[C320-list] Engine water temp problem

[Graeme Clark]

First time I run the engine this year the water temp gauge goes off the clock!
I therefore bought a point and shoot laser thermometer and sure enough the engine temp ( measured where the sensor is and also at fuel injector points) is around 170f whereas gauge is showing 280-290f

So it's the sensor or the gauge. How do I test the sensor.  There is only a single terminal so I'm guessing the resistance changes with temp. Does anyone know what resistance should be at say, 170f ?

Or is there a simple way to test gauge

I did have the instrument panel out this winter to repair the lid so it could be a dodgy connection I guess. I'll check everything again but any more info would be handy as I'm stuck on boat with limited internet access!

Graeme
#366, 1996 running Yanmar 3GM30F


Sent from mobile: please excuse typos etc.!