What is the reason for water leakage caused by the expansion tank cap not releasing pressure?
2 Answers
Failure of the radiator cap to release pressure can lead to abnormal operation of the radiator, affecting the engine's normal working performance. The radiator cap, also known as the pressure radiator cap, is installed on the car's radiator and is an important component of the vehicle's cooling system. The radiator cap is equipped with a valve that generates pressure, helping to maintain the engine at an effective temperature. Below is relevant information: Working principle: When the car is running, the temperature of the radiator increases, raising the pressure inside. When the pressure reaches a certain level, the pressure valve is pushed open by the pressure, allowing the coolant to flow into the adjacent overflow tank. When the car stops running, the cooling system draws the water back from the overflow tank. Precautions: Never fill the radiator with tap water, as prolonged use of tap water can cause rust or scale buildup in the radiator. This is a very common issue, as rust and scale can restrict the flow of antifreeze in the cooling system, reducing the radiator's heat dissipation performance and, in severe cases, damaging the engine.
Even a seasoned driver like me with over 20 years of experience has encountered this issue. The coolant reservoir cap failing to release pressure and causing leaks is primarily due to cap aging problems—such as weakened internal springs or deformed rubber seals blocking the vent hole, preventing pressure release. When the cooling system heats up, fluid expansion causes pressure to spike, forcing coolant to leak from radiator seams or rubber hoses. I remember one severe leak in my old car where the temperature gauge skyrocketed mid-drive, nearly causing a breakdown; replacing the cap finally solved it. I recommend regularly checking the cap’s condition by gently pressing to see if it vents properly, and cleaning the vent holes to prevent clogging. A new cap costs little—don’t wait until leaks damage the engine or fry the water pump, which isn’t worth the risk. Adopting this habit saves major repair costs and ensures peace of mind on the road.
