Coolant water pipe connecting the return hose to the engine block - one of several small coolant pipes in the M52/M54 cooling circuit that become brittle and prone to splitting, swelling or cracking after years of heat cycling. A common cause of a slow coolant leak that's easy to overlook until it fails outright.

Fitment: BMW E39 (525i/528i/530i), E46 (323/325/328/330 Ci/i), Z3 and Z4 - M52/M54 engines.