The Genuine BMW Engine Coolant Temperature Sensor O-Ring - 61311361249 is a small circular rubber ring that is used to seal the connection between the engine coolant temperature sensor and the engine block. It is a genuine OEM part made by BMW and is designed to fit perfectly and provide a reliable seal. This O-ring is an essential component for maintaining the proper functioning of the engine cooling system, as it prevents coolant from leaking out and ensures accurate temperature readings. It is compatible with various BMW models and is a crucial part for ensuring the smooth operation of the engine.