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Technical information
AFTERMARKET
 Table of contents

1 Preface 4

2 Inadequate lubrication 6

3 Contaminated oil 8

4 Oil leakage at turbocharger 10

5 Foreign object damage 12

6 Damage due to excessive exhaust tempe- 13

ratures
14
7 Overspeeding

2 | © MAHLE © MAHLE | 3
 1 Preface

MAHLE is one of the most important development partners and man-

ufacturers of engine components and systems as well as filter systems This brochure summarises typical damage scenarios and sheds light
Preface

Preface
in the automotive industry. The engineers at MAHLE develop products on their possible causes. The information is supplemented by tips on
of the highest quality throughout the world in conjunction with engine how to avoid such damage in the future.
and vehicle manufacturers. The same high quality guidelines are also
applied for the spare parts in the aftermarket. In this way, we aim to make it easier for repair shops and engine
reconditioners to troubleshoot potential damage causes and ensure
Inadequate lubrication

Inadequate lubrication
Numerous checks during and after production ensure the high quality appropriate engine repair, which in turn is necessary for the long and
level of MAHLE products. If failures occur in practical operation, the reliable functioning of our products and hence the entire engine.
causes are mostly found in the engine environment.

TURBOCHARGER—THE FUNCTION
Turbochargers are used to enhance the performance and optimise the
combustion. To achieve good and complete combustion in the engine,
a mixture ratio of 1 kg fuel and approximately 15 kg air is necessary
(stoichiometric fuel ratio). This air volume corresponds to about 11 m³.
During turbocharging, the density of the intake air is elevated and the
Contaminated oil

Contaminated oil
air volume increased.

The volumetric efficiency and thus the efficiency of the combustion

engine are significantly improved by means of turbocharging. In addi-
tion, the torque can be increased considerably, which in turn serves
to enhance the performance. The turbocharged engine with the same
power output as a naturally aspirated engine can therefore be designed
with a smaller displacement and hence lower weight (downsizing).
Oil leakage at

Oil leakage at
The core of the turbocharger is the rotating assembly, consisting of
turbocharger

turbocharger
the turbine wheel with shaft and impeller. The turbine wheel is located
on the exhaust side. It is firmly connected to the shaft, e.g. through
friction welding or laser welding. The impeller is mounted on the other
end of the rotor shaft, generally with a screw connection.

The exhaust flow from the engine is channelled through the turbine,
Foreign object damage

Foreign object damage

which leads to a rapid rotational movement of the turbine wheel, subse-
quently driving the impeller. The turbine speed depends on the design
and exhaust volume. In small turbochargers, the rotating assembly
reaches speeds of up to 300,000 rpm. In order not to destroy the
turbocharger and engine, the maximum charge air pressure is usually
limited by boost pressure regulation.
Damage due to excessive

Damage due to excessive

TURBOCHARGER REPLACEMENT: THIS IS WHAT
exhaust temperatures

exhaust temperatures
MATTERS
In terms of construction and function, a turbocharger is designed for
the service life of the engine. In practice, however, the high-perfor-
mance components in the exhaust gas system are subject to diverse
risk factors that can lead to premature failure.

The analysis and rectification of the cause of the failure are the prereq-
uisite for a successful repair. Otherwise, the new turbocharger might
fail again after a short period of time.
Overspeeding

Overspeeding
4 | © MAHLE © MAHLE | 5
 2 Inadequate lubrication

Inadequate lubrication is one of the most frequent causes for turbo- CAUSES
chargers to fail. If the turbocharger is not sufficiently supplied with oil,  T he oil level in the engine is generally too low. As a result, not only
Preface

Preface
damage will occur within a very short time. This is due to the very high the engine but also the turbocharger receives an inadequate oil
speeds of the turbocharger. lubrication and oil cooling.
 T he oil used is not sufficiently temperature-resistant, leading to
EFFECTS increased carbonisation. This might cause problems: the oil supply
 T
he impeller and turbine wheel can strike the turbocharger housing line of the turbocharger and the oil bores in the bearing housing of
Inadequate lubrication

Inadequate lubrication
on account of bearing damage (Fig. 1). This can be discerned from the turbocharger can become carbonised.
wear marks on the housing (Fig. 2).  If the engine was turned off while hot, the oil supply line can become
 
