- The impeller and turbine wheel can strike the turbocharger housing on account of bearing damage (Fig. 1). This can be discerned from wear marks on the housing (Fig. 2).
- If the turbocharger boost pressure is too low, the engine will not perform properly: the rotating assembly no longer reaches the maximum speed and can no longer build up the full boost pressure as a result. The reason for this is the mixed friction caused by the inadequate lubrication.
- The exhaust system emits black smoke. These are the effects of the engine not being supplied with enough air and a correspondingly too rich fuel-air mixture.
- The shaft shank exhibits clear discoloration (Fig. 3), which arises from friction and the resultant high temperatures between the shaft and the bearings. The cause of this is inadequate lubrication. If the temperature exceeds a certain level, the bearing material will become deposited on the shaft (Fig. 4) or the bushing might even become completely fused to the shaft.
- A broken shaft shank (Fig. 5) is the result of operating the turbocharger for a prolonged time without enough oil. The shaft material can thus burn out and break.
- If bushings that are permanently incorporated in the bearing housing become fused to the shaft, the bushings might turn out of position in the bearing housing (Fig. 6).
- The shaft might suddenly become blocked in the bearing housing due to the mixed friction. If the rotating assembly is suddenly blocked, the locking nut of the impeller can become loose.
- The rotating assembly can exhibit a large imbalance owing to the contact with the housing, which might result in the radial bearing breaking (Fig. 7).
- Due to incorrect oil or heat soak, the bearing housing can become carbonized.
- The radial bearings have fretted.
- The axial bearing exhibits fretting marks or carbon deposits.
-  Knocked-out bearings can cause too great a wobble of the shaft, whereby the bearing collar might also be damaged.



-  If the maintenance intervals are exceeded, the oil filter can no longer filter enough dirt out of the oil. In this case, the dirt particles penetrate through the open bypass valve of the oil filter into the engine circuit.
-   If the engine is operated with a blocked oil filter, the small abrasive particles cannot be filtered out of the oil.
-   If the cylinder head gasket or the oil cooler is leaking, water will enter the oil circuit and dilute the oil. Its carrying capacity is thus reduced.
-  If the engine was repaired, but not properly cleaned before assembly, dirt will be in the engine even before putting it into operation for the first time.
-  The charge air cooler was not replaced. Accumulated engine oil, chippings, or fragments from the prior damage usually find their way into the engine with a time delay.
-   If the engine is subject to considerable wear, the mostly metallic wear debris also finds its way into the turbocharger via the oil circuit.
-  If combustion faults occur in the engine, non-combusted fuel can end up in the oil. The carrying capacity of the oil is reduced by this dilution.



-The maintenance intervals according to the manufacturer's recommendations should always be complied with.
- Only high-quality oil filters specified for the respective vehicle should be installed.
- Only engine oils specified by the vehicle or engine manufacturer may be used.
- A new charge air cooler and air filter should always be installed when replacing the turbocharger. In addition, an oil change including oil filter replacement must be carried out.
- The air filter housing and charge air line should be cleaned by suction.