Antifreeze, often referred to as engine coolant, is a water-based liquid that circulates through an engine to regulate temperature. Antifreeze can freeze, but only when it is improperly mixed or when temperatures drop to extreme lows well below the freezing point of pure water. The protective quality of this mixture depends entirely on the concentration of chemical additives, typically ethylene or propylene glycol, combined with water. Maintaining the correct mixture is essential for safeguarding a vehicle’s cooling system against cold weather damage.
The Science of Lowering Temperature
Antifreeze works by exploiting a chemical principle known as freezing point depression. Water molecules naturally align into a rigid, crystalline structure when the temperature reaches 32°F (0°C), which is the process of freezing. When glycol is added, the molecules physically interfere with the water molecules’ ability to bond and form ice crystals.
This disruption forces the liquid mixture to reach a much colder temperature before crystallization can occur. The greater the concentration of dissolved particles, the greater this disruptive effect, leading to a lower freezing point. This property also raises the boiling point of the coolant, protecting the engine from overheating.
The Importance of Proper Mixing
The temperature at which the coolant mixture freezes is determined by the ratio of antifreeze to water. Automotive manufacturers commonly recommend a 50/50 mixture of concentrated antifreeze and water, which provides freeze protection down to around -34°F (-37°C). This ratio is standard because it balances freeze protection, boil-over protection, and heat transfer efficiency.
Adding too much water dilutes the glycol, causing the mixture to freeze at a higher temperature. Conversely, using too much pure, concentrated antifreeze is detrimental. Undiluted glycol has a relatively high freezing point of about 9°F (-13°C) and is less efficient at transferring heat. The concentration that provides the lowest possible freezing point is often near a 60% antifreeze to 40% water ratio.
Checking Your Level of Protection
To confirm the coolant provides adequate cold-weather protection, the concentration of glycol must be measured. The most common tool for this check is a hydrometer, which measures the specific gravity, or density, of the coolant. Some hydrometers use small floating discs to indicate the protection level, while others use a needle on a calibrated scale.
A more accurate method involves using a refractometer, which is the industry standard for testing coolant concentration. This device measures the liquid’s refractive index, which directly correlates to the percentage of glycol present. A small sample is placed on a prism and viewed through an eyepiece, where a scale provides a direct reading of the freeze protection temperature. Performing this check annually, especially before winter, ensures the mixture is within the safe range.
The Damage Caused by Freezing
The consequences of frozen engine coolant can be severe due to water expansion. Unlike most liquids, water expands by about nine percent in volume when it turns into solid ice. When this expansion occurs inside the rigid, confined spaces of an engine block, the immense pressure generated can cause catastrophic damage.
The most serious outcome is a cracked engine block or cylinder head, which typically results in an extremely expensive and time-consuming repair. The force of the expanding ice can also rupture the radiator, burst coolant hoses, and damage the water pump. Even if the engine is equipped with freeze plugs, the blockage of cooling passages by ice will immediately lead to severe overheating once the engine is started.