If the turbocharger boost pressure is too low, the engine will not carbonised, which means the turbocharger is no longer supplied
perform properly: the rotating assembly no longer reaches the with enough oil.
maximum speed and can no longer build up the full boost pressure  If the cold engine was brought to high speeds immediately after the
as a result. The reason for this is the mixed friction caused by the Fig. 1 Fig. 5 start, there is a risk that the oil supply in the turbocharger is not yet
Impeller after contact with housing Broken shaft shank
inadequate lubrication. sufficient and hence the oil film in the turbocharger tears off.
 T he exhaust system emits black smoke. These are the effects of the  If foreign substances make it in the oil circuit, such as dirt or sealing
engine not being supplied with enough air and a correspondingly residues, the oil supply line of the turbocharger and/or the bearing
too rich fuel-air mixture. housing of the turbocharger might be clogged.
Contaminated oil

Contaminated oil
 
The shaft shank exhibits clear discoloration (Fig. 3), which arises  
If the viscosity of the oil is too high, the oil transport to the bear-
from friction and the resultant high temperatures between the shaft ing points is delayed, which means that the timely oil supply of the
and the bearings. The cause of this is inadequate lubrication. If turbocharger is not ensured. At too low a viscosity, the carrying
the temperature exceeds a certain level, the bearing material will capacity of the oil is too low, which can lead to mixed friction.
become deposited on the shaft (Fig. 4) or the bushing might even  
If the engine is operated with biodiesel or vegetable oil, there is a
become completely fused to the shaft. risk of the engine oil gelling. This increases the viscosity of the oil
 
A broken shaft shank (Fig. 5) is the result of operating the turbo- and it can no longer be transported through the thin oil bores in the
charger for a prolonged time without enough oil. The shaft material turbocharger.
can thus burn out and break.  
The cross section of the bearing housing supply bore might be
Fig. 2
Oil leakage at

Oil leakage at
 If bushings that are permanently incorporated in the bearing housing reduced either through an incorrect flange seal or by a liquid sealant.
turbocharger

turbocharger
Contact marks in the compressor housing
become fused to the shaft, the bushings might turn out of position in
the bearing housing (Fig. 6). REMEDY/PREVENTION
 
The shaft might suddenly become blocked in the bearing hous- n The engine must be warmed up and cooled down.
ing due to the mixed friction. If the rotating assembly is suddenly  The engine must be supplied with enough oil.
blocked, the locking nut of the impeller can become loose.  O nly engine oils specified by the vehicle or engine manufacturer
 
The rotating assembly can exhibit a large imbalance owing to the may be used.
Foreign object damage

Foreign object damage

contact with the housing, which might result in the radial bearing n Only driving short distances should be avoided.
Fig. 6
breaking (Fig. 7). Twisted bushing  T he maintenance intervals according to the manufacturer's recom-
 D ue to incorrect oil or heat soak, the bearing housing can become mendations should always be complied with.
carbonised.  O nly high-quality oil filters specified for the respective vehicle should
 The radial bearings have fretted. be installed.
Fig. 3
 The axial bearing exhibits fretting marks or carbon deposits. Discoloration of the shaft shank  
The corresponding mounting kit for the turbocharger must always
 
K nocked-out bearings can cause too great a wobble of the shaft, be used.
Damage due to excessive

Damage due to excessive

whereby the bearing collar might also be damaged.  W hen operating the engine with biodiesel or vegetable oil, the ser-
exhaust temperatures

exhaust temperatures
vice intervals should at least be halved.

Fig. 4 Fig. 7
Bearing material fused onto the shaft Broken radial bearing
Overspeeding

Overspeeding
6 | © MAHLE © MAHLE | 7
 3 Contaminated oil

Dirt, soot, fuel, water, combustion residues, or metal abrasion can REMEDY/PREVENTION
contaminate the oil. Even the smallest particles in the oil can cause  T he maintenance intervals according to the manufacturer's recom-
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Preface
serious damage to the turbocharger due to its extremely high speeds. mendations should always be complied with.
 O nly high-quality oil filters specified for the respective vehicle should
EFFECTS Fig. 4 be installed.
Clear signs of wear on the shaft at the bearing point
 
The smallest foreign substances in the oil cause grooves in the  O nly engine oils specified by the vehicle or engine manufacturer
bushings (Fig. 1). The piston rings in the turbocharger can undergo may be used.
Inadequate lubrication

Inadequate lubrication
serious wear. As worn piston rings can no longer adequately seal  A new charge air cooler and air filter should always be installed when
the turbocharger, the oil enters the turbine side, which can be dis- replacing the turbocharger. In addition, an oil change including oil
cerned by increased oil consumption. filter replacement must be carried out.
 T he bearing play of the rotating assembly increases due to the worn  T he air filter housing and charge air line should be cleaned by
bushings. This leads to wobbling movements and causes the tur- suction.
bine wheel or impeller to come into contact with the housing (Fig. 2).
The shaft might subsequently break off.
 T he bearing collar, i.e. the thrust washer of the axial bearing, exhib- Fig. 1
Grooves in the radial bearing
its grooves.
 Grooves or fretting marks are discernible in the axial bearing.
Contaminated oil

