Re: 1980 mercury 80 hp 4 cyl does it have a temp sensor built in?
The temperature sensor switch was mounted on the water cover on later models.------------Yours did not come with one.------Thinking of the day by owners and factory was that folks would visit the dealer for regular maintenance.---New impellers were installed all the time.--------Today with high labor rates folks do not visit dealers and repair shops.-----They just run motors till they come to a " dynamic halt " ----Then they buy another motor.----This is just my opinion and observation of they what things are today !-----It would be simple to mount a water pressure gauge on your motor.--I believe you can find the pipe plug on the water cover.