Guys,
This may or may not apply. All of my Mercury motors I’ve been into have a pin hole in the copper water line. I believe it has a dual purpose.
The first application is so after running the motor, the water line in is still full of water. The pin hole allows the block to drain water from the cooling system to protect the powerhead from water intrusion.
The second app is to spray a small amount to help cool the exhaust cavity while running.
Robert,
I believe we still are missing something & I bet it’s simple as we are digging so deep. Seems Johnson was aware of this problem as changes were made very soon once into production. I believe the solution is in the service bulletin & drilling out an extra water output somewhere safe from the D-shaft splines or an additional collar was added to protect the D-shaft. Robert, I know about the Merc 4 cylinder motors. My Mark 30 is very hard to lift for this old guy.
Jeff