my 1991 taurus sho temp.gauge fluctuates, has new thermostat and radiator on 1991 Ford Taurus

it hasn't actually overheated yet, but the temp gauge will get pretty high but drop back down. sounds to me like thermostat but it has already been replaced. not sure if the fan is kicking on or not i haven't driven it over 4 miles yet.water pump maybe?

Asked by for the 1991 Ford Taurus
most likely the pump. check belt for wear. may be warn.