I agree, it sounds like you have air in your cooling system. I was having this same problem with my rear radiator setup.
This is what I did to get the air out of the system, not that you have to be this through. You could skip 1 and just fill the radiator up and go to 2.
1. Removed the thermostat housing and thermostat, and fill the block from the intake. Once the block fills up the water will overflow into the radiator and start to fill it. Once the block overflows, or the radiator, put the thermostat and housing back on. Then top off your radiator.
2. Start up the engine and let it warm up. Watch the coolant / water level. Once it reaches the thermostat temp of 180, you'll see the coolant start to flow and a little steam / water vapor will start to come out. Top it off again and put the radiator cap on.