The Windsor thermostat is not correct. Here is a picture of the correct thermostat and bypass plate. (Credit to MJ for his picture).
As George pointed out, the pump you have installed is incorrect too. All of the parts were designed to work together as a system. We know you have the wrong pump and the wrong thermostat. What we do not know is if the bypass plate was replaced. There is a bypass plate out there that essentially seals off the bypass port.
Here is the link to the proper thermostat but it looks like they are on back order.
Summit Racing shows them in stock and for a Cleveland but their picture does not show the bottom of the thermostat to confirm the "hat" is actually there.
None of this matters if you do not have the correct water pump. The FlowKooler and Edelbrock have an enclosed impeller designed to move more gpm. They also have the bypass port designed to work with the thermostat and bypass plate.
