My problem: coolant flowing out of the overflow tube.

I put in a new thermostat and new thermostat gasket. I filled the block with coolant first. I topped off the radiator, but not too full.
Here's what happens now. I started the engine from cold. I walked back and forth from the open radiator cap to the temp gauge. As soon as the temp gauge showed warm, I looked down the radiator and could see when the thermostat opened 'cause the coolant rose up within the radiator and into the overflow tube.
Does this indicate a blockage somewhere?

Tips and comments please?


"Happiness equals reality minus expectations" - Tom Magliozzi