1. Impact damage

Impact damage caused by a foreign object entered into the turbine or cast iron housing is clearly visible on the rotor or compressor wheel. Impact damage in the cold part may be varied, for example, damage caused by the unwinding of the lock nut (this type of damage most often occurs in case of oil lack, then the rotor is twisted while compressing blade continues to rotate). And damage caused by fine dust and sand or non- solid objects.

In the last few years manufacturers focus on producing titanium compressor wheels, because titanium has much greater strength and endurance compared to aluminum. It is important ports for fresh air feed to the turbine and ports for exhaust gases discharge out of the turbine to be checked carefully for foreign objects.

Never try to repair the blades as they will damage again. 
Never continue driving with a turbocharger with defect blades as the balance of the impeller will be disturbed.

2. Contaminated oil

Solid particles scratch the rotor, sleeves as well as the inner hole of the housing. Contaminated, old or wrong oil also results in slow damage of the turbocharger. Often oil begins to char more at much lower temperature than normal. Carbon starts to deposit on the bearing housing surface and internal grooves and on the thrust bearing which sooner or later stops optimal lubrication and damage the turbocharger.

To avoid this damage, oil and filter must be of good quality and changed when changing to a new turbocharger and at regular intervals depending on the vehicle and the specific motor

Damage from solid particles may be a result from: а) clogged, damaged or poor quality oil filter
b) dirt penetrated during repair
c) engine wear or debris from manufacturing
d) oil filter valve faulty groove 
e) poor quality of oil leads to charring

3. Interruption of oil flow

It is important to know that in the normal state the rotor can produce more than 250 000 revolutions, and the distance between the static elements is filled by oil film with a thickness of about 0.01 - 0.08 mm. Interruption of the oil flow at repeated short periods (4 to 5 sec.) causes overheating and polishing the turbocharger sleeve surface.

This is usually a result of failure in the oil supply system or:
а) replacing the turbocharger without filling the lubrication system
b) oil and filter replacement
c) long periods of non operation
d) incorrect ignition procedure especially in freezing temperatures
e) low oil pressure due to failure in the lubrication system
f) contamination of oil
g) operation with over-tilted engine

4. Lack of oil

Critical shortage of oil for long periods (8-10 sec.) will influence the turbocharger system. The rotor is most vulnerable to direct contacts metal to metal, (yellow-brown-blue) shades may be seen on the rotor itself. The flinger and thrust bearing are affected as well.

Lack of oil is more dangerous than interruption of oil flow and may be a result from:
а) broken or choked oil feeding pipe
b) oil pump damage
c) little or no oil in the oil tray
d) long engine use loosens the lubrication system
e) lubrication system sweeps air

5. Overheating and overloading

As a result of excessive high temperatures or turning off the engine without cooling period, the turbocharger is covered with carbon deposits. Running of the engine at idle speed for 2-3 min is recommended prior turning off to cool the turbocharger. The turbine absorbs heat in the iron (which often leads to cracks in the cast iron housing) and this causes the system oil coking. Often carbon deposits are accumulated in insulated cap. The main damage occurred on the shaft ring and slots. Oil flows out and clogs the cavity, resulting in distortion and deformation of the opening.

Reasons:
а) clogged air filter
b) the engine is turn off in operating mode
c) poor quality of oil
d) irregular oil changing
e) leakage of fresh air and exhaust gas
f) faulty oil pump
g) incorrect turbine assembly
h) insufficient oil flow 

Each turbocharger is designed according to the maximum speed and load it can bear. They depend on the engine characteristics, air intake, pressure, flow and temperature of the exhaust gases. Therefore, the manufacturers' recommendations in this regard are the turbocharger numbering to be strictly followed during replacement. Overloading problems are destructive both in the cold and in the warm part of the turbocharger.