I'm not certain, but it's
possible that the fans are kicking on
because the temperature has spiked. I think it's
possible that you don't see that until after the fans kick on becasue the ECU and the water temp gauge use different sensors.
Or there's a better answer. I don't know. I'd still replace the thermostat before looking at anything else. It'll give you a chance to drain and refill your coolant anyway.
