I had the same experience. I was also told by most that the problem was a bad head gasket or cracked block.
One solution offered, however, was that the water pump was moving too much water. I remembered that with my old, original pump that I didn't have the problem. One fix was to reduce the size of the water pump vanes. Another was to install a thermostat in the upper radiator hose to slow the flow.
I installed the t-stat. No more puking out the cap. I now can fill the radiator until I can just start to see coolant above the plate. When the car warms up, the level rises in the top tank but never to the overflow outlet. Been that way for over a year now.
It's a cheap fix...if it works for you.
