BMW 740i Turbocharger Oil Line Replacement Cost

Turbochargers are like all other rotating assemblies in that they develop quite a bit of friction and heat as they spin. This is especially true for turbochargers since they spin up to 300,000 times per minute. Something moving this fast, as light as it is, creates extremely high forces as it spins, so it must be protected by oil. Lucky for the turbocharger, the engine that it is mounted to is an excellent source of oil, and that oil is carried from the engine to the turbocharger via the turbocharger oil line.

The turbocharger oil line, even on stock vehicles, is often a steel-braid reinforced rubber line that can withstand far greater pressures than it will ever need. The oil supply line runs oil pressurized by the engine oil pump from the engine block to the turbocharger central housing (CHRA). The central housing rotating assembly will take this pressurized oil, allow it to be squished through the compressor shaft and bushing/bearing, and sends it back through the other side of the CHRA. From there, the oil return line will let the used oil drain from the CHRA oil outlet into the oil pan of the engine.

Blockage and leaks are the only possible issues for the turbocharger oil lines, and these are characterized in one of two ways. In either case, the turbocharger speed sensor, if equipped, will register slower speeds for the turbocharger compressor wheel/turbine. This is because lack of lubrication has slowed the wheel significantly due to friction. Also, the engine may register an underboost condition as the turbocharger is not spinning fast enough to create the pressure required of it. The check engine light will illuminate, and OBD trouble codes will be stored referencing these issues. Finally, the turbocharger will stop running once heat and friction cause internal damage, and the engine will either stall from an excessively rich air to fuel mixture, or it will run extremely poorly, roughly, and weakly.