This question is asked most often when the turbo
is stuffed. It is mostly oil related but sometimes
it's demaged from old age,fatigue from the blade
of the rotor falling off or could be thrust failure
from low oil pressure, wrong blowoff valve
adjustment or size or air intake restrictions.
Some turbo's are demaged beyond identifying
any evidence of why it failed.

Turbochargers are very reliable and can outlast the
life of the engine.Only poorly set up or unserviced
oil can hurt a turbo.

Here is a list of faults and causes.

SMOKEY

If you suspect it's the turbo causing the smoke,
could the engine be at fault? Check the engine
condition,oil drain blockage,or air cleaner
blocked.If these are 'ok', pull off the air intake
of theturbo and feel for radial or axial play.
All journal bearing turbo's have some radial play
(About '12 thou or.25 mm).
If this is'ok',check oil condition,maybe there is
carbon build up somewhere.If all external causes
are 'ok' get the turbo serviced.

---

NOISY

Usually only noisy from demage or missing
blades,sometimes it could be something hitting
the blades or maybe worn journal bearings
(check oil pressure/condition).
An out of balance rotor could be the cause but
usually it would need to be badly out of balance
to start warping at speed.

---

LOW BOOST

This could be many things but with the turbo it
could be demaged compressor wheel or turbine
wheel blades,tight spinning rotor or cracked,
broken or seized wastgate.If any of these are
faults the turbo needs to be removed.
Other things which cause it is pipeing leaks,
blokages,exhaust blockages,ignition fault or
blocked air intake.Also worn bearings can
slow the rotor causing
low boost.

---

THRUST FAILURE

Caused possibly from low oil pressure or blowoff
valve setting. Undersize compressor wheel can
cause it to if flow of engine or boost is increased.
Get turbo serviced and include heavy duty thrust
bearing if the engine flow is increased.
Also a restricted air intake can cause it.

---

BROKEN COMPRESSOR WHEEL BLADES

Similar to turbine wheel breakage causes
,but without the heat.Mostly caused by blow off valve setting or
type.It mainly brakes one blade off and that
takes out the others behind it while it's trying to
get sucked through the compressor wheel.A foreign
object can obviously brack off a blade when it hits a
100000rpm compressor wheel. It also can caused
by blow off valve setting or type but this is rare.

RADIAL PLAY

If this is more than normal (about .5 mm) then it is
either low oil pressure or out of balance both would
wear journal bearings.Check reasons for low oil
pressure or blockage oil feed to turbo also check for
out of balance signs (broken blades,demage,ect).
This problem needs urgent repair!
Look here-projects

EXHAUST GAS LEAK
FROM TURBO

Easily fixed but only with the turbo removed ,by
machining the mounting flange face if it needs it and
installing a new gasket if that is where the leak is.
On bad cases of this it can cause low boost.

BROKEN COMPRESSOR
WHEEL SHAFT
OR SPUN
COMPRESSOR WHEEL

Mostly from back fire or blow off valve.Spinning
compressor wheel off can only happen on shafts
with right hand threads holding the compresser
wheel on but can move wheel andshift out of
balance on left hand nut shafts