The Radiator Stop Leak is designed to stop leaks in a cooling circuit that can contain up to 10 liters of coolant. Adding a second bottle would therefore be useless. The Radiator Leak Stop is made of vegetable particles that can plug the holes that cause leaks up to 1.4 mm. If its action is not sufficient, this suggests that the holes are larger. It is therefore preferable to have the general condition of the circuit checked by a professional.