215 is not too hot and 220 is certainly not overheating.
The optimal perfect temperature to operate the engine in a perfect world is 212 degrees. The safe engine coolant temperature is around 250 degrees. It is perfectly fine and wont hurt anything at or below 250 degrees. Just above 250 degrees is where metal starts warping so above 250 its not wise to operate an engine. In all of my cobra tunes I shut the engine off when coolant temp reaches 244 degrees for safety. I have had several hundred people (myself included) hit the over-heat protection limit when cooling fans failed and it saved the engine. Never once had an engine failure.
Flushing the coolant system depends on how dirty the coolant currently is. If its still green basically drain the coolant and fill it with water. Get it up to operating temp and shut it off and let it cool enough to safely drain the cooling system again. Fill it up with water again and run her to operating temp. Repeat until the water coming out is as clean as it is when you put it in.
If the coolant is rusted then you will have to remove the thermostat and run the hose through it with the engine running until it comes out clear and repeat the method mentioned just above.
The eec-v pcm in your car does not support an oil temp sensor. The value your logging is completely bogus.
We did a test run today. 245 max coolant. First 5 minutes it was doing good but them after that it was shooting up temps quick. We got back home and felt the right side of the radiator is cool, left side is hot. It's also leaking. So we're thinking radiator is clogged.