Major Causes of Damage:
Most turbocharger damage can be traced to one of a few basic causes:

Lubrication Related Problems
Foreign Object Damage
Operational Temperature Extremes
Material and Workmanship

Careful examination of the parts from a damaged turbocharger and proper interpretation of their condition will usually pinpoint the cause of a unit�s problem. If a turbocharger is ruined by an external fault and that fault is not found and corrected, the replacement unit will soon fail in the same way as the original. The photographs used in this section illustrate the damage to parts typically found when a turbocharger has failed due to one of the basic causes listed above. Although your parts may look slightly different than those shown, the evidence of failure remains the same.

Lubrication Related Problems:
Insufficient Lubrication
Lack of proper lubrication can ruin a turbocharger within mere seconds of operation. With shaft rotation speeds approaching 200,000 rpm in some models, all bearings must receive a supply of oil that can stabilize, lubricate and cool. When lubrication is slowed, stopped or interrupted for any reason, metal to metal contact first occurs at the journal bearings/shaft journals/bearing bores of the center housing. Without the oil, friction will generate enough heat to turn the shaft and/or thrust collar blue (See Picture 1). (This bluing is often not as evident in units with liquid-cooled center housings.) The thrust bearing, thrust collar and/or backplate mating surface will also show signs of damage. Once the bearings are damaged, "shaft motion" increases. Instead of rotating in a perfect circular motion, the shaft begins to orbit. As bearing clearances are enlarged, shaft motion becomes more intense, and damage accumulates. The center housing seal bores, shaft hubs, and thrust components (thrust collar, thrust spacer, and backplate assembly/thrust bearing, as applicable) are damaged next. This additional damage, in turn, allows for more violent shaft motion. After shaft motion reaches a certain point, the turbine and compressor wheels will contact their respective housings damaging the blades and possibly backing off the shaft nut. When blades are damaged by housing rub, the precise balance of the wheel/rotating assembly is destroyed, leading to even more shaft motion. The shaft may eventually break from a combination of motion stress, fatigue and destabilization (due to the original problem, insufficient lubrication).

Foreign Material In Oil:
Foreign material in the oil includes various sizes of abrasive particles, corrosive chemical compounds, and dilution by coolant or fuel. Foreign material in the engine lubrication system first damages the journal and thrust bearings. When foreign material in the oil is found to be the primary cause of damage, steps should be taken to identify the foreign material or eliminate its entry into the system.

Abrasive Particles:
Fine abrasive contaminants will score and wear virtually every bearing surface(See Picture 2). If material particles are large enough, the contaminate related damage is more confined to journal bearing outside diameters and center housing bearing bores because centrifugal force keeps the contaminants away from the spinning shaft.

Corrosive Chemicals;
Corrosive chemical compounds alter surface finishes and clearances. When surface finishes are too rough, oil films are penetrated allowing metal to metal contact.

Diluted Oil;
Diluted oil has its film strengths reduced and does not easily adhere to surfaces. The lack of surface adherence does not allow the shaft to be dampened and supported by its encompassing oil film.

Sludged Center Housing:
Even premium oil will decompose if temperatures are forced high enough during operation or shutdown. When these temperatures reach the center housing the deposits will form throughout its interior. (See Picture 3) As deposits accumulate, oil passages become restricted which reduces oil flow through the unit, further elevating the temperatures aggravating the condition. The granular carbon deposits, now part of the oil supply to the bearings, damages surfaces and increases clearances or accumulates on the bearing surfaces diminishing space for oil films to develop. All of these deposits alter the bearing system and prevent normal operation. Excessive bearing damage from foreign material in the oil will eventually lead to shaft motion and, finally, turbocharger failure.

Other lubrication problems - low oil pressure, wrong oil grade or oil not changed often enough, will eventually affect the turbocharger bearings as previously described.

Foreign Object Damage:
When a foreign object enters the compressor or turbine the turbocharger will become affected very quickly. Upon close inspection you�ll find that the damage can often be related to the type of material. Hard objects, such as bolts, valves or rocks, will break pieces from the blades or "machine" them down.(See Picture 4) Abrasive matter, such as sand or dirt, will wear-away the undersides of the blades and their edges. Soft material, such as shop rags, will bend the compressor wheel blades backwards.(See Picture 5) Any wheel blade damage can destroy the balance of the rotating assembly, which leads to shaft motion, loss of efficiency or noisy operation. When foreign objects strike the wheel, loads can be extreme. The loads can be high enough that catastrophic failures result. Foreign object damage to the compressor wheel distributes damage relatively even to all blade edges. (See Pictures 4 & 5) Foreign object damage to the turbine wheel distributes damage evenly to all blade tips. (See Picture 6) After a foreign object has entered the turbocharger, be sure to check the engine for initial or resultant damage. And remember, if a unit has failed because a foreign object has entered the system, damage occurs first at the wheels and then spreads to the center housing and bearings.

Operational Temperature Extremes:
Turbocharger damage can be caused by high temperatures during operation or after shutdown. Some types of damage has been discussed in the sludged center housing section. Generally, the source of heat that causes the problem comes from the exhaust gases. Elevated exhaust temperatures can come from incorrect engine air/fuel ratios, timing problems, restricted exhaust systems, malfunctioning exhaust oxygen sensor, or other engine control system problems.

Excessive exhaust temperatures can damage the turboc