1998 8.3 diesel water temp

I had the same thing happen to me two weeks ago, pulled over radiator was not boiled over took temp readings with my IR gun heads were 157 thermostat housing was 190 not 280. Removed connection to temp probe in head, reinstalled it off and on several times to remove any corrosion still read 280 and occasionally drop back to 190. Drove to the CG shut engine off but temp gauge still read 280. Several hrs later once engine cooled turned key on and temp still read in red zone. Next morning all was well again drove home and it read fine. My probe was a single wire probe so I figured the ground was through the treads so I tightened it slightly and it worked fine on last weeks trip. You can check the ground with a multi meter set to ohms from the sensor to the engine block for continuity and clean the wire connection first to see if that fixes your problem.