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.

I had something similar in symptoms in 2012
But much worse results (cumins 6tb 5.6L )
The plastic expansion tank cracked and leaked
It was over heating from coolant loss,
The temp would go up, then coolant system pressure would release at the cap, temp would drop, then immediately start climbing
I ended up broke down, was towed too Flagstaff, and spent thousands of $$ in engine repairs, plus motel expenses for a ten day stay
Be careful, check everything

Could be either stuck thermostat OR bad sender unit/gauge.

Particularly if the indicated temperature changes rapidly under steady-state driving conditions, likely a sender unit/gauge. If so, start by verifying that the connection at the engine is clean and tight.

I'm not familiar with that coach and engine, but if it was a regular truck I'd say your cooling system thermostat is sticking.

yes it seems simple but have to make sure also does it have a idiot light

I have a 1998 Monaco with the same engine that did the same thing on the way to Baltimore. I pulled over and checked the water and could also see that it was not overheated I drove on checking it a couple of more times. Short solution was that either the sending unit or the gauge had failed. Replaced the sending unit and no change. My solution was to have the shop get a new gauge, sending unit, and run new wiring from the front to the back. Never another problem and even towing a heavy car trailer over Fancy Gap it never passed 190 degrees. Normally without the trailer it stays around 170. Hope this helps.

ok