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Thermostats allow the engine to reach efficient operating temperature as quickly as possible. They are designed to open at a preset temperature. A 160 degree thermostat opens at approximately 160 degrees, the 180 opens at approximately 180 degrees. Once the thermostat opens it has no control over engine temperature unless the operating temperature drops below preset. In my opinion the 180 degree thermostat provides the most efficient operating temperature for the Ford Y Block engine. It allows the engine to reach operating temperature fairly quickly which helps eliminate condensation and the black spatter on the rear bumper and trunk.
I have always considered the Robert Shaw Thermostat made by Cooper Standard to be one of the best. It is a brass thermostat similar to original equipment and has the largest opening available. This type thermostat is now being offered by Mr. Gasket and can be purchase at Summit Racing, Auto Zone and other parts stores that carry Mr. Gasket products.
Do not order by application, order by Part Number 4367. It is packaged for Mopar Big Block Engines but works perfectly in the Thunderbird and other Ford Y Block engines.