Mercruiser Boat Project Cooling Water Flow Check HD

My project boat 1995 4.3L Vortec, Thunderbolt IV Ignition Mercruiser Alpha 1 Gen 2 heat gain check on water intake and cooling flow. I ran a Y-Valve on the garden hose to put one input into the barrel and one straight to the cooling coupler on the motor. That allowed me to check the draw of the impeller separate from the cooling flow of the on motor water pump, thermostat, and flow through the manifolds/risers/elbows, and out the transom. I was not able to work on the boat for six months due to a regular work project.