Greetings sailors - C36 #2164 MkII  2003 model year:
.  My engine temp gage has been showing 180 deg when cruising.  I've tried and tried to find the cause. 1) Removed the HX  Heat Exchanger boiled out, repainted. Replaced, checked hoses, replaced two.
2) checked the raw water thru hull for clogs.
3) replaced the thru hull to strainer hose
4) check the raw water strainer
5) replaced the thermostat
6) replaced the temp sending unit, checked to make sure the elect connection was intact
7) changed the raw water pump (finally) to an Oberdorfer
​8) even bought one of those cool infared temp gages, read about 160 deg at the thermostat after warming up to running temp.  Odd I thought.
​Still the gage reads 180 deg!
I decided to boil a pan of water, insert the removed temp sending unit (with connection and ground) into the pan of water with a digital thermometer   With the ignition on (engine nor running of course), and as the water slowly cooled in the pan with the sending unit, my wife read off the helm gage.  I compared to my digital readings of the cooling water in the pan.
Results:  The temp gage was reading 20 deg too high!
Before I replace the temp gage and a calibrated sending unit, I want to ask this group if temp gages can be adjusted.  Thinking the back side may have an adjustment screw?  Thoughts?