Genuine OEM Mini Water Pump Thermostat O-Ring Seal, part number 11518613804. This O-ring is essential for creating a watertight seal between the water pump and thermostat housing, or other cooling system components, preventing coolant leaks. It is made from a high-temperature, coolant-resistant rubber compound. Genuine OEM O-rings are manufactured to precise dimensions and material specifications, ensuring a reliable and leak-free seal for your vehicle's cooling system, which is critical for preventing engine overheating.