160 vs 180 thermostat

You have it now so that when the t-stat opens it never closes. They are supposed to cycle. Your mileage will likely suffer. Computerized engines are designed to run "whatever" thermostat they are listed to have. Differing from that can have poor driveability results. Lastly, if the engine does not get up to proper operating temp, you'll never get all of the contaminants out of the oil. Don't take my word for it. Look up something with a 6.4 in it and see what temp the fan kicks on. A lot of them kick on at 220 even 235. They are designed to run that hot.