Heat sensor

[mr.bass]

Friend of mine has 200hp Mercury outboard and at 3500 rpm's the overheating buzzer sounds. Changed impellar and all parts with kit. Replaced thermostats (2) and still buzzing. Could this be a heat sensor bad and is it located just below top plug on right side of motor looking from the rear of motor.Any help would be appreciated.

 

[tlh 178]

could be the popet valve, when was the last time it has been serviced.

 

[Texasmark]

The poppet valve bypasses the stats at the higher rpms (2500 I think is the design value) allowing no thermostat control (water is cooler than 143F usually and the stats close off) and a much higher flow rate for the higher dissipation in the power head with the higher rpms. If like my son's 150, at the center of the block up on top, behind the flywheel, is an ell fitting (about 3/8") with a hose attached that goes down the back of the engine and connects to a fitting just above the cowling at the bottom of the powerhead. The poppet is in there and dumps into the mid section.

Mark

 

[mr.bass]

will let my friend know what you both have said. Thanks a bunch.

 

[Chris1956]

To be clear, the poppit valve is located low on the starboard side of the powerhead. You normally need to remove one side of the lower cowling to access it easily. There are several different designs, and it is necessary to get the correct parts to rebuild it.