Pictures and description of the not often discussed (or even known about in some cases) thermostat bypass valve ~ restrictor valve that's located in the hose that goes from the bottom of the manifold at the T-stat end down to the water pump.
Orientation is with the small hole shown in 2nd pic toward the T-stat.
Valve opens due to coolant flow pressure when T-stat is closed to recycle it through the water pump and directly back into the engine for faster warmup. When T-stat opens, the relief of pressure cause the valve to close and restrict the majority of coolant flow so it goes through the T-stat instead, and thus through the radiator for cooling.
Outright removal of the valve on engines so equipped can cause overheating issues as too large a %~age of the coolant recycles through the wide open hose to the water pump and right back into the engine instead of going through the radiator to cool.
This is the alternate system used in place of the type of T-stat that has the disc on the bottom to restrict recirculation flow when it opens.
Pics of the actual valve itself as supplied by BattleBug a couple years back:
More pix added as supplied by Pat Garrett