The engine coolant is usually changed every two years or every 40000 kilometers of driving. However, this cycle may vary depending on the vehicle's usage, the quality of the coolant, and the manufacturer's recommendations. For example, for vehicles that run for a long time, such as taxis, it may be necessary to change the coolant more frequently.

　　If the engine coolant is not replaced in a timely manner, the following effects may occur:

　　Coolant failure: Expired coolant may contain impurities, causing the internal chemical composition to fail and lose its original effectiveness, thereby affecting the cooling effect.

　　Decreased cooling effect: If the coolant is not replaced for a long time, the evaporation of internal water will change the freezing point of the coolant, reduce the cooling effect of the coolant, and may cause the engine to overheat.

　　Corrosion of metal parts: The chemical composition in the coolant can prevent rusting and corrosion of metal parts in the engine cooling system. If the coolant is not replaced, the anti-corrosion agent will gradually fail, which may cause corrosion of the metal components inside the cooling system, thereby shortening the service life of the car.

　　Increased maintenance costs: Long term failure to replace the coolant may lead to internal problems in the engine cooling system, thereby increasing the cost of car maintenance. For example, overheating of the engine may cause damage to the cylinder head, requiring the replacement of expensive parts and extensive repair work.

　　Risk of icing: In winter, if the freezing point of the coolant is insufficient, icing may occur, which may damage the engine cooling system.

　　Therefore, in order to maintain the normal operation of the engine and extend the service life of the car, it is recommended that car owners regularly replace the engine coolant according to the vehicle manufacturer's recommendations or the general cycle mentioned above. At the same time, when replacing the coolant, attention should be paid to selecting high-quality coolant suitable for the vehicle and following the correct replacement steps and precautions.