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How
does turbocharging work, and what kind of maintenance is necessary?
J.W., via e-mail
In simple
terms a turbocharger is composed of two sealed chambers containing fan
blades or turbines that are connected by a shaft. Exhaust passes through
the first chamber or “hot side” shortly after it leaves the
cylinders, spinning the turbine. The higher the volume of exhaust gases,
the faster the turbine spins. The spinning turbine in the other chamber,
called the “cold side,” draws in outside air and pumps it
into the intake manifold and eventually the cylinders. When the turbine
spins fast enough to exceed atmospheric pressure, the turbocharger is
said to have generated boost, which is usually measured in pounds per
square inch or bar.
Because
turbocharging uses otherwise wasted energy, any horsepower produced is
pure gain. Moreover, boost is directly related to engine load. When there’s
little or no load, little or no boost is produced, output is moderate,
and engine wear is minimal. The more load, the higher the boost and the
greater the power output. A turbocharged engine burns more fuel than a
naturally aspirated one because it produces more horsepower, but on the
basis of fuel used to produce one horsepower—brake-specific fuel
consumption—a turbocharged engine is far more efficient.
While
the turbocharger is a mechanically simple device, it demands careful maintenance
to keep it operating at optimum efficiency. The area between the hot and
cold sides contains a bearing that carries the shaft that connects the
compressor and exhaust turbines. This assembly can spin at upwards of
100,000 rpm, and the only thing separating it from catastrophic failure
is a thin film of oil. Therefore, proper lubrication, including regular
oil and filter changes, is important. In addition, use only oil designed
for turbocharged diesel engines (i.e., SF-DD) on each oil container. And
as both ends of the shaft have seals to prevent oil from leaving the bearing
housing or to prevent exhaust or pressurized air from entering it, these
locations should be inspected on a regular basis.
Other
maintenance concerns include checking air cleaners and intakes for clear
passage and monitoring zincs in the intercooling system if it is raw-water
cooled. You may also want to look at operational recommendations regarding
starting, stopping, and proper rpm range as contained in the engine owner’s
manual.
I
suspect a problem with my alternator. How do I check it out if I do not
have a battery-charger circuit?
A. E., via e-mail
Most
alternator outputs are controlled by a constant-voltage regulator set
between 13.8 and 14.4 volts. With that in mind, start your engine and
let it run for a few minutes. Measure the starting-battery voltage at
the battery terminal with your multimeter set on D.C. volts. If the voltage
reading remains around 12, you probably have a faulty alternator since
it is not outputting a charge back to the battery.
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