I asked this on another site and never did get an answer. Hoping somebody here can clarify and recommend which thermostat I should use. My NAA does not have a thermostat and never reaches operating temperature at least it never registers on the temperature gauge and I know that the gauge works. Looking on different online store sites...most online store sites only list one thermostat for my model tractor NAA which is 160 degrees until I looked at Dennis Carpenter which list 168, 172 and 188 for the years 1953-64. Can anybody clarify why they list three for these years and which one I should be using.