Congratulations on your "new to you" coach. I know you will enjoy it. I suspect you have a Cummins ISC 8.3L engine. Good engine.
At 220º F you are running a little higher than I would expect. Could be the sender or a poor ground connection. But may be a lot simpler.
You have a rear radiator and a lot of "stuff - dirt, oil, etc.) gets pumped thru it. Just the nature of the beast. Unless you know different, figure that the prior owner never cleaned the radiator. Not hard to do.
Put some "Dawn" liquid dish soap in a spray bottle, open the rear doors covering your radiator and spray the heck out of the entire radiator fins. Let it stand for about 15 minutes and then flush the entire surface with lots of water. DO NOT use a pressure washer. You could damage the fins. The average hose sprayer can generate enough pressure to force any accumulated crud out of the fins after the "Dawn" has loosened it up. Don't be afraid to repeat the operation a second time.
If you try the cleaning, please let us know if it lowers your operating temp.
Green lights and soft breezes,
Roland, Diane & Katie - the furry 4-footed kid
'01 Diplomat - ISC330 - Allison MD3060 - Progressive Ind. EMS-50C - Hughes Autoformer - '06 Jeep Liberty CRD