BMW 840i xDrive Gran Coupe 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.

Oil lines for the turbocharger, along with the coolant lines, if equipped, are the only line of defense for the turbocharger, so it is essential that any leak from the turbocharger or its supply and return lines is corrected immediately. Turbocharger failure is expensive and the symptoms mentioned will develop quickly once oil supply is reduced.

These lines do leak, but they are assembled with high torque fittings, copper or brass seals, and reinforced with steel braids on the exterior of the high density rubber lines. This means that failure is less common than it could be, but expect at least one leak or line failure at some point in the vehicle's service life. This is due to the high heat endured by the oil lines throughout normal operation.

Oil leaks are commonly diagnosed by locating the source of the leak visually. If the source is unclear, the area covered by oil can be degreased, and the oil can have a ultra-violet light reactive dye poured in to detect the leak with a blacklight (UV light). This is an easy way to ensure the leak is accurately identified, but normally not necessary. Blockage will be detected by either pressure testing the lines as the engine is cranked, not started, or by removing the return line to note lack of oil presence. Clogs are much less common, and would likely go unnoticed during diagnosis for quite some time.

Oil lines for the turbocharger CHRA will be removed by disconnecting the banjo bolts securing the ends of the oil lines to the engine block and oil pan, removing the old metallic washers, and removing any fasteners which may prevent the oil line from moving during operation. Installation involves leaning all mating surfaces, replacing the metal washers, replacing banjo bolt, and torquing the fasteners to specification. After installation, the engine will be ran to ensure all leaks have stopped.

Oil line upgrades are available, especially for aftermarket applications. Unless the system requires an upgrade, the factory oil supply and return lines should be used since they will likely last the remainder of the vehicle's service life. In fact, many aftermarket components in the price range of the factory oil lines will likely be of lower quality.

The banjo bolts and seals used on the oil lines for turbochargers are installed under high torque for the size of fastener used, as well as the material used. This makes torquing these fasteners worrisome for the inexperienced mechanic, and for good reason. Over Torquing is extremely easy to do, and a highly accurate torque wrench should be used.

Aside from torquing the lines, this is not a difficult job, but it comes with much uncertainty and a high risk to reward ratio. If performed incorrectly, the oil lines can leak out the engine oil at a fast rate, provide low oil pressure to the turbocharger, and destroy the turbocharger. It is best that this repair be left to a professional, especially since it typically is not a costly repair.