Temp gauge Mercruiser 3.0 not working

[johnt_mn]

I have a 2007 Bayliner 175 with Mercruiser 3.0 TKS. My engine water temperature gauge has stopped working, needle just shows the minimum value, 100 degrees all the time. I grounded the sender wire at the engine and the gauge deflected to fully pegged. I thought this meant the gauge was good so I replaced the sending unit sensor. This didn't fix the problem. Then I replaced the gauge, still not working. Any ideas? Might it be a thermostat problem? The housing around the thermostat doesn't seem to get very hot while running. The engine seems to run fine, even at WOT.

 

[itsathepete]

Do you know if there is actually have a thermostat in there? Gauges, especially at lower temps are not terribly accurate. They are pretty much designed to be "close" at the operating temp and are more of a guide. Put an IR temp gun on the engine block, thermostat housing and exhaust manifolds while running to tell for sure

 

[johnt_mn]

Do you know if there is actually have a thermostat in there? Gauges, especially at lower temps are not terribly accurate. They are pretty much designed to be "close" at the operating temp and are more of a guide. Put an IR temp gun on the engine block, thermostat housing and exhaust manifolds while running to tell for sure

I'll check the IR reading when I get home, but I do know that in the past the temp gauge has always shown around 175 degrees (needle straight up) while running. Currently it never budges from 100 which is the lowest value on the gauge.

 

[itsathepete]

So I assume there is actually a thermostat in place. A thermostat can fail in the open position which could be the problem.

 

[johnt_mn]

So I assume there is actually a thermostat in place. A thermostat can fail in the open position which could be the problem.

This sounds most likely, I'm going to check that next time I get up to the cabin. Thanks!