Posted on 10/31/2025
The radiator cap might seem like a small, simple part, but it is critical in keeping your engine cool. It’s responsible for maintaining pressure in the cooling system, preventing coolant from boiling, and helping coolant flow between the radiator and the overflow tank. When it starts to fail, your car may show symptoms that are easy to miss at first but can lead to overheating or coolant loss if ignored. What the Radiator Cap Actually Does Your car's cooling system operates under pressure to raise the boiling point of the coolant. The radiator cap is designed to hold that pressure, usually between 13 and 16 pounds per square inch, depending on the vehicle. When pressure builds to the set limit, the cap allows a small amount of coolant to flow into the overflow reservoir. As the system cools down, a vacuum forms. The radiator cap has a second valve that opens to allow coolant to flow back into the radiator from the reservoir. This process helps maintain pro ... read more