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Troubleshooting Turbos with Carwood: Oil Contamination

Since 95 percent of turbo failures are caused by issues, other than the turbo itself, it’s important to determine why it failed, and fix it, before a new one is fitted. If not, the replacement unit could fail too, costing you, and your customer, more time and money. Leading turbo manufacturer, Carwood, explains all you need to know about oil contamination, a common cause of turbo failure.

What is oil contamination?

With tolerances measured in microns, and operating speeds of over 300,000 revs per minute, today’s modern turbochargers require a constant supply of clean, good quality oil to keep them running properly. Unfortunately, dirt, fuel, water, combustion residues and other contaminants can easily contaminate the oil, with even the smallest particles causing rapid wear to key components, and potentially serious damage to the turbocharger, and sometimes the engine.

Oil contamination – scoring on shaft

What causes oil contamination?

Contaminated oil can be caused by a number of issues, the most likely being:

  • a damaged, blocked or poor-quality oil filter and/or filter bypass valve
  • a build up of carbon in the engine and/or oil supply lines
  • degraded engine oil due to excessive temperatures and/or extended service intervals
  • internal engine leaks causing water, fuel or coolant to mix with and dilute the oil
  • accidental introduction of dirt or debris into the system during servicing
  • metallic shavings or swarf deposits from engine wear, propagating debris throughout the entire system
  • other foreign matter such as dust and dirt entering the engine cylinders through the air intake system.

What are the signs of oil contamination?

Like oil starvation, contaminated oil will manifest itself in performance issues and component wear. Symptoms to look out for include:

  • check engine light illuminated – further diagnostics will be required to pinpoint the issue
  • loss in vehicle power – limp home mode
  • grooves/scoring to journal bearing, journal bearing diameters of shaft, wheel and thrust components
  • internal damage to the shaft and bearing from larger particles
  • wear to oil flinger/flinger grooves leading to potential oil leaks
  • excessive wear or damage to piston rings causing oil to enter the turbine side and increased oil usage
  • the turbine and/or compressor wheel coming into contact with the housing bore, due to excessive play in the shaft from worn bushings/bearings
  • blocked internal oil galleries restricting oil flow
  • smell of fuel in the oil
  • particles in the oil.

Oil contamination – scoring to bearings close up

How to prevent oil contamination

The risk of oil contamination can be mitigated by following best-practice service procedures, such as:

  • fit new, OE-quality oil filters at recommended service intervals and when refitting a replacement turbo
  • flush and change the engine oil with the correct grade and quantity of oil, as per VM guidelines
  • fit new in-line micro filters and oil feed and return pipes, whenever installing a replacement turbo
  • check the entire oil supply system during every service, and clean or replace components as needed
  • only ever use OE-quality fitting accessories – inferior quality gaskets and seals can easily break up and cause irreparable internal damage
  • take care when servicing the vehicle to avoid any accidental contamination: cap components and/or pipes, keep the working area clean of dust, chemicals etc, use clean tools, and check you have them all when the job is complete
  • never use liquid sealant – it is liable to harden and break up when exposed to heat
  • check the engine for signs of wear, including swarf deposits.

Oil contamination – wear to thrust pad AKA thrust bearing

How to resolve oil contamination

If an oil contamination related failure is confirmed, it’s important to address and fix the root cause, before replacing the turbocharger. Remedial actions should include:

  • conduct an oil system flush following VM guidelines to ensure any trace of contaminated oil is removed
  • fill with the correct grade and quantity of oil
  • fit new OE-quality oil filters, gaskets and oil supply lines
  • thoroughly clean the entire oil supply and return system – this may require the removal of the sump, oil pump and internal oil lines – replace parts as needed
  • when replacing the turbo, perform an oil pressure test to identify issues in the oil supply and return system.

Whilst this may add additional expense to your customer’s bill, it is far more cost and time-effective than having to fit another turbo, and potentially an engine, when they return with the same issue soon after.

For further support and advice, call Carwood’s turbo technical hotline on 01623 867966. Or for more on its range of OE-quality, competitively priced remanufactured turbochargers and accessories, visit

About Autotechnician
Autotechnician is a magazine published nine times a year, delivering essential information to independent garage owners and technicians in the UK. Delivered both digitally and in print, autotechnician provides readers with technical, training, business advice, product and news, allowing our readers to keep up to date with information they need to run and work within a modern workshop.
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