TDI turbocharger faulty: The 9 most common causes of turbocharger damage and repair
TDI turbocharger failure: the 9 most common causes
Turbocharger damage can have many different causes. Accurate failure analysis of the defective turbocharger is crucial to prevent damage recurring soon after repair or replacement.
In this article, we show the nine most common damage patterns in TDI turbochargers, explain possible technical causes and outline which components should be checked before a new turbocharger is installed.
The 9 most common causes of turbocharger failure
Click on a damage pattern to jump directly to the technical description, possible causes and recommended checks.
Thrust bearing and thrust washer
Damage caused by excessive exhaust back pressure and axial loading of the turbine shaft.
Cause 2Main bearing damage caused by oil dilution
Fuel in the engine oil reduces viscosity and lubricating ability.
Cause 3Main bearing damage caused by insufficient lubrication
Insufficient oil pressure or an interrupted oil supply damages the bearing surfaces.
Cause 4Oil contamination and foreign particles
Particles in the engine oil attack the turbocharger's heavily loaded plain bearings.
Cause 5Turbine geometry on the exhaust side
Foreign objects from the exhaust manifold, engine or EGR system damage the turbine wheel.
Cause 6Compressor wheel on the intake side
Foreign objects in the intake tract strike the compressor wheel as it rotates at high speed.
Cause 7Overspeed damage
Faulty control, leaks or tuning can cause the permissible speed to be exceeded.
Cause 8Oil leakage at the turbocharger
Problems with oil return, crankcase ventilation or pressure conditions lead to oil leakage.
Cause 9Excessive exhaust gas temperature
Thermal overload damages the housing, lubrication and material structure.
Have turbocharger damage professionally analysed
Using the 07eins Turbo-Check we carry out professional analysis and inspection of defective turbochargers. The damage pattern helps determine the right approach to repair and replacement.
For Volkswagen VW T5 2.5 TDI engines, we also have double-checked, factory-new 07eins turbochargers for VW T5 2.5 TDI engines available.
Damaged turbine shaft thrust bearing and thrust washer
Excessive exhaust back pressure can push the turbine shaft axially against the thrust washer and permanently damage the turbocharger's bearing surfaces.
Description of the damage
The turbine shaft's thrust bearing consists of a thrust washer made from a special copper alloy. If pressure in the exhaust flow rises excessively during operation, this loads and displaces the turbine shaft against the axial thrust washer.
Beyond a certain point, the oil pressure in the system is no longer sufficient to keep the bearing surfaces apart. This causes surface damage to the bearing material.
The damaged surfaces cause a further local drop in oil pressure, accelerating the damage. Increasing friction initially reduces turbocharger speed and power, eventually leading to complete turbocharger failure.
Excessive exhaust back pressure
In many cases, excessive exhaust back pressure is caused by a blocked diesel particulate filter. Soot and deposits can block the fine channels in the filter medium, significantly reducing the cross-section available for exhaust gas flow.
This restriction raises the pressure in the exhaust tract and thus increases the axial load on the turbine shaft.
Why a diesel particulate filter can become blocked
- Short journeys: Low operating temperatures produce more soot. The filter cannot regenerate completely.
- Absent or ineffective regeneration: If the necessary exhaust gas temperature is not reached, soot deposits remain in the filter.
- Fuel quality: Water, particles or poor-quality fuel can promote deposit formation.
- Exhaust gas recirculation malfunction: Faulty EGR can increase soot production.
- Defective injectors: Incomplete combustion produces additional soot.
- Vehicle age and mileage: As mileage increases, so does the risk of deposits and wear.
- Driving style: Frequent hard acceleration and braking can increase soot production.
- Insufficient air: Too little fresh air leads to incomplete combustion.
Repair recommendation
The measures depend on the degree of blockage and the specific vehicle.
- Forced regeneration: For a lightly loaded filter, an appropriate driving cycle or workshop-assisted regeneration may help.
