Overheating starboard side of engine

[Carl]

What would cause only one side of an engine to run hot? I have mercury 150hp and the port side runs normal (this side has the temp sensor which sends the signal to the guage). The starboard side runs HOT !! This side houses the sending unit which activates the high temp alarm. I replaced the sensor and sending unit. The temp guage reads normal, but the alarm sounds. I found the the port side felt normally warm to the touch, but the stbd side was so hot that I could barely keep my hand on the head. The water runs well out the telltale.

Any thoughts?

Thanks