Contaminated oil
 
Due to a blocked oil return line, the oil in the turbocharger can no
longer flow off and is instead forced out to the compressor and
turbine side. On the turbine side, the oil might then burn onto the
shaft and coke (Fig. 3). Owing to the oil carbon layer, the bearing
housing and the piston rings might be significantly worn off as a
consequence.
 T he shaft of the turbocharger shows clear signs of wear at the bear-
ing points (Fig. 4).
Oil leakage at

Oil leakage at
CAUSES
turbocharger

turbocharger
 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 pen-
etrate 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 Fig. 2
Turbine wheel after contact with housing
particles cannot be filtered out of the oil.
Foreign object damage

Foreign object damage

 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 assem-
bly, 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
Damage due to excessive

Damage due to excessive

into the engine with a time delay.
exhaust temperatures

exhaust temperatures
 
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 Fig. 3
Carbonised oil on the turbine side
end up in the oil. The carrying capacity of the oil is reduced by this
dilution.
Overspeeding

Overspeeding
8 | © MAHLE © MAHLE | 9
 4 Oil leakage at turbocharger

If the engine shows signs of increased oil consumption and emits

blue smoke, it is imperative that the turbocharger is included in the REMEDY/PREVENTION
Preface

Preface
cause analysis. Important: Oil is forced out of the housing from a tur-  T he engine must only be filled to the specified maximum oil level.
bocharger only if divergent operating conditions predominate in its  O nly engine oils specified by the vehicle or engine manufacturer
environment. may be used.
 T he oil return line must be routed exactly as in the original state. In
EFFECTS addition, it must be ensured that all heat shields are attached.
Inadequate lubrication

Inadequate lubrication
 Oil is forced out of the turbine or compressor side of the turbocharger.  
The oil return line and the connections to the crankcase must be
n Blue smoke is emitted from the exhaust system. checked for continuity. We generally recommend replacing the line
 
Engine oil has accumulated in the intake section and charge air and the connecting piece.
cooler.  
The crankcase ventilation must be checked and replaced, if
n The engine experiences a power loss. necessary.
Fig. 1
 U ncontrolled overspeeds resulting in the engine (so-called “rising”)  The piston and piston rings must be checked for wear and replaced,
Carbonised oil return line
due to the engine oil accumulating in the charge air cooler, which is if necessary.
blown into the intake of the engine and combusted.  A new charge air cooler and air filter should always be installed when
n The guide vanes might be coked in a VTG turbocharger. replacing the turbocharger. In addition, an oil change including oil
filter replacement must be carried out.
Contaminated oil

Contaminated oil
CAUSES
 
If the oil return line of the turbocharger is clogged (Fig. 1) or con-
stricted by a kink, the oil can no longer flow out of the turbocharger
(Fig. 2, diagram B). A possible cause for clogged oil return lines is
the coking of the return line, which might be due to missing heat
shields, a poorly routed return line, heat soak, inadequate oil quality,
or the use of liquid sealants. As the turbocharger is still supplied
with oil from the engine circuit, the oil then escapes to the turbine or
compressor side.
Oil leakage at

Oil leakage at
 If the engine is supplied with too much oil, the oil can no longer flow
turbocharger

turbocharger
back out of the oil return line into the oil pan (Fig. 2,­diagram C). The
crankshaft also splashes up the oil. This results in the oil foaming, Fig. 2
Oil leakage at turbocharger. Diagram A shows the optimum state.
which forms an additional barrier for the returning oil from the turbo-
charger (Fig. 2, diagram D).
 
