Overheating

New radiator, new thermostat. The car never shows hot. It will overheat in the coolant reservoir and shoot into the overflow where it boils and will push it to the radiator (I can hear it). Since the radiator is full, it shoots it back into the overflow, then back to the reservoir that has the fill/cold. It is almost as if the thermostat is sticking. There is no whitish color in the oil fill or on the dip stick. It does not blow white smoke. The dashboard temperature gauge never shows it hot even when it is boiling underneath. I also have heat so it cannot be the heater core. Please help.