Turbocharger Failure Diagnosis Guidelines

In my practice I several times observed that very often fully functioning turbochargers are replaced, because the problem shows up at the turbo, although the turbocharger is in good condition.

As a general rule, if both the Radial- and Axial clearances are within tolerances and there is no visual damage to both compressor- or turbine wheel, it is most of the time very unlikely, that the turbocharger is faulty. We should identify the cause of the problem first! Is it a turbo problem and must the turbo be replaced? Or is it an engine problem, showing up at the turbocharger? If your engine is not operating properly, you should not automatically assume, that the turbocharger is causing the problem. In many cases a turbocharger is replaced, although the fault is engine related and not caused by malfunctioning of the turbo.

Therefore, always carefully carry out Turbocharger Diagnostic to identify the problem, before removing the turbo from the engine.

Turbocharger service and lifetime

The turbocharger is designed to typically last as long as the engine. It requires no special maintenance, with inspection limited to a few routine checks. To ensure the turbocharger's lifespan aligns with the engine's, it is essential to strictly adhere to the engine manufacturer's service guidelines and follow them accordingly.

• Oil change intervals
• Oil filter system maintenance and replacement
• Oil pressure control
• Air filter system maintenance and replacement

What are the main factors causing turbocharger failure?

90 % of all turbocharger failures are due to the following causes:

• Penetration of foreign parts into the turbine or the compressor of the turbocharger

• Dirt/contamination in the lubrication oil of the engine, also lubricating the turbo bearings

• Insufficient/inadequate oil supply (oil pressure/filter system/engine start up-shut down)

• High exhaust gas temperatures (incorrect fuel injection system)

Never continue to operate an engine with a suspect or noisy turbocharger as this could result in total engine failure.

Insufficient oil supply can be attributed to the following:

• Re-fitting a turbocharger without adequate priming
• Long periods of non-use
• Broken or restricted oil feed pipe
• Low engine oil pressure due to malfunctioning lubrication system
• Low or no oil in sump
• The use of sealants, which can restrict the oil flow
• Not priming a replacement oil filter with new oil. If this cannot be done, then crank the engine with no fuel to establish oil pressure
• Do not exceed idle conditions until oil pressure is established.

Contaminated oil harms the turbocharger by causing severe scoring on critical bearing surfaces. To prevent damage, use oil and filters of the quality recommended by the engine manufacturer. These should be replaced when installing a new turbocharger and regularly, following the vehicle or engine manufacturer's guidelines.

Dirty oil damage could result from:

• Blocked, damaged or poor-quality oil filter
• Dirt introduced during servicing
• Engine wear or manufacturing debris
• Malfunctioning oil filter by-pass valve
• Degraded lubrication oil

Failure caused by excessive exhaust temperatures or hot engine shutdown leads to carbon buildup. It is advised to let the engine idle for two to three minutes to allow the bearing system to cool before shutting it down.

Heat soak from the turbine end into the bearing housing causes oil carbonization and bearing system corrosion. The primary damage occurs to the shaft seal ring and grooves, turbine-end bearing, and the blockage of the oil drain cavity in the bearing housing.

Carbon build-up can be caused by:

• Hot shutdown of engine
• Degraded oil quality carbonizing in service
• Infrequent oil change intervals causing oil breakdown in service
• Air and gas leaks
• Faulty fuel injector pump/injectors.

Before changing your turbocharger, please make sure that you have correctly identified the cause of the fault.

Excess smoke

Caused by:

? Dirty air cleaner

? Air intake system restriction

? Cracked mounting flange/gasket

? Fuel pump/injectors/valve timing

? Wastegate mechanism set

? Turbocharger damaged.

Engine lacks power

Caused by:

? Dirty air cleaner

? Air intake system restriction

? Cracked mounting flange/gasket

? Exhaust for foreign object

? Fuel pump/injectors/valve timing

? Burnt valves and/or pistons

? Turbocharger damaged.

Noisy/Whistling

Noise often arises from air or gas escaping due to pre-turbine exhaust leaks or air/boost leaks. Inspect all joints thoroughly. If the noise persists, examine the turbocharger's clearances and check the wheels for contact with the housing.

Seized/Sluggish

If the turbocharger rotor assembly is seized or difficult to rotate, it is often caused by lubricant degradation, leading to excessive carbon buildup inside the bearing housing, which hinders rotation. Inadequate or fluctuating oil pressure can also result in rotor seizure, as well as the introduction of contaminants into the oil system.

Worn/Excessive clearance

A turbocharger has defined axial and radial rotor clearances. If these clearances deviate from the specified range, the issue could be linked to a lubrication problem, such as inadequate oil supply, contamination with debris, or oil mixed with coolant.

Remember, if the root cause of the problem is not identified and corrected, your problem will remain!