2003 Nissan Sentra Car overheating sometimes

Hi my 2003 nissan sentra is overheating sometimes. It only does it when I drive for more than 30 miles or so though. The other day I drove it about 50 miles before it overheated then I let the car sit over night and the next day I drove another 50 miles but it didnt overheat at all and just wondering if its a temp gauge or a water pump. Im really hoping its not a gasket but I don't have and oil in the coolant or any leakage and I have heat as well and I heard thats a way to see if the gasket is bad. Thanks