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I DRIVE a 2001 model Jetta 4 TDI with 160 000km on the clock. I want to know when the turbo will fail and when is it time to replace it. Is it possible to clean the entire turbo system?
That's a very good question, Jabulani. What are the early warning signs of a turbo going bad, signs that the average owner can pick up without special equipment?
If one knows what to look out for, the turbo can be rebuilt in time to avoid a catastrophic failure that could do widespread damage to the engine. Here's a brief list of symptoms that might indicate problems in the turbocharger:
l Noises that weren't there before.
Because the vaned wheels inside a turbocharger and the shaft joining them rotate at enormously high speeds the wheel assembly is balanced to very fine tolerances.
Any imbalance or unwanted play that develops in the wheel assembly over time, might give rise to a whining sound. The wobble will not only affect the turbo's performance, but will accelerate wear in the shaft bearings.
Thus the wobble will increase until the vanes of the wheels begin to touch the inside wall of the housing.
At that point a metallic screech will be emitted and the friction will prevent proper spool-up and hinder full-boost performance.
The scraping will wear down the vanes, leading to more imbalance, and so on, in a vicious circle:
lAbnormal smoking at the exhaust, especially white or blue-white smoke.
This can come from the oil fed to the shaft bearings in the turbo getting past the sealing rings at the ends of the shaft and entering the hot exhaust gas on the turbine side or the inlet air on the compressor side.
lOn a turbo-charged petrol engine puffy white smoke at idling is an ominous sign. On a turbo-diesel, oil vapour in the inlet air is a dangerous thing because it can cause the engine to "run away" uncontrollably and self-destruct due to over-revving.
lThe same thing can happen, incidentally, if a blocked air cleaner coincides with abnormal amounts of oil vapour in the crankcase, perhaps due to the sump being overfilled, or excessive blow-by.
lThe compressor will then try to make up for the restriction in the air cleaner by sucking extra hard on the crankcase ventilation system, inhaling a lot of oil vapour in the process.
lA drop-off in engine performance, due to a sick turbocharger no longer providing the same boost, will sometimes be the first warning sign picked up by a driver who knows the vehicle well.
If any of these symptoms are noticed, you can remove the rubber duct feeding air from the air cleaner into the compressor side of the turbo. The compressor wheel will then be visible and you can inspect it by a good light for evidence of scraping or damage to the vanes caused by foreign objects striking them.
lDue to the design of the shaft bearings, it's normal to feel some radial play on the wheel when it is stationary, but it should have hardly any axial play.
lYou can also remove the hose fitted to the outlet opening of the compressor housing, taking air to the inlet manifold via the intercooler, and examine it closely for oil deposits. Anything more than a slight film of oil vapour condensate in this hose calls for immediate further investigation by a turbo specialist. He will probably recommend that the entire inlet tract downstream of the turbo be cleaned out if there is serious oil intrusion. If you catch a compromised turbocharger before it disintegrates, it does not have to cost the earth to have it rebuilt.
Replacement cartridges, consisting of new compressor and turbine wheels together with a new shaft and shaft bearings, all pre-assembled and balanced, are available for many turbochargers. But it is a job for a turbo specialist, not for the home mechanic.
To extend the life of a turbocharger experts advise that you allow for a cooling period after stopping and starting up .