Failure Analysis

In an attempt to help our customers identify the issues with their turbochargers, we have provided a simple visual below with the possible symptoms and diagnosis.

The lubrication system ensures the shaft and bearings are soaked in a constant, clean film of oil to prevent damage from direct contact with each other. As a result, it plays an essential role in prolonging the life expectancy of a turbocharger.

Lubrication failure often results in the excess wear and/or scarring on the bearing surfaces, which increases the clearance between the rotating component and creates excess shaft motion. Over time, this can have an adverse impact on the turbocharger.

Some common causes of lubrication failure include:

  1. Low engine oil pressure/level
  2. Blocked oil supply/drain lines
  3. Inappropriate weight of oil
  1. Contaminated oil
  2. Quick start-up of turbocharger in cold temperature
  3. Hot shutdown of turbocharger (i.e. engine is turned off at high rpm or temperature) resulting in instant oil flow loss and overheating

The causes of the lack of lubrication or lubrication failure can be segmented into external, internal causes and contaminated oil.

  1. External lack of lubrication is caused by anything exterior of the turbocharger affecting the oil flow, such as supply or drain lines and engine blow. The thrust and journal bearings and turbine shaft will show signs of heat discolouration as well as wear from the resulting shaft motion. The wear will appear smooth or “wiped” without any significant scorings.
  2. Internal lack of lubrication is seen from the visible smooth or “wiped” wear without any significant scorings on one or more (but not all) of the bearings. This is an indication that one of the oil feel lines has been blocked by contaminated oil or a manufacturing defect.
  3. Contaminated oil is caused by abrasive materials such as dirt, sand, or metal shavings entering the oil passages. They are easily identified with abnormal groove and scratches on the bearings and connecting components.

Foreign objects, such as screws, nuts, sand, metal power and broken air filters, entering the turbine or compressor wheel can severely damage the rotating turbine or compressor wheels.

As both wheels are precisely balanced to spin at extremely high operating speeds required by their application, damage to either wheel will result in an imbalance in the rotating assembly. Similar to lubrication failure, it will result in severe shaft motions and cause almost every component of the turbocharger to breakdown and fail.

Most often, the damage is easily recognised at the compressor or turbine wheel without removing the housing.  The wheel could also display small pits across the vanes or minor wear on the inducer tips. This is caused by the gradual erosion of the wheel from fine particles such as sand or dirt.

In some rare cases, the compressor wheel lock nut could have loosened off and entered the compressor vanes, which is caused by the lock nut not tightened to the required torque setting.

High exhaust temperature results in the the ‘coking’ of the lubricating oil in the bearing housing drain annulus at the turbine end. This will cause oil leakage into the turbine house and visible coke and carbon deposits at the back of the turbine wheel, which will damage both the turbine wheel and thrust bearing.

The turbine shaft will also display visible heat discolouration and the piston ring in the turbine side of the bearing housing will appear relaxed.

High exhaust temperatures can originate from several operating conditions such as:

  1. Incorrect fuel ratio (high fuel setting)
  2. Insufficient air supply caused by a clogged air cleaner, etc.
  3. Leak in the intake manifold or piping
  4. Excessive exhaust restrictions
  5. Plugged in aftercooler core