- Chemical cleaning: Special cleaning products can loosen deposits, provided they are used according to the manufacturer's instructions.
- Professional cleaning: Specialist companies clean DPF systems using appropriate methods.
- Replacement: A severely damaged filter or one that can no longer be regenerated must be replaced.
- System check: EGR, the injection system and other emissions-related components must be checked for the underlying cause.
Main bearing damage caused by oil dilution
If diesel fuel enters the engine oil, viscosity and lubricating ability decrease. This can damage the turbocharger's heavily loaded bearings in particular.
Description of the damage
The turbine shaft bearing assembly consists of thrust bearing washers and a radial material pairing for the central plain bearing. A constant film of fresh oil prevents the bearing materials from coming into direct contact with the turbine shaft surface.
If this oil film is interrupted or the engine oil loses its lubricating properties through chemical changes, the bearing surfaces come into contact. This causes surface damage.
The damaged surfaces lead to further pressure loss and increasing friction. Turbocharger speed drops until power is lost or complete failure occurs.
Insufficient lubricating ability
The damage pattern indicates that the engine oil has insufficient lubricating ability. This is particularly often caused by fuel entering and diluting the engine oil.
How oil dilution occurs
Oil dilution occurs when fuel enters the engine oil and reduces its viscosity. In unit injector engines, leaking injector seats or unit injector seals are a possible source.
Diesel fuel, which lacks adequate lubricating ability, reduces the engine oil's lubrication performance. Over time, this can damage the turbocharger's heavily loaded plain bearings.
Excessively extended oil change intervals can also significantly reduce the engine oil's lubricating ability.
Possible causes of oil dilution
- Short journeys: Unburnt fuel can enter the oil if the engine remains cold.
- Faulty injectors: Incomplete combustion promotes fuel entering the oil.
- Defective fuel pressure regulator: Excessive pressure can lead to over-fuelling.
- Incorrect injection timing: Faulty injection can impair combustion quality.
- Engine problems: Worn piston rings or other mechanical damage can promote fuel entering the oil.
- Crankcase ventilation: A defective system can promote fuel vapours and condensate in the oil.
- EGR malfunction: Incomplete combustion can increase fuel contamination.
- Excessive fuel pressure: Excessive system pressure can cause too much fuel to be injected.
Repair recommendation
The cause of the inadequate lubricating properties must be fully investigated and eliminated.
If diesel is suspected of entering through the unit injector seats or seals, we recommend inspection and professional repair of the PD injector area.
Depending on the engine, the 07eins PD injector bridge or the 07eins PD injector retainers may be suitable.
After the repair, a complete oil and filter change in accordance with the manufacturer's specifications is necessary.
Main bearing damage caused by insufficient lubrication
If oil pressure or oil quantity does not reliably reach the turbocharger bearings, the load-bearing lubricating film breaks down and the bearing surfaces come into direct contact.
Description of the damage
The turbine shaft bearings are lubricated by a constant flow of engine oil. If this oil film is interrupted, the bearing surfaces come into direct contact.
This produces scoring and surface damage. Friction increases, oil pressure falls further locally, and the damage develops at an accelerating rate.
Insufficient oil supply
The damage pattern indicates an insufficient oil supply to the turbocharger bearing. Oil pressure, oil quantity and engine oil viscosity are decisive.
Common causes of insufficient lubrication
- Faulty oil pressure control valve: An incorrectly regulating valve cannot maintain the necessary oil pressure over the long term.
- Worn oil pump: Wear can lead to fluctuations in oil pressure and delivery rate.
- Blocked oil passages: Deposits and coke can restrict lines and passages.
- Blocked oil filters: A clogged filter can reduce oil flow.
Why oil filters can become blocked
- Deposits and contamination: Sludge, metal shavings and particles accumulate in the filter medium.
- Oil coking: High temperatures can cause the engine oil to coke.
- Filter ageing: The filter medium loses performance with increasing service time.
