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The only two things left are the actual thermostat sensor that tells you the digital read out and the water pump. If the water pump was bad, you bike would over heat and die. If it was the sensor, I would assume the read out would fluctuate all over the place.
Two things that could have happened...
1. There are air bubbles in the system: Bleed it by warming it up with the radiator cap off. Lightly squeeze the radiator hoses to loosen any bubbles while the bike is cool too.
2. The radiator is clogged: Might have been caused by hard water heating and cooling and depositing minerals in the system.
Thats all I got for you...