This occurs when air gets trapped in a part of the engine making it hard for coolant to flow. To eliminate this the engine's cooling system needs to be bled of air when coolant is added. Top off the radiator or reservoir and let the engine run until the thermostat opens. Air should bubble out. Add fluid until it stops.
Well you need to first make sure that you don't have a leak letting air into your system. Then you need to do a good system bleed. Making sure to fill the system to the correct level and checking to make sure it stays there. The might also me kits available to help force air out of the system.