What is the reason for water backflow when the engine temperature is not high?
2 Answers
The reasons for water backflow when the engine temperature is not high include: 1. The cylinder head is uneven, and the tightening torque of the cylinder head bolts is insufficient; 2. The bolts used have been stretched and deformed, failing to compress the cylinder gasket properly; 3. There are defects such as sand holes or cavitation in the water passages adjacent to the combustion chamber in the cylinder block or cylinder head, causing leakage; 4. Sudden addition of cold water when the temperature is too high causes the water passages in the cylinder block or cylinder head to crack due to thermal shock, allowing high-pressure gas to enter the water passages. The normal water temperature of an engine is between 80°C and 90°C. Both excessively high and low temperatures are abnormal and detrimental to the engine's normal operation. To ensure the engine operates within the optimal temperature range, the vehicle is equipped with a cooling system to enhance engine power, reduce engine wear, and minimize fuel consumption.
That time when I was driving long-distance, I also encountered the issue of coolant overflowing despite the engine temperature not being high. The temperature gauge was perfectly normal, showing no signs of overheating, but after parking, I found the expansion tank bubbling and spilling liquid, leaving the engine bay all wet. I did some research myself and suspected it might be a faulty water pump causing poor circulation and liquid buildup leading to backflow. Or perhaps air had entered the system, creating uneven pressure that forced the coolant out. Later, when I took it to a mechanic, it turned out the radiator cap had aged and lost its seal—replacing it fixed the problem. It’s quite annoying when issues like this happen without high temperatures, as it indicates hidden flaws in the system that haven’t fully failed yet. I suggest fellow car owners regularly check coolant levels and not wait until a breakdown occurs to act. If you encounter a similar situation, stay calm—first inspect basic components like hose connections, then seek professional help to prevent minor issues from escalating into major damage.
