Q & A — February 2002
By Capt. Ken Kreisler
a turbocharger works and how to maintain it, checking an alternator, outboard
cooling system maintenance, and more.
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.
This article originally appeared in the January 2003 issue of Power & Motoryacht magazine.