three possible sensors, dont know the specifics of the tbird, but call me at my work tomorrow and i can tell you.
but theres usually a fan switch in the rad, then either in the engine or in the thermostat housing will be a coolant temp. sensor for the ecu and one for the gauge or light.
possibly the gauge one is messed up, usually cheap, try changing it.
if fan isnt turning on, hook directly up to the battery and make sure the motor works, if it does,check the wires and/or change that sensor too, still should be fairly cheap.
160 is unnecessary for your car, put the 180 in, put a good 50/50 mix, and try and get most of the air out of the system if possible.