I have a 02 CBR 600f4i, last year it was doing some weird thing where it was starting to overheat (240), it would also give weird readings like 190, 195, 170, 180, 200. I flushed the coolant, checked the spark plugs, tested the thermostat, changed the oil, and did a valve adjustment. There was an intake and exhaust valve that were badly out of spec, after the valve adjustment and replacing the battery, that died over the winter, and everything seemed to be working well all spring and some of the summer but it started doing the temperature fluctuations again. I was going to ignore it but after one ride it jumped from 220 to 255 after I turned the bike off. I'm almost ready to just take this to the dealer but I wanted to try here first.

 

change the thermostat with a new OEM one.

its cheap and easy.

also make sure all the air is out of the system.

Random fluctuations like this usually point to a thermostat sticking occasionally. It could be a bad water pump with a partially loose impeller, or a partially plugged rad, but that's harder to diagnose over the internet.

thermostats are cheap, and if you have any doubt, change it, especially if its out already.