Pop the cowling and look down on the inside of that "tell tale" port. Follow the hose connected to it back to it's source. My current 3 and 4 cylinder engines plumb off the exhaust water jacket...a large, flat, aluminum plate on the opposite side of the powerhead. That is a separate water supply that is not thermostatically controlled due to the fact that if the engine is running, you need to keep exhaust components cool.
Putting your hand on the rear of the block, adjacent to the spark plugs and putting it on the plate can tell you if you have a circulation problem....if the plate is hotter than the rear of the block, which is thermostatically controlled, you have a circulation problem. If cooler, you probably have debris plugging the tell tale outlet.
Temperature to expect would be about 50* above ambient water conditions (on the exhaust manifold cover) in which the boat is operating, and the block temp would be determined by thermostat opening temp (100-143F range of t stats) and how long/hard the engine has been/is running. You can hold your hand on both these temperature ranges. After/while running hard, if you touch a surface and have to immediately remove your hand, you are too hot. Over temp sensors are 1
