overheat problem

[Doghouse1]

I have a 1996 70 hp yamaha outboard. The engine overheat alarm goes off occasionally only at idle. I have replaced the thermostat and the water pump was replaced this spring. I recently purchased a heat sensor gun to monitor engine temp. The engine usually runs between 120 and 160 degrees. The overheat alarm goes off only at idle when the temp gets to about 180. Is this the temp that the sensor should go off or is the engine really overheating at idle? Should I replace the sensor?

Thanks for your help.

[99yam40]

you can pull and test the switch to see if it operates within the specs in the service manual