Q&A

 Journeyman

It may caused by a bad sensor in the coolant reservoir that tells the computer its low on coolant, this is easily replaced and isn't very expensive either, most people ignore it , but i think it's better to keep the system working good , just in case it really get low, it will keep you from ruining a good engine by running it hot, some of these sensors are also located around the thermostat housing.

Good luck and best regards!