ir3333, the thermostat controls the minimum operating temperature in a running engine. At startup the thermostat is closed. To allow circulation and prevent hot spots the bypass allows coolant to circulate. When the coolant gets up to the thermostat opening temp, it begins to open allowing a bit to flow to the radiator.The full open temp is generally about 20°above the advertized temp. The design Delta T across the radiator is generally 10°F to 20°F.
After searching more, the A/C water pump has fewer vanes but the pulley ratio is different to speed up the fan speed to draw more air. The lower vane count on the WP impeller keeps the coolant flow similar and prevents cavitation in the pump.
For the problem that started this, it appears from his photos that the shroud and fan spacing is a major factor. Making a "die" and rounding the inside diameter to bend the aluminium toward the engine will help airflow. This should be just 1/2" around the perimeter of the fan hole. The the fan should be spaced ahead a bit or the shroud spaced back a bit, to get the fan 1/4 to 1/2 inside the shroud and the rest outside. If it still gets warm the A/C WP and pulleys should be installed.