- Incorrect oil grade: Unsuitable engine oil can promote deposits and sludge formation.
- Mechanical engine problems: Wear debris increases the quantity of particles in the oil circuit.
- Incorrect filter size: An unsuitable filter may have insufficient capacity or flow performance.
Repair recommendation
The cause of insufficient oil pressure must be fully investigated. All direct oil feed and return lines for the turbocharger should be checked particularly carefully after this type of damage and replaced if necessary.
After the cause has been eliminated, a complete oil and filter change must be carried out in accordance with the manufacturer's specifications.
Main bearing damage caused by oil contamination or foreign particles
Suspended particles, metal wear debris or dislodged coke deposits can enter the precision turbocharger bearings through the oil flow and damage the sliding surfaces.
Description of the damage
If the oil flow contains particles or foreign material, these can damage the turbocharger's precision bearing surfaces. The surfaces are attacked and lose their sliding and bearing properties.
The damage leads to increasing friction, decreasing turbocharger speed and ultimately bearing failure.
Foreign particles in the engine oil
The wear pattern indicates foreign material or suspended particles in the engine oil. These can enter the oil circuit through damaged filters, coke deposits or mechanical wear debris.
Where the foreign particles may come from
- Coke deposits: Deposits in lines can loosen and travel into the bearings with the oil flow.
- Damaged or worn oil filter: Damaged filter media can no longer retain particles reliably.
- Mechanical wear debris: Worn engine components can introduce metal particles into the oil circuit.
- Contaminated engine oil: Improper maintenance or dirty filling systems can introduce foreign material.
Repair recommendation
The oil circuit, filters, oil sump and turbocharger feed and return lines must be carefully inspected and cleaned.
After the cause has been eliminated, a complete oil and filter change is required. With severe contamination, more extensive cleaning of the oil circuit may also be necessary.
Damaged turbine geometry on the exhaust side
Hard foreign objects in the exhaust flow can strike the rapidly rotating turbine wheel or VTG mechanism and cause considerable material damage.
Description of the damage
The turbine wheel blades on the exhaust side show damage. Due to the high rotational speeds, even small foreign objects can cause considerable material damage.
The damage pattern indicates that hard foreign objects entered the exhaust flow and struck the turbine wheel or VTG mechanism.
Where the foreign particles may come from
- Fragments of the exhaust manifold: Corrosion and cracking can cause parts of the manifold's inner wall to break away.
- Fragments of exhaust valves: Damaged valve parts can enter the exhaust flow.
- EGR components or deposits: Parts of the valve mechanism or solid deposits can break away.
Repair recommendation
The source of the foreign objects must be fully identified. In particular, the inside of the exhaust manifold should be carefully inspected whenever this type of turbocharger damage occurs.
A new turbocharger may only be installed after the cause has been eliminated.
Damaged turbine geometry on the intake side
Even the smallest foreign objects in the intake tract can deform, fracture or completely destroy the aluminium compressor wheel at high turbocharger speeds.
Description of the damage
The compressor wheel blades on the intake side are damaged. The compressor wheel is usually made of aluminium and rotates at very high speed during operation.
If even small foreign objects strike the rotating compressor wheel, deformation, chipping and fractures can occur. The resulting imbalance can completely destroy the turbocharger.
How foreign objects enter the intake tract
- Foreign objects in the intake air: Dust, leaves, insects or other particles can be drawn in.
- Leaking connections: Leaks allow unfiltered air to enter the system.
- Poor-quality or damaged air filter: The filter no longer retains particles reliably.
- Damaged air filter housing: Foreign objects can enter the intake tract directly.
- Damaged intake pipes: Broken parts or openings can introduce foreign objects.
- Parts of the air ducting: Clips, sensor parts or plastic fragments can break away.
- Crankcase ventilation: Damaged components or lines can release foreign objects into the intake.
Repair recommendation
The entire air path from the air filter, through the intercooler and pipework to the turbocharger, must be carefully inspected and cleaned.
