Turbojoe is correct, what's happening is the temp comes up in the engine, the thermostat opens, the cool water from the radiator hits it, the thermostat closes. Automotive engines used to do that too, until manufacturers started using bypass systems to prevent that. Ever notice your automotive thermostat has a block off plate on the bottom? when the thermostat fully opens, it closes the bypass. Since the connie isn't equipped this way, you can block the radiator partially to prevent over cooling during cold ambient temps. HTH, steve