Hi there, the radiator will tend to warm up quickly, as the turbo is right behind it and thats getting hot straight away. If the thermostat was missing the car would take "longer" to warm up, as the water isn't being held in the head for a short period of time until the thermostat opens.

As for the lumpy running when warm, and steaming breather, think u need to do a bit of investigating, take the breathers off & pipes and flush and clean them if neccessary. It might be a bit of hot oil vapour coming out.