Turbocharger failure modes
MOST TURBOCHARGERS fail due to oil starvation ruining the bearings, or ingress of foreign objects causing erosion or break up of the turbine or compressor rotors.
OIL STARVATION: This can be caused by a partially blocked or poor quality oil filter and failure of the filter bypass valve. Excessive carbon in the engine, usually due to incorrect oil and/or poor lubrication servicing can be carried through to the turbo and partially block the oil galleries feeding the bearings, as can metallic particles in the oil from engine wear. Overheated engine oil, caused by driver abusive or cooling system failure, can lose some lubrication qualities – easily avoided by using the engine sympathetically and renewing the oil after an overheat situation.
IMPACT DAMAGE: The compressor rotor can be damaged by erosion or impact from ingestion of foreign particles. Typical causes include a poor quality air filter, inward air leaks between the filter and turbo, or debris from internally damaged hoses, or objects entering the induction system during maintenance work on the engine. This also applies to the exhaust turbine when working on the exhaust manifold. Naturally, fragments from a failure in the engine cylinders will be carried through to damage the exhaust turbine – another reason why cam belts should be changed at the prescribed intervals. Even relatively minor impact damage or erosion can put the unit out of balance, accelerating bearing and seal wear.
CAUSES OF OIL LEAKS: • Worn bearings in the turbo allow axial shaft movement which distorts the oil seals, allowing oil to pass into the turbine and compressor housings. It can also damage the rotating parts of the turbo. • Blocked air filter increases the induction vacuum at idle speeds, drawing oil past worn shaft seals. This leaves the bearing less lubricated and, oil will leak into the induction system and intercooler. A partially blocked or kinked air inlet hose has the same effect. • Similarly, oil can be drawn through worn exhaust turbine oil seals if there are leaks in the exhaust system (such as Td5 manifold warp) or a malfunction of the EGR system. • Oil leaks from the bearings will occur if there is partial blockage in the turbo oil drain pipe.
CAUSES OF REDUCED OIL SUPPLY: • Switching the engine off immediately after a high load/high speed drive so that oil carbonises in the hot bearings (800 deg C is not unusual). • Silicone sealant used on gaskets can ooze out to cause oil flow blockage. • Low engine oil pressure. • Partial blockage of oil drain.
EFFECTS OF THE EGR (EXHAUST GAS RECIRCULATION) SYSTEM: A malfunctioning EGR valve can contribute to a build-up of carbon deposits in the turbine which, in the case of a variable vane turbo, can cause the vane mechanism to stick, with resulting loss of performance.
OUT OF USE: Standing for long periods is not good for wastegate or especially variable vane mechanisms. Regular driving helps keep the vane mechanism working freely.