Problem with water temp gauge

[Bad buoy]

My 2004 2500 has a problem where gauge reads about 10 degrees hotter than the engine
My boatyard tested and showed me the tester side by side with gauge
I removed the gauge and sent back to manufacturer had it rebuilt
The new one has the same problem
My boatyard replaced the sending unit from engine same problem
A tech at my boatyard says he worked for searay dealer for years and this was a notorious problem
Have not seen anyone post a thread on this so wondering if my problem is special
I'm about to bring the boat to searay bay liner dealer for annual service
I am expecting them to suggest a new gauge set for the boat since my maxum style gauge is no longer available
Thanks

[Huddo007]

This is a very long shot but I had the same problem with my bayliner capri, I used to get an engine overheat alarm at various times as well, I replaced thermostats, water pumps, impellors, gauges the list goes on, finally and only through a fluke I noticed that when I put my nav lights on the temp would raise 10-15 on the gauge (but no change in water temp), perhaps try switching your accessories on one at a time paying close attension to your temp and see if you are getting a false back feed

[ss3964spd]

You can also remove the sending unit and the gauge and send both in to the gauge repair place. They should be able to calibrate the gauge to the sending unit.

[shrew]

Take a look at your volatge guage. Try turning of everything 12V (GPS, Radar, Fridge, stereo, etc.) Take a look at the volt meter. See if it raises. If it does, look at the temp. guage. See if the temp. guages drops as the volt meter rises. Vice Versa, as you power things on, see if the volt meter drops. If it does, do the temp. guage rise?

[boilerbob1]

Any chance that some new wiring was installed that may be a source of signal noise?

There may not be a problem, the thermostat is set for a specific temperature (mine is 175) and the sensor is downstream and system is cooling down some before I get my reading. I have a plastic card with my start-up checklist and the expected gauge values and just keep track of things like that. I act only if there is a deviation. I always get a temperature drop when I leave the Mississippi River and go play up in the Apostle Islands (Lake Superior).