This can cause the coolant overflow tank to, well, overflow or … sounds as if the coolant is boiling. Radiator Caps Illustration. The coolant may very well indeed be boiling, and it could be a direct = result of a bad coolant reservoir cap. Signs of a Faulty Radiator Pressure Cap. valve on mine went bad and it would boil, pressurize and then finally = A pool of leaking coolant You can easily tell that there is a leaking coolant when there's a clear fluid leaking from underneath your car along the area where the radiator is located. Fuel inefficiency. 3. Are you familiar with all of the different parts that are in your car’s cooling system? went bad and it would boil, pressurize and then finally leak out of the = The leak only happens when the car is ON. OBD1 edition? If the radiator cap is stuck, pressure may build inside of the radiator, which could … When there is a problem with the radiator cap, the coolant may go to the reservoir without the normal trigger of excess pressure. It has been used so widely that it can’t get any major modifications in every car. The radiator cap helps raise the boiling point of coolant, prevents air from entering the system and ensures the pressurised cooling system in your car runs smoothly. 3 Answers. October 27, 2020 by Tom Harbid. A radiator caps primary function in a cooling system is to retain the engine´s cooling system pressure. This = My >temperate gauge registers normal =