If like later model engines, and no reason why it would be all that different, the impeller is in your water pump assembly which is just above where the lower unit and mid section join.....the pup is attached to the lower unit, and can be seen on top of it when the lower unit when removed. It receives it's input water from the small holes in the lower unit housing.
The output of the pump is on top of the pump casting and via a copper tube goes into a grommet in the bottom of the engine block. In the engine block it cools the engine and in discharging, cools the midsection of the engine and exits the center of the prop......through hub exhaust system.
Just below the cowling on the rear of the engine are ports that allow "exhaust gas relief" for when the engine is running in the water and the boat isn't moving....some cooling water may come out there also , with exhaust gassesamount depending on engine rpms.
There is a small tube that runs from the exhaust manifold (flat plate on the left side of the engine viewing from the rear) over to the other side of the engine and just below the cowling exits a stream of water when the exhaust manifold has enough water pressure (from filling with water from the pump) to force water out.
