Whenever a turbocharger receives inadequate lubrication, the results are almost always catastrophic. Causes of inadequate lubrication include failed engine oil pump drive, low engine oil level that causes the oil pump pickup to be momentarily uncovered, foreign material lodged in the turbocharger center housing oil feed passage(s), or a restricted turbo oil feed line. When the oil supply to the turbocharger is restricted, the hydraulic pressure necessary to maintain lubricating oil between moving parts is removed and metal to metal contact results.

A turbocharger that has been subjected to a restricted oil supply usually exhibits one or more of the following: a bent or broken shaft, bearing surfaces with metal transfer from one bearing surface to the other (typically bronze bearing material is transferred or “smeared” on the corresponding steel bearing surface), and “blueing” of the bearing surfaces resulting from the heat produced by the metal to metal contact. Turbocharger bearing surfaces that have been damaged from inadequate lubrication are shown in the figure below.

A restricted turbo oil feed line is often difficult to diagnose especially if each end of the line appears normal. However, it is possible for the feed line to be restricted at some point in the center of the line where visual inspection alone is not sufficient. In automotive gasoline turbocharger applications where the turbo oil feed line is routed close to or clamped to significant heat sources such as the engine exhaust manifold or turbocharger turbine housing, significant layers of coked engine oil can be deposited inside the feed line over time to the point that the turbocharger fails from a restricted oil supply. An example of a turbo oil feed line “plugged” in the middle is shown in the figure below.

Whenever a turbocharger fails catastrophically, it is prudent to thoroughly inspect all components of the turbocharger oil feed to prevent damage to the rebuilt or replacement unit. When in doubt, replace the turbo oil feed line with a new line that has been thoroughly cleaned before installation.

NEXT - 4.0 TURBO OIL DRAIN/ENGINE BREATHER CONSIDERATIONS