What Are the Symptoms of a Faulty Car Radiator Cap?
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When the car radiator cap is damaged, coolant will spray out from the radiator cap, reducing the flow of coolant into the engine and lowering the pressure. The heat generated by the engine cannot be carried away by the coolant, leading to engine overheating or even boiling. Here are the relevant details: How the Car Radiator Cap Works: The car radiator cap consists of two layers, with a valve core in the middle. The valve core is equipped with a spring and blocks the filler neck. There is a passage above the valve core connected to the overflow tank. When the radiator pressure is high, the water pressure lifts the valve core, allowing coolant to flow into the overflow tank. The valve core also includes a one-way valve. When the radiator is low on coolant, the one-way valve opens, allowing coolant from the overflow tank to refill the radiator. Functions of the Radiator Cap: (1) Sealing. Under any operating condition, the radiator cap must prevent coolant from leaking out. (2) When the coolant temperature rises and the radiator pressure increases to a certain level, the radiator cap automatically opens the pressure relief valve, allowing excess coolant to flow into the auxiliary tank due to thermal expansion. (3) When the coolant temperature drops, the radiator forms a vacuum due to the coolant's contraction. The radiator cap automatically opens the return valve, allowing the supplementary coolant from the auxiliary tank to flow back into the radiator.
A broken radiator cap is no small matter. I've seen many cars break down because of this issue. The first symptom is coolant leakage. When you open the hood, you'll notice water stains or discolored liquid leaking from the radiator neck—a sign that it can't hold pressure. The second is engine overheating. When the radiator cap fails, the system loses pressure, disrupting coolant circulation. The temperature gauge will spike into the red zone, and you may feel the engine struggling, hear the fan running at full speed, or even see smoke. The third symptom is coolant boiling over while driving, accompanied by gurgling sounds or steam escaping from the engine bay. It may also cause hard starts or unusual vibrations. The root cause is often a worn-out cap or damaged seal, leading to pressure system failure. At best, it wastes fuel; at worst, it damages the engine. Get it fixed immediately—don't delay. Regular checks of the cap's seal and pressure rating are crucial.
