Changing to a 160 thermostat won't make any difference. You have some other problem. Once the temp gets to 180 the thermostat stays open under normal conditions. Only thing that will change with a 160 thermostat is it will open sooner. If you put in a new radiator without flushing out the cooling system then your new radiator is probably got a bunch of crud in it from the block. Feel it with your hand. Start in the center and feel out toward the edges. If its cooler in the center and gets hotter toward the edges then its clogging up.
