This radiator coolant overflow bottle expansion tank comes with a cap and is designed for use in specific vehicle models including E32 735i, 530i, 535i, 540i, and 740iL.It matches OEM part numbers 17111712196 and 17111719110.The unit is built to withstand typical under-hood conditions, including exposure to heat and automotive cooling system chemicals, and supports consistent cooling system performance by helping maintain appropriate fluid levels and pressure.