[L1] 1 Overview [L2] 1) Definition [L4] - A medium that lowers the heat of the engine (and related parts, radiator, etc., the target object) to remove thermal deformation and adverse effects. [L4] - Role of lowering the melting point (freezing point) of the coolant to prevent it from freezing in winter. [L4] - Also called Antifreeze. [L4] - Generally uses Ethylene Glycol as a major component, adding additives to improve cooling performance and rust prevention. [L5] * Based on Mono-Ethylene Glycol (MEG) (approx. 93 vol.%), followed by adding corrosion inhibitors (5~7 wt.%). [L5] * Additives include silicate stabilizers, anti-foaming agents, denaturants, lubricants (for heater valve lubrication), and dyes. [L5] * Used by mixing with soft water. [L2] 2) Types of Coolant (Antifreeze) [L3] ① Ethylene Glycol [L4] - Ethylene Glycol: Chemical formula C2H4(OH)2, a type of alcohol, the simplest compound among dihydric alcohols. [L4] - Physical Properties of Ethylene Glycol [L5] a. Phase: Liquid (Colorless) [L5] b. Molecular Weight: 62.07 g/mol [L5] c. Melting Point: 260K (-14℃) [L5] d. Boiling Point: 470K (197℃) [L5] e. Density: 1.1155 kg/m^3 [L4] - Safety of Ethylene Glycol [L5] a. Ingestion: Damage to liver, kidneys, central nervous system. [L5] b. Inhalation: Irritates airways. [L5] c. Skin: Can be absorbed through skin. [L5] d. Eyes: Irritating. [L3] ② Propylene Glycol [L4] - Propylene Glycol: Chemical formula HOCH(CH3)CH2OH [L4] - Less toxic than Ethylene Glycol. [L4] - Generally, antifreeze labeled as non-toxic to coolant often contains Propylene Glycol components. [L2] 3) Mixed Water [L4] - Mixing Ethylene Glycol with water raises the boiling point in proportion to the amount of Ethylene Glycol. [L5] * Since the freezing temperature of pure Ethylene Glycol is only -12℃, the freezing temperature (freezing point) of the liquid mixed with Ethylene Glycol and water varies depending on the mixing ratio. [L4] - Mixing with water interferes with the hydrogen bonding of Ethylene Glycol, lowering the freezing point. [L5] * The freezing point of a liquid mixed with 70% Ethylene Glycol and 30% water is up to about -50℃, but antifreeze with a 1:1 ratio of water and Ethylene Glycol is about -35~40℃. [L4] - Compared to the boiling point of water, the average operating temperature of engine parts is relatively very high, so the application of coolant is absolute. [L5] * Piston temperature is about 260℃, exhaust valve is about 650℃, and cylinder liner coolant side temperature is about 120℃. Since this temperature range can boil water, the use of coolant is necessary. [L1] 2 Management of Coolant [L2] 1) Replacement of Coolant [L4] - The replacement cycle of coolant is generally 2 years, but the timing may vary depending on the contamination status. [L4] - When replacing, must check the type of existing antifreeze and ensure antifreeze of the same series is injected. [L5] * Injecting antifreeze of a different series may react with existing antifreeze to generate suspended solids and clog cooling lines. [L2] 2) Mixed Water Management [L4] - Mixed water (antifreeze) is a flammable substance, so it must never be handled near fire. [L4] - If the engine is overheated, inject after the engine cools down. [L4] - Using distilled water is recommended when diluting antifreeze. [L5] * Natural water contains mineral components (Calcium, Magnesium), which act as foreign substances in the engine or radiator system, causing problems. [L5] * Use tap water when distilled water is unavailable.