What Type of Antifreeze & Coolant for Smart Roadster. How Much Recommended antifreeze for radiators of Smart Roadster. Find out how much coolant does your car need. Car A Rac presents recommended by manufacturers types for all popular vehicles. Replacing the coolant - FQ101 The Roadster engines take 4.2 litres of pre-mixed coolant. Unlike for the engine oil, smart have very kindly provided a drain-off point for the coolant. You can find this just above the oil filter on the engine block. Ensure that the car is parked level.