This part is a Coolant Reservoir Cap, a physical component made for specific Hyundai and Kia vehicles: Hyundai 2015-2016 Genesis G80, 2017-2020 G90, 2015-2019 Sonata, 2019-2024 Nexo; and Kia 2017-2020 Cadenza, 2019-2020 K900, 2016-2020 Optima. It is a direct replacement for the original cap with part numbers 25441-B1000 and 25441B1000, designed to fit the coolant reservoir opening of these vehicles.​ The only function of this cap is to physically seal the coolant reservoir. By doing so, it helps maintain the reservoir's internal pressure, which prevents the coolant (a liquid used to cool the engine) from leaking out while the vehicle is running. This is a purely mechanical action, with no connection to chemicals, treatments, or biological processes.​ Installing this cap requires no tools—just turn it clockwise on the reservoir until it fits tightly. It is made to replace worn or damaged original caps, ensuring the reservoir stays closed during vehicle operation.​ This product is exclusively a vehicle part. It is not a pesticide, nor does it contain, use, or relate to pesticides, pest control, bacteria/mold treatments, or any chemical agents. It is engineered solely for use in automotive coolant systems to perform the physical task of sealing the reservoir.​