean

Well use the 195° thermostat for a base. The 180° thermostat is 15° cooler than the 195° thermostat. The 160° thermostat is 35° cooler than the 195° thermostat. So depending on the thermostat you put in your car, thats is around what temperature the engine will run at. Vehicles use a 195° thermostat mostly.

The only reason for using the lower temp thermostats is if you are running a really high-performance engine that's making a lot more heat or you live in a really hot climate. If you run a lower temp tstat in a stock engine, it can cause it to remain in "open loop" longer than desired and harm gas mileage and performance. In other words, stick to the factory tstat temp, unless you've made a lot of custom engine mods.