Putting only cold water in your car radiator is a temporary emergency fix, not a recommended long-term solution. While plain water transfers heat better than coolant alone, it lacks critical additives that protect your engine. In a pinch, if your car is overheating and coolant is unavailable, adding distilled water is acceptable to get you to a repair shop. However, you should flush the system and refill with the proper coolant mixture as soon as possible.
Using plain tap water regularly can cause significant damage. The minerals in tap water, like calcium and magnesium, lead to scale and rust buildup inside the radiator and engine block. This corrosion can clog the narrow cooling passages, reducing efficiency and potentially causing the engine to overheat. Furthermore, water has a higher freezing point and a lower boiling point than proper coolant. In cold climates, frozen water can crack your engine block, which is a catastrophic and expensive repair.
A proper coolant mixture, typically a 50/50 blend of antifreeze and distilled water, provides essential lubrication for the water pump and contains corrosion inhibitors. This mixture is engineered to withstand extreme temperatures, both hot and cold. For most climates, a 50/50 mix is ideal, but in areas with severe winters, a 60/40 antifreeze-to-water ratio might be recommended.
| Coolant Mixture | Freezing Point | Boiling Point (at 15 psi) | Primary Use Case |
|---|
| 100% Water | 32°F (0°C) | 212°F (100°C) | Emergency use only |
| 50/50 Mix | -34°F (-37°C) | 265°F (129°C) | Standard for most climates |
| 60/40 Mix | -62°F (-52°C) | 270°F (132°C) | Extreme cold weather |
| 70/30 Mix | -84°F (-64°C) | 276°F (136°C) | Maximum freeze protection |
The bottom line is to use water only in an absolute emergency. For routine maintenance, always use the manufacturer-recommended coolant pre-mixed or mix concentrate with distilled water.
