Engine overheat alarm activates when RPM's exceed 3800. I have twin engines and it is the port engine that is affected. With a Yamaha mechanics help I have begun the process of elimination. So far we have checked the thermostats-OK, replaced both water pumps, replaced exhaust manifold gaskets on port engine, (per mechanics advice), Checked relief valve-appears OK, the engine still overheats and there is an obvious temperature difference between port and starboard engines. Both heads on port engine are too hot to touch for 2 seconds. Water flow with thermostat covers removed appears to be good and unresticted. All visible water passages appear free of obstructions. I'm not getting anywhere. Any ideas are welcome and I encourage any and all responses. Thank You, 
