Radiator boiling over continually

So, I got my motor started on the dyno stand and the radiator was full of water. It boiled over 3 times. I was told to do this a time or two so the thermostat would kick on, however a 4th time I added an antifreeze mix and it boiled over once again. Before I continue with running the motor I want to ask, is this an indicator of something gone wrong or broken? If not, how do I get the motor to stop boiling over like this.




Thanks