Can Water Be Added to Coolant?
2 Answers
Coolant can have a small amount of distilled water added, but tap water should not be used as it is particularly prone to forming scale, which can easily clog pipes. Adding water to antifreeze will raise its freezing point. Normally, antifreeze has a freezing point of -25°C, but if diluted with water, the freezing point can increase by about 10°C. In such cases, driving to colder areas may cause the antifreeze to freeze, potentially damaging the radiator and water tank. An imbalance in the additive ratio of antifreeze reduces its effectiveness, making it more susceptible to scale formation and radiator corrosion. In severe cases, leakage may occur.
Adding water to the coolant as a temporary fix is passable, but I wouldn't recommend doing it long-term. Once during a long trip when I noticed the fluid level was too low, I topped it up with some purified water just to get home. Within two months, the radiator was full of rust, and the mechanic said minerals in tap water can cause scaling that clogs the cooling fins. Factory coolant contains multiple additives—not just for antifreeze protection but also to prevent corrosion of rubber hoses. If you keep cutting corners by adding water, the water pump's sealing ring can become brittle and leak, and the engine might even suffer cylinder scoring from overheating. In a pinch, distilled water is acceptable if you're out of coolant, but you must flush and replace it entirely once you're home. It's best to always keep a bottle of the OEM-specified coolant on hand for top-ups—it'll save you from costly engine overhauls down the road.
