Is my faststrike running hot?

1992 Johnson 150 Faststrike
Previous problem: ran too cold, thermostats were stuck open
repaired by disassembling and cleaning them, tested them in pan, all okay

New problem: temp gauge says hot (in red), but no overheat alarm. Discharge water is warm and top of head feels hot. I pulled thermostats and they were open, I could blow through them until they cooled down. I ran motor with thermostat cover off and plenty of water came out (to verify water flow).

Question: What temp should the motor be at? What is the best way (tool) to use to verify the head temp? I think I may have an inaccurate temp sender.

Thanks for any input,
Rustyhook

Use an infrared temp gun. The tops of the cylinder heads should be around 140° F plus or minus 15 degrees at idle. At higher speeds it will run cooler as the water pressure pushes the thermostats off the seats.