The symptoms you've described lead me to think you've got air trapped in your coolant.

The fix is easy... when the motor is dead cold, take off the radiator cap and turn on the engine. Also, set your cabin heater temp to full hot, but leave the cabin fan off.

Let the car warm up while parked until the radiator fans come on.
You'll see some bubbles surface once the thermostat has opened up and the water pump circulates all the coolant in the system.