* Freezing: Water expands when it freezes, potentially cracking engine blocks and hoses. This is a major problem in colder climates.
* Boiling: Water boils at a relatively low temperature (100°C or 212°F). At higher operating temperatures, it can cause overheating and damage to the engine.
* Corrosion: Water can corrode engine components over time, leading to premature wear and failure.
* Lack of Lubricity: Modern coolants contain additives that provide lubrication to the water pump. Water alone lacks this protection.
* Scale buildup: Water can leave mineral deposits (scale) inside the cooling system, reducing its efficiency.
Therefore, while pure water *can* be used in a pinch (e.g., as a temporary emergency measure), it's highly recommended to use a proper engine coolant (antifreeze) which is a mixture of water and antifreeze chemicals designed to address these issues. These chemicals raise the boiling point, lower the freezing point, inhibit corrosion, and provide lubrication.
