"Thermostat would have no effe
"Thermostat would have no effect on 'pee hole' discharge.
It strictly regulates water flow around cylinder and head.
Manifold and exhaust have a constant flow, with most exiting with exhaust.
The 'pee hole' is to confirm water flow, but it can be plugged while water continues to flow through exhaust. Its plugging would be a symptom of other possible restrictions and thermostat operation could be affected by that.
And of course, a problem with water pump would also be evident by lack of 'pee hole' discharge as well as overheating.
Remove the 'pee hole' line at manifold and run a pipe cleaner in to check for blockage at that point, the bypass tube at top is where water enters manifold (as well as from block when thermostat opens)."