Should coolant be added when the engine is cold or hot?
2 Answers
It is generally more appropriate to add coolant when the engine is cold. This is because the coolant pressure is high when the engine is hot, and opening the cap may cause the coolant to spray out, which can easily scald people. Methods for selecting coolant: The basic indicators of coolant are the freezing point and boiling point. On the market, coolants come in several specifications with freezing points of -15°C, -25°C, -30°C, -40°C, etc. Generally, it is advisable to choose a coolant with a freezing point at least 10°C lower than the lowest temperature in your region. Methods to determine if coolant is low: Observe the coolant warning light on the dashboard. If it lights up, it is likely due to low coolant, though it could also be caused by excessively high cylinder temperatures. Check the coolant reservoir. If the fluid level is below the minimum mark (MIN), do not continue driving; add coolant promptly. Check the water level scale on the coolant tank. The normal coolant level should be between the maximum and minimum marks. Whether the coolant is low depends on the scale. If the coolant is below the minimum mark, it indicates a shortage of coolant.
This is a question I often get asked myself: you must always add coolant when the engine is cold. I've encountered several instances where novice car owners unscrewed the radiator cap while the engine was still scalding hot, resulting in boiling liquid spraying out and burning their arms. When the engine is hot, the cooling system is under extremely high pressure, with temperatures exceeding 90 degrees Celsius—equivalent to a pressure cooker. Forcibly opening the cap is particularly dangerous, and thermal expansion can also lead to misjudging the fluid level. I usually wait about 2 hours after parking, ensuring the coolant has completely cooled down, before slowly unscrewing the cap to check. Remember to check the MIN and MAX marks on the reservoir tank and avoid exceeding the upper limit. Regularly replacing the coolant is also crucial, as degraded fluid can corrode the pipes and affect engine cooling. I recommend a thorough inspection before each winter to avoid breakdowns and freezing on the road.
