Testing Thermo Switch on 92' Pro 60

[JPJ]

Hello,

I have a 92' Pro 60 tiller. I have had overheating problems in the past and before the open water season gets under way again I want to figure this out. My motor periodicaly overheats. I have put in a totaly new water pump (plastic housing,impellar, cup,gaskets,stainless steel plate, grommets....). I installed a new Thermostat, all these parts are OEM from Yamaha. What is confusing me is, it doesn,t overheat every time.I should mention it only overheats at idle or *****ing slowly.Sometimes when it overheats it will do it early on then be fine the rest of the day. I am thinking , could it be my Thermo Switch? Can this give the motor a false reading of being to hot and cause the motor to go in the safe mode. Has anyone else had this problem, and if they have. Where you able to find out the problem and fix it.

[99yam40]

check to see if that motor has a PRV that is sticking open sometimes and dumping too much water to cool motor at low RPMs.
Other than that you can pull and test the temp switch to make sure it operates in spec

[boats.net]

Overheat sensor should activate when reaches 183-194 degrees, can test test by putting in a pot of water and heat up until get continuity across two sensor wires.