If the pressure in the crankcase is too high—either because of too
high blow-by (Fig. 2, diagram E) or due to blocked crankcase ven-
Foreign object damage

Foreign object damage

tilation (Fig. 2, diagram F)—, this pressure will also be transferred
to the oil return line of the turbocharger. The oil drainage from the
turbocharger is thus hindered, and the oil escapes from the turbine
or compressor side.
Damage due to excessive

Damage due to excessive

exhaust temperatures

exhaust temperatures
Overspeeding

Overspeeding
10 | © MAHLE © MAHLE | 11
 5 Foreign object damage 6 Damage due to excessive
exhaust temperatures
If foreign substances, such as dust, sand, screws, parts of piston Each turbocharger is designed for only a defined temperature range.
rings or valves, and sediments, enter on the intake or exhaust side, If this range is exceeded, the turbocharger can fail after just a few
Preface

Preface
this will usually lead to total failure of the turbocharger due to the seconds.
very high speeds. Damage to the charge air cooler might also be the
consequence. EFFECTS
n Cracks in the housing of the turbocharger (Fig. 1).
EFFECTS  
Oil lines can become coked: If the supply line is carbonised, the
Inadequate lubrication

Inadequate lubrication
 
On account of previous damage, foreign substances from the turbocharger will not be sufficiently supplied with oil. If the return line
engine or the exhaust manifold can damage the gas entry edges of becomes coked, the oil can no longer flow off and oil is forced out
the turbine wheel. Fig. 1 of the turbocharger (see also section “4 Oil leakage at turbocharger”
 T he air guide plates of the VTG unit are damaged and bent (Fig. 1), Crack in the turbine housing on page 10).
leading to a significant power loss.
Fig. 1
 Foreign substances in the intake air result in damage to the impeller CAUSES
Damaged air guide plates of the VTG unit
(Fig. 2). The vanes might become completely worn as a result. In  The temperature level has changed due to tuning.
addition, the intake passage of the compressor housing might be  Combustion faults have occurred in the engine.
damaged (Fig. 3). n The engine was turned off while still hot.
 The impeller might be damaged by condensation frozen in the intake
Contaminated oil

Contaminated oil
section. Damage to just one vane is characteristic of this cause: REMEDY/PREVENTION
owing to the high speeds, the ice particles burst when encountering  T he turbocharger may only be installed in the specified vehicles.
the first vane, with no other vanes being damaged (Fig. 4).  T he turbocharger may only be installed and operated in the original
state as supplied. Technical modifications are not permitted.
CAUSES  T he engine must always be cooled down at moderate speeds after
 
If a valve is torn off or the piston rings fracture, for example, these high stress, such as driving at full load.
parts come into contact with the guide vanes of the VTG unit and
the turbine wheel via the exhaust manifold. Fig. 2
 Both a leakage in the intake section and a contaminated or defective Impeller damaged by foreign substances
Oil leakage at

Oil leakage at
air filter can be the cause of penetration by foreign substances in the
turbocharger

turbocharger
intake section.
 In winter, ice can form through condensation in the intake section.

REMEDY/PREVENTION
n The leak tightness of the intake section must be guaranteed.
 After working on the intake section, it must always be ensured that
Foreign object damage

Foreign object damage

no loose parts remain there.
 T he air filter must be replaced as specified by the manufacturer, and
the air filter housing as well as charge air line should be cleaned by
suction.
n Only driving short distances should be avoided.
Fig. 3
Foreign substance impact in the intake passage of the
compressor housing
Damage due to excessive

Damage due to excessive

exhaust temperatures

exhaust temperatures
Fig. 4
Only one vane of the impeller damaged
Overspeeding

Overspeeding
12 | © MAHLE © MAHLE | 13
 7 Overspeeding

The parts installed in the turbocharger are designed for a defined

speed range. If this range is exceeded, major turbocharger damage
Preface

can occur within seconds.

EFFECTS
 
Small dents can be seen on the rear of the impeller (Fig. 1). The
material (mostly aluminium) has deformed plastically due to high
Inadequate lubrication

centrifugal forces at overspeeds. It begins to flow and the outer

diameter increases.
 
If the speeds increase further, the impeller can come into contact
with the housing and/or break apart (Fig. 2).

CAUSES Fig. 1
Dents on the rear of the impeller
 The maximum permissible speed of the turbocharger was exceeded
due to tuning.
 
The VTG air guide plates become blocked in the position for
low speeds due to carbonisation. If the engine speeds are then
Contaminated oil

increased, the turbocharger enters the overspeed range.

 The pneumatic or electric control is defective or leaking.

REMEDY/PREVENTION
n The turbocharger must always be left in the original state as supplied.
 T he turbocharger may only be installed in the specified vehicles.
 T he engine must always be cooled down at moderate speeds after
high stress, such as driving at full load.
 O nly engine oils specified by the vehicle or engine manufacturer
Oil leakage at

may be used.
turbocharger

 T he maintenance intervals according to the manufacturer's recom- Fig. 2

Broken-apart impeller
mendations should always be complied with.
Foreign object damage
Damage due to excessive
exhaust temperatures
Overspeeding

14 | © MAHLE © MAHLE | 15