John, what year is your car? If it is a late model with a computer control system the lower temperature thermostat may trigger a trouble code.
The calibration is set to run within certain parameters of engine temperature.
If it is not a computer controlled engine, I would go with the 180 degree. Remember too that a engine has to "burn off" condensation that is generated as a normal condition of combustion and an engine that runs too cool may not evaporate the water inside. Water in oil is a possibility then. And water is not a good lubricant.
Another thing is that engine oil should also be at normal operation temperature, a 160 may not allow it to get warm enough to flow as designed, kind of like running a very heavy (70w) oil in a stock engine. It may not flow to all areas with adequate lubrication to all metal surfaces allowing scuffing and excessive wear of barings, rings and on and on.