Foreign object damage occurs when a foreign object strikes either the compressor wheel or turbine wheel of the turbocharger. The most common foreign object damage occurs when a foreign object is introduced into the turbocharger air intake system between the air filter element and turbocharger compressor inlet where it can be drawn into the compressor wheel.

In automotive applications, foreign objects may include nuts, bolts, clips, pieces of rubber hose or even small stones that cause considerable compressor wheel damage as shown in Figure 1.

Foreign object damage may also occur if the air filter element is not installed properly in the air filter housing allowing the turbo to draw unfiltered air from around the element. This type of foreign object damage produces slow erosion of the compressor wheel as “dirty air” is pumped through the turbo and into the engine. Since the engine is also receiving the dirty air, engine symptoms such as excess crankcase breather pressure (“blow-by”) and oil consumption frequently accompany this type of foreign object damage shown in Figure 2. If the foreign object is not removed and the vehicle continues to be driven, the turbocharger compressor wheel will eventually look like the one shown in Figure 3.

Foreign object damage to the turbine wheel occurs when foreign objects exit the engine exhaust ports and strike the turbine wheel. Foreign objects that produce turbine damage include pieces of piston, piston ring, injector nozzles, engines valves or valve seats as well as apex seals in rotary engine applications. Figure 4 shows several “foreign objects” found in a turbocharger turbine housing.

Foreign object damage to the turbine wheel as shown in Figure 5 will result in poor turbocharger performance and significant turbine imbalance that, if uncorrected, will ultimately result in catastrophic turbocharger failure.

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