What Causes Water to Overflow from the Car Radiator?
2 Answers
Water overflowing from the car radiator is caused by the engine shutting down under high load or not using antifreeze. Below are the detailed reasons and solutions: Engine shutting down under high load: The cooling water pump, radiator fan, etc., stop running, preventing heat dissipation. Only the water around the cylinder block is used to dissipate the heat from the cylinder block. A sudden high-load shutdown causes water to overflow from the diesel engine radiator. Solution: Wait for the heat to dissipate before opening the radiator cap. Not using antifreeze: If this situation occurs during short-term driving, using tap water will cause scale buildup in the radiator and various pipes, leading to poor coolant circulation. This results in severe air trapping in the radiator when the water pump stops working, and prolonged use can damage the engine. Solution: Remove scale buildup from the radiator, repeatedly flush the pipes with clean water, check the seals of rubber pipes and interface clamps, and then add antifreeze with cleaning properties.
Having driven for so many years, I've seen quite a few cases of coolant overflow from the radiator. The most common cause is an overheated engine—when the temperature rises, the pressure increases, and the coolant spills out. This could be due to a broken fan that doesn't spin, a faulty water pump causing poor circulation, or issues with the radiator cap's seal, like it not being tightened properly or the pressure relief valve failing. Another possibility is overfilling the coolant; thermal expansion can cause it to overflow. I've encountered this situation before and had to quickly check the fluid level to ensure it didn't exceed the MAX line. Additionally, clogged pipes or leaks, such as from scale buildup or aging gaskets, require regular descaling. More seriously, if the cylinder head or engine oil mixes into the cooling system, the pressure becomes even more unstable. My advice is to first stop the car and let the engine cool down—don't keep driving to avoid high-temperature damage. Then, check if the fan is spinning and feel if the radiator is too hot. If simple fixes don't work, take it to a professional repair shop. Safety first to prevent burning out more components.
