The best way to drain the system is at its lowest point, in the smart's case they
have actually installed a coolant drain plug that can be removed with an allen key.
It is located on the back of the engine. Lay down under the back of the
car and you'll see it just above and to the right of the oil filter housing.
With the engine cold, undo the coolant drain plug. Remember to put a container underneath it to
catch the old coolant. Access the coolant expansion tank by following
As soon as you take it off, the coolant will quickly drain from the engine.
The petrol uses 4.2 litres and the diesel uses 4.5 litres of mixed coolant.
Topping Up The Coolant