drain passage and drain line allows oil to return to the
engine oil pan after passing through the turbo bearings.
Sealing rings (piston-type rings) are placed around
the turbo shaft at each end of the turbo housing,
preventing oil leakage into the compressor and turbine
Turbochargers require little maintenance between
overhauls if the air cleaners are serviced regularly
according to the manufacturers recommendations. The
turbocharger turbine requires periodic cleaning to
remove carbon deposits that cause an unbalanced
condition at the high relative speeds at which the turbine
Turbocharging system problems usually show up as
inadequate boost pressure (lack of engine power),
leaking shaft seals (oil consumption), damaged turbine
or impeller wheels (vibration and noise), or excess
Refer to a factory service manual for a
detailed troubleshooting chart. It will list the
common troubles for the particular
There are several checks that can be made to
determine turbocharging system conditions. These
checks include the following:
Check connection of all vacuum lines to the
waste gate and oil lines to the turbocharger.
Use regulated, low-pressure air to check for
waste gate diaphragm leakage and operation.
Use a dash gauge or a test gauge to measure boost
pressure. If needed connect the pressure gauge
to the intake manifold fitting. Compare to the
Use a stethoscope to listen for bad turbocharger
Turbo lag refers to a short delay before the
turbocharger develops sufficient boost (pressure above
As the accelerator pedal is pressed down for rapid
acceleration, the engine may lack power for a few
seconds. This is caused by the impeller and turbine
wheels not spinning fast enough. It takes time for the
exhaust gases to bring the turbocharger up to operating
speed. To minimize turbo lag, the turbine and impeller
wheels are made very light so they can accelerate up to
A turbocharger intercooler is an air-to-air heat
exchanger that cools the air entering the engine. It is a
radiator-like device mounted at the pressure outlet of
Outside air flows over and cools the fins and tubes
of the intercooler. As the air flows through the
intercooler, heat is removed. By cooling the air entering
the engine, engine power is increased because the air is
more dense (contains more oxygen by volume).
Cooling also reduces the tendency for engine
A waste gate limits the maximum amount of boost
pressure developed by the turbocharger. It is a butterfly
or poppet-type valve that allows exhaust to bypass the
Without a waste gate, the turbocharger could
produce too much pressure in the combustion
chambers. This could lead to detonation (spontaneous
combustion) and engine damage.
A diaphragm assembly operates the waste gate.
Intake manifold pressure acts on the diaphragm to
control waste gate valve action. The valve controls the
opening and closing of a passage around the turbine
Under partial load, the system routes all of the
exhaust gases through the turbine housing. The waste
gate is closed by the diaphragm spring. This assures
that there is adequate boost to increase power.
Under a full load, boost may become high enough to
overcome spring pressure. Manifold pressure
compresses the spring and opens the waste gate. This
permits some of the exhaust gases to flow through the
waste gate passage and into the exhaust system. Less
exhaust is left to spin the turbine. Boost pressure is
limited to a preset value.
What device is used between the supercharger
outlet and the engine to cool the air?
Q28. In a turbocharger, what prevents oil from leaking
into the compressor and turbine housing?