I haven't seen these cars to work on yet, but you should be able to bleed air out of the system. if the radiator has a cap, take it off while cold, start the car, turn heat on, let air run out of the system, fill radiator as necessary, close the radiator cap. Basically you want water to overflow from the radiator. But maybe these cars only have a radiator cap on the reservoir...

Air in the system causes overheating problems.