1977 omc i/b

HELP, i have put in a new impeller, thermostat,and the water pump is good. I take the boat out it started getting hot ( i was in the no wake zone ) so i gave it some throttle to turn around and head back when the temp started going down, drove around 1 hour no more heat up. Next day same thing but when i gave it throttle it stayed hot so i limped it back to the dock and 5 feet from the dock the temp when down and never heated up again, please help im at wits end and i cant afford to take it back to the shop. the boat is a 1977 pontoon with a 120 omc i/b motor

test for water to the t-stat

Post # 4

There is a zerk fitting inside a hole on the front of the drive above the cavitation plate insert the tip of the grease gun and shoot it with 5 shots of grease.