Coolant

Coolant (Coolant / Antifreeze Coolant) refers to the circulating fluid medium filled into the engine cooling system, typically formulated by blending deionised water, antifreeze (ethylene glycol or propylene glycol), and a dedicated additive package containing anti-corrosion, anti-rust, and anti-foaming agents in specific ratios. Its primary function is not only to efficiently absorb and dissipate heat during high-temperature engine operation—preventing overheating issues such as engine "boiling over" or cylinder scoring—but also to serve the crucial dual purpose of preventing cooling hoses and the engine block from freeze-cracking in sub-zero climates, while inhibiting electrochemical corrosion on metal components within the cooling system.

Core Technical Architecture and Operating Principles

An automotive cooling system operates via the forced circulation and thermal heat exchange of coolant within a closed loop:

Cooling Circuit Switching and Thermostat Regulation (Large/Small Circuit Switching and Thermostat Control): 

Coolant circulates through a closed loop comprising the engine water jackets, water pump, radiator, and thermostat. During a cold start, the thermostat remains shut so that engine oil and the cylinder block can rapidly reach optimum operating temperature, restricting coolant flow to an internal "small circuit" (bypass circulation). Once the coolant temperature surpasses a preset threshold (typically between 80°C and 95°C), the thermostat opens automatically, directing coolant through the front radiator to dissipate heat rapidly via oncoming airflow and the radiator cooling fan. 

Multi-Functional Additives and Anti-Boil/Anti-Corrosion Technology (Multi-Functional Additives and Anti-Boiling/Anti-Corrosion Tech): 

High-grade coolant not only offers an ultra-low freezing point (down to below -40°C), but its boiling point also typically exceeds 110°C to 120°C. Furthermore, advanced additive packages (such as Organic Acid Technology, or OAT) form a microscopic, dense protective chemical film over aluminium alloy, cast iron, and copper surfaces inside the engine. This prevents water jackets and cooling passages from oxidising, rusting, or suffering electrolytic corrosion from prolonged fluid contact, ensuring long-term reliability of the entire cooling system across several years or tens of thousands of kilometres.

Safety Guidelines and Operating Precautions 

Never Open the Radiator Cap or Coolant Expansion Tank Cap When the Engine Is Hot (Prohibiting Opening Coolant Caps While the Engine Is Hot):

Under normal operating conditions, the cooling system is highly pressurised (typically between 1.1 and 1.5 bar) with coolant temperatures well exceeding 100°C. Opening the cap on a hot engine is strictly prohibited; instantaneous depressurisation causes the superheated coolant to flash-boil and erupt violently from the filler neck, posing an extreme risk of catastrophic, deep scald injuries to the face and hands. Always allow the engine to cool down completely before inspecting or opening the system.

Do Not Mix Different Coolant Brands, Formulations (e.g. OAT vs. IAT), or Colours, and Avoid Long-Term Use of Water as a Substitute (Prohibiting Mixing Incompatible Coolants or Using Plain Water Long-Term):

Mixing coolants with incompatible chemical formulations can trigger adverse reactions, producing flocculent sludge, gel precipitates, or corrosive acidic compounds that clog narrow radiator cores and corrode the engine block. Indiscriminate mixing or using water as a permanent substitute must be strictly avoided; running purely on tap water drastically lowers the boiling point—leading to frequent overheating—while promoting severe limescale build-up and metal corrosion. When topping up or flushing the coolant, always adhere strictly to the manufacturer-specified grade and specifications outlined in the vehicle owner's manual.