Thread: Overheating Mercury 40 horse

I have a 1996 Mercury 40 hp outboard that keeps giving me a beeping alarm. The motor is a 4 cylinder 2-stroke oil injected unit. I first thought that it was the low oil alarm but eliminated that by pulling the oil sensor wires...it still beeped. Then I got to feeling around on the head by the spark plugs when noticed that by cylinder #3 it was HOT. The rest of the head is cool to the touch. The motor "pees" water fine. What would make just that spot by the third cylinder get hot? Any suggestions would be greatly appreciated.

Thanks in advance,
Ryan

Thermostat?

If the surrounding cylinder walls are cool to touch and one is hot it might be a clogged inlet tube restricting the water from circulating around the hot cylinder. I would assume if the thermostat was bad they all would be hot. Just my 2 pennies.

Is the beeping a steady beep or an intermittant beep? Keep in mind most outboard thermostats open at 140°. So the motor is going to feel hot, but not so hot you can't put your hand on it for a few moments.