Coolant level is more accurate when the engine is cold. Coolant, fully known as antifreeze coolant, is designed to prevent freezing. It protects the radiator from cracking and the engine cylinder block from freezing damage during cold seasons when the vehicle is parked. Antifreeze is not just for winter use; it should be used year-round. In standard vehicle maintenance, the engine coolant should be replaced every year. Coolant consists of three components: water, antifreeze, and additives. Depending on the antifreeze component, it can be classified into alcohol-based, glycerol-based, ethylene glycol-based, and other types of coolant. If the coolant level is at the lower limit when the engine is cold and in the middle when hot, this indicates insufficient coolant. Generally, the adequacy of coolant is determined when the engine is cold. Normally, the coolant level should be between the upper and lower limits. Therefore, if the coolant level is at the lower limit when the engine is cold, there is an issue, and coolant should be added immediately. When the engine heats up, the coolant level rises because the engine temperature increases, causing the coolant to expand and the level to rise. Typically, coolant is stored in the main reservoir and the overflow tank. The overflow tank should only be filled halfway or up to the maximum mark to accommodate the expanding coolant when the engine is hot. If the overflow tank is completely full, it cannot hold the expanding coolant when the engine is hot, leading to overflow and loss of some coolant. If a small amount of coolant needs to be added, it can be poured into the overflow tank. However, if there is no coolant in the main reservoir, it should be added directly to the main reservoir, as adding it through the overflow tank would be slower.
