Troubleshooting turbos: Foreign Object Impact

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 the underlying cause before a new turbo is fitted. If not, the replacement unit could fail too, costing you, and your customer, more time and money. Here, remanufacturer Carwood investigates one of the common issues – damage from foreign object impact.

What is foreign object damage?

Today’s modern turbos spin at speeds over 300,000 rpm and endure temperatures close to 1,000°C. In these conditions, even the smallest of particles sucked into the turbine, compressor or bearing housing can result in immediate turbo failure. Worse still, these same fragments can be carried into the combustion chamber, causing irreversible damage to the engine too.

What causes foreign object damage?

Foreign object damage can be caused by:

• Objects entering the turbo air intake due to a faulty, low-quality or poorly maintained air filter; Worn or faulty turbocharger pipes, hoses and/or connections, allowing debris to bypass the filter into the turbo

• Fragments of gasket material breaking off and entering the unit; Left over debris from a previous turbocharger failure

• Nuts, bolts, washers etc that become loose or are left in the intake pipe due to poor service practices; Debris from damaged engine components can enter the exhaust gas intake and impact the turbine wheel, shaft or VVT

• Exhaust gases containing oil particles, sludge and other coked debris can damage turbine wheel blades; Condensation in the intake section causing ice to form in low temperatures which can damage compressor wheel blades

What are the signs of foreign object damage?

Failure due to foreign object damage is one of the easiest turbo issues to diagnose at the compressor, air intake side of the turbo, given the obvious signs of damage, such as: Chipping, pitting and broken blade – visible on the compressor wheel blade tops; Pitting on or around the compressor air inlet; Excessive movement between the wheel profiles and housing bores – there should be a uniform gap; Damage to nozzle ring blades.

At the turbine side, the turbo may need to be dismantled to gain access to the turbine wheel, shaft and VNT. Signs of foreign object damage here include: Damage to one or more of the VNT vanes; Harsh metallic noises coming from the engine bay as the turbo spools up; Chipping/damage to the blades on the turbine wheel; A bent shaft. Like most turbo failures, other symptoms include loss of power & the check engine light illuminated.

How to prevent foreign object damage…

By following some simple, best-practice advice, the risk of foreign object damage can be minimised:

• Check that the entire air induction system is clean and object free

• Inspect pipework and clamps for signs of wear and tear – replace as necessary

• Always fit OE-quality filters, as specified by the VM
  
• Only ever use new, OE-quality gaskets, seals and fitting kits

• Ensure there is no residual debris from the previous turbo failure

• Never use liquid sealant – it is liable to harden and break- up when exposed to heat

How to resolve foreign object damage…

If damage is identified, it’s important to remove and clean components, hoses, etc. If it’s a two-stage turbo, ensure you do both the high and low-pressure sides. Thoroughly clean the entire air supply system including the pipework, intercooler and EGR to ensure it is completely free of any particles – any concerns, replace the whole system. Flush and change the engine oil, fit a new OE-quality oil filter, as per the VM spec and inspect the oil supply, return pipes, in-line filters and fittings for evidence of foreign objects and replace as needed – this may require removal and cleaning of the sump and oil pump.

Whilst following the above may add to your customer’s bill, it is far more cost and time-effective than having to fit another turbo, or an engine, soon after.

For further support and advice, call Carwood’s turbo technical hotline on 01623 867966, or visit

www.carwoodecat.co.uk

How to guide – How to fit a turbo charger.