Boiling coolant out of the overflow tank?

I have a boiling coolant issue. The temp needle does not go above operating temp despite coolant boiling out of the overflow tank.

I have replaced the rad cap, water pump, overflow tank cap, and thermostat. Initially the car did not have a thermostat in it. It was cut out/removed. A complete thermostat was now installed.

I have had this car for close to three years and I never had a problem until about a month ago.