Even the smallest particles of paper, adhesive tape, plastic or foam can cause massive damage at these high rotational speeds.
Overspeed damage to the turbine shaft and housing
If the permissible turbocharger speed is exceeded, extreme centrifugal forces can damage the compressor wheel, turbine wheel, shaft and housing.
Description of the damage
The turbine wheel, compressor wheel and housing show damage indicating that the permissible turbocharger speed has been exceeded.
Typical signs include scoring on the inside of the housing and deformed or broken blades.
Why the turbocharger overspeeds
- VTG adjustment: Corrosion or wear can prevent the control system from correctly limiting turbocharger speed.
- Leaking charge air circuit: When pressure is lost, the control system tries to compensate for the missing boost pressure by increasing speed.
- Engine management and chip tuning: Increased boost pressure or modified maps can operate the turbocharger outside its safe operating limits.
Repair recommendation
VTG control, the charge air system, pressure sensors, vacuum system and engine software must be carefully checked.
Modified engine software should be considered particularly when the turbocharger has repeatedly suffered overspeed damage.
Oil leakage at the TDI turbocharger
If lubricating oil cannot flow freely from the turbocharger back to the oil sump, it can leak from the turbocharger on the intake or exhaust side.
Description of the damage
A turbocharger in proper technical condition should not show noticeable traces of oil on the intake or exhaust side.
For reliable bearing lubrication, oil feed and oil return must work in a balanced relationship. If the oil cannot flow freely back to the sump, excessive oil pressure builds up in the turbocharger housing.
Why oil leaks from the turbocharger
- Crankcase ventilation: A defect can cause excess pressure in the crankcase and obstruct oil return.
- Blocked oil return line: The engine oil cannot drain back into the sump quickly enough.
- Unfavourable pressure conditions: Incorrect pressure conditions on the intake or exhaust side can promote oil leakage.
- Excessive oil level: A persistently excessive engine oil level can obstruct the return flow.
- Oil dilution: Fuel entering the oil can raise the oil level and reduce lubricating ability.
Repair recommendation
The cause of the oil leakage must be fully identified. Oil return, crankcase ventilation, engine oil level and the charge air system in particular must be carefully checked.
A new turbocharger may only be installed once free oil drainage into the sump has been ensured.
Damage caused by excessive exhaust gas temperature
A persistently excessive exhaust gas temperature subjects the turbocharger housing, bearings, lubricating oil and material structure to loads far beyond the intended operating conditions.
Thermal overload of the turbocharger
A persistently excessive exhaust gas temperature places stress on the turbocharger housing, bearings, lubricating oil and material structure.
If thermal loads exceed the specified limits, cracks, material fatigue, oil coking and complete turbocharger failure can occur.
Why the exhaust gas temperature becomes too high
- Engine software manipulation: Higher injection quantities and boost pressures often also increase the exhaust gas temperature.
- Lubrication damage: Overheated oil loses lubricating ability and can coke.
- Material fatigue: Persistently high temperatures can cause cracks and structural damage.
- Overheating due to exhaust back pressure: Defective or clogged components in the exhaust system increase thermal stress.
- Reduced service life: Repeated thermal overload significantly shortens turbocharger service life.
Repair recommendation
The engine software, injection system, boost pressure control, exhaust system and diesel particulate filter must be checked.
After the cause has been eliminated, a complete oil and filter change and a careful inspection of all thermally stressed components are required.
The cause determines how long the new turbocharger lasts
Turbocharger damage can often be associated with typical damage patterns. However, the key is not just to replace the defective turbocharger, but to identify the original technical cause fully.
The oil supply, oil return, air path, exhaust tract, DPF, engine management and injection system must be carefully checked according to the damage pattern.
The 07eins Turbo-Check helps with professional analysis of the defective turbocharger and assessment of the damage pattern.
Identify the cause first, then repair it properly
A thorough damage analysis can prevent a new turbocharger from being damaged again by an undetected fault.
