Can You Add Water to a Car's Coolant?

[StAlexa]

You cannot add water to a car's coolant. Adding water to the coolant will lower the boiling point of the new coolant mixture, which may cause the car to overheat. The main component of coolant is ethylene glycol, which has excellent thermal stability—preventing freezing in winter to protect the engine from cold damage and cooling the engine in summer to ensure it operates at an optimal temperature year-round. This is an effect that cannot be achieved with water alone. Typically, coolant has a freezing point of -25°C. However, after adding water, the new antifreeze mixture's freezing point rises to around -10°C, which in many cold regions can cause the antifreeze to "freeze," severely damaging the radiator or cooling system.