* Air in the cooling system. Air in the cooling system can cause the radiator overflow to bubble because the air bubbles rise to the top of the system and escape through the overflow. This can happen when the cooling system is refilled or when there is a leak in the system.
* A faulty radiator cap. The radiator cap is designed to maintain a certain amount of pressure in the cooling system. If the radiator cap is faulty or not sealing properly, it can allow air to enter the system and cause the radiator overflow to bubble.
* A head gasket leak. A head gasket leak can allow exhaust gases to enter the cooling system, which can cause the radiator overflow to bubble and the car to overheat.
* A cracked or damaged radiator. A cracked or damaged radiator can allow coolant to leak out of the system, which can also cause the radiator overflow to bubble.
If you are experiencing this issue, it is important to have your car inspected by a qualified mechanic to diagnose the problem and make the necessary repairs.
