Connecting the upper radiator to the top fitting on the engine (next to the oil filter housing). Over time, rubber hoses can become hard, with the internal walls covered in sediment and the plastic fittings turning brittle or the internal o-rings simply leaking. A must replace hose for any owner of an E70 X5 looking to preventively maintain or restore their cooling system. We've found these Rein hoses to be the best quality, which is manufactured by the original equipment supplier and use BMW Genuine plastic hose connectors.