Water temp guage reads hot

[gordhodgson]

I wondered whether anyone has experienced having their temp gauge start reading at 180 and go up from there after the engine is started? I have tapped the gauge and it went down with no power on, but as soon as I turn the key on it jumps to 180 again, the water pump is funtioning fine but I don't want to depend on the gauge as it will reach 240 at operating temperature the way it is now, although I haven't yet run it long enough, and I don't know whether it will set the temp alarm off, any suggestions.

Thanks Dancer905

 

[Bill Roosa]

check the wiring to the temperature sensor

The temp sensor is just a varable resistor. When you combine metal, electricity and salt water you get corrosion and that adds resistance to the circuit. higher resistances read as higher temps so I'd say you have a corroded connection somewhere in the circuit.
Try pulling the temp sensor wires off and cleaning them first as the easiest thing to start on.

99.44% of all electrical problems on a boat are corroded connections

 

[seadaddler]

Awhile

It should take a few minutes before the gauge starts reading a warm temp.

 

[Bill Roosa]

Also

The overheat sensor switch and the temp gage sensor are two compleatly different sensors and two different circuits. The overheat sensor is an on/off bimetal switch that just turns on the buzzer and light when it gets to a specific temp. The temp gage is a Thermistor (temperature verering resistor) that continusly veries in resistance with changing temp.

 

[Alan]

Bill is almost certainly correct. The temp gauge sensor is probably experiencing a high resistance due to corrosion which would push the reading on the gauge higher than it should. If you put an ohm meter between the sensor wire on the gauge and engine ground you will probably see a high reading. After cleaning the connection at the sensor and/or gauge the ohm reading should drop.