You probably have a coolant fan switch that is reading too hot. Off the top of my head its either a one wire sensor with a green wire going to it. Or its a 2 wire sensor by the thermostat housing with a yellow and a brown wire going to it. You can find out for sure by asking your part store for a cooling fan switch. Very cheap money. If its not that then your cooling fan relay is stuck on, also very cheap money, good luck.