Cooling system problem

I have a 2006 Ford Mustang V6. Recently after driving and turning the car off the coolant has been spilling out through the cap of the coolant reservoir. The car drives fine and does not overheat so it appears the cooling system works while driving. I have not identified any visible leaks and the heat inside the car works. I have replaced the coolant reservoir cap, thermostat, and thermostat casing. Does anyone have suggestions or an idea of what is happening. Thanks.

If anyone overfilled the coolant reservoir, this is normal,

I am not sure about your car, but on some the radiator fans should run after the engine is shut off. I remember in Canada stopping off at a station, I had the same problem, and they said a lot of cars do that. I guess a cool down drive before you shut off the engine might be one suggestion.

I had this symptom once.
The radiator cap wasn’t holding pressure.

Coolant reservoir wasn’t overfilled. New radiator cap was purchased and still had the same problem. Fan runs appropriately.