Car Coolant: Do You Really Know How to Use It?

Coolant is an indispensable part of a car's engine, circulating within the engine cooling system to carry away excess heat generated during operation, ensuring the engine runs at its normal operating temperature. When coolant is insufficient, it can cause the engine's water temperature to rise excessively, leading to damage to engine components.

Coolant level inspection method

The correct method to check the coolant level is: open the engine hood, locate the coolant expansion tank, and inspect the coolant level, which should normally be between the MAX and MIN marks. If the coolant is found to be insufficient, the owner should promptly top it up. However, coolant should not be added indiscriminately, as besides its cooling function, it must also possess various properties such as antifreeze, anticorrosion, and scale prevention.

Coolant quality standards

China currently implements the SH0521-1999 standard for "Ethylene Glycol-Based Engine Coolant and Its Concentrate," which is formulated with reference to the ASTM D3306 standard. The products are categorized into two types: concentrate and coolant. The coolant is further classified into six grades based on freezing points: -25, -30, -35, -40, -45, and -50.

Industrialized countries have established corresponding quality standards and evaluation methods, such as the American standard for aluminum cylinder block testing (ASTM D3306) and the standard for cast iron wet cylinder liner testing (ASTM D4985), as well as the Japan Association of Corrosion Control standard (JACC).

Main Technical Indicators

The main technical indicators specified in the antifreeze standard include:

• Freeze resistance (freezing point):Ordinary antifreeze can reach -40°C, while high-quality antifreeze can achieve around -60°C.
• Boiling point:The boiling point of water is 100°C, and antifreeze should reach at least 108°C or higher.
• Metal corrosivity:Prevent corrosion of engine metal components
• Foaming property:Control the foaming characteristics of the coolant.
• Pump cavitation corrosion:Protect the water pump from cavitation corrosion
• Sedimentability (ash content):Control impurity content
• Solubility:Ensure good solubility
• Density:Standard density range
• Acidity value (pH value):Maintain appropriate pH levels
• Reserve alkalinity:The ability to buffer acidic substances
• Color change property:Color stability index

Coolant mixing ratio

Coolant is prepared by mixing antifreeze with water in a certain proportion. Automobile manufacturers usually specify the antifreeze mixing ratio for different low-temperature antifreeze grades in the user manual, and also designate the type of antifreeze, which cannot be mixed.

Under normal circumstances:

• When the ratio of antifreeze to water is 40:60, the coolant boiling point is 106°C and the freezing point is -26°C.
• At a 50:50 ratio, the coolant has a boiling point of 108°C and a freezing point of -38°C.

The general requirement is to prepare the coolant at approximately 5°C below the local minimum temperature.

Freezing Point and Concentration Detection

To test the quality of antifreeze, the most direct method is to check its freezing point and boiling point. The lower the freezing point and the higher the boiling point, the greater the temperature difference, indicating better quality. Conversely, the smaller the temperature difference, the relatively poorer the quality of the antifreeze.

Testing the freezing point requires the use of a specialized tester. The operation method of the freezing point tester is as follows: lift the cover plate and wipe the surface of the cover plate and prism clean with a soft flannel cloth; then use a pipette to drop the liquid to be tested onto the prism surface for measurement.

Modern engines' requirements for coolant

With the improvement of engine structure and advancements in material technology, modern automotive engines operate at higher temperatures, with normal working temperature limits generally exceeding 100°C. Taking domestically produced cars as an example:

• Shanghai Santana: 90℃～105℃
• FAW Jetta: 85°C～115°C
• Fukang: 90℃～118℃

If fully filled with water, the engine will boil when the temperature reaches 100°C. Additionally, water is corrosive and can form scale, affecting cooling efficiency. Therefore, a specialized coolant—antifreeze—must be used.

Usage Precautions

Antifreeze is important in any climate, not just in cold regions.

2. By lowering the freezing point and raising the boiling point of the coolant, antifreeze expands the engine's operating temperature range.

3. The main component of antifreeze currently on the market is ethylene glycol, which features a high boiling point and low freezing point.

4. The antifreeze also contains additives to prevent ethylene glycol oxidation, prevent corrosion, and inhibit foam formation.

5. Antifreeze of different brands and models cannot be mixed; the specified model should be used as required by the manufacturer.

Through scientific testing methods and stringent quality standards, it ensures that the coolant provides reliable protection for the engine, extends its service life, and enhances the safety and economy of vehicle operation.