One other question, have you ever cleaned the outside of the radiator? The passages where air needs to flow through can get clogged up with dirt, little bits of tire rubber from the track, etc., not to mention if you ride in the rain you will get a dirt buildup on the surface. Even if you get all the air out of the system internally if the radiator can't efficiently transfer the heat you will have a problem. I clean mine at least once or twice a year, best way is off the bike that way you can hold it up to a light and examine it for blockage in the fins. Use a good aluminum safe cleaner and soak it down good and then rinse like crazy. You'll never get all of it out but you can remove quite a bit of it.
That's a good idea. Kawasaki has me capping the drain before I fill, but I fill it tediously slow to prevent air getting stuck. I'll have to try your method next time.
Has anyone suggested the temp sensor? could the temps actually be fine, but the sensor is bad and giving faulty readings??