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My new boat has a single turbocharged diesel. Can you give me a primer on how it works and the maintenance involved? C.R., via e-mail
A turbocharger is a mechanically simple device composed of two sealed chambers containing fan blades--also known as turbines--connected by a shaft. Exhaust passes through the first chamber, which is made of cast iron and is also called the "hot side," spinning the turbine. This causes the turbine on the "cold side," which is made of aluminum, to spin, drawing in outside air and forcing it into a passage called the volute, which gradually decreases in size and terminates at the intake manifold. The greater the load on the engine, the higher the volume of exhaust and thus the more fresh air--and by extension, fuel--that is pumped into the engine, increasing output. For this reason, a turbocharger is said to be "load-sensitive," as opposed to a mechanical supercharger that provides additional horsepower according only to engine speed. When enough air is pumped into the cylinders that the pressure there exceeds atmospheric pressure, the turbocharger is said to generate "boost," which is measured in pounds per square inch (psi) in nonmetric countries. In countries using the metric system, it's measured in atmospheres, or bars; 1 atmosphere equals 13.7 psi.

The area between the hot and cold sides contains bearings, on which runs the shaft that connects the compressor and exhaust turbines. As the shaft can spin at speeds in excess of 100,000 rpm and temperatures here can top 800°F, right oil flow is critical for both cooling and lubrication. Use the proper oil--CC- or CD-rated--and change it and all filters at or before the recommended interval. Periodically inspect the area between the two chambers for signs of leakage. If the seals here fail, so will the bearing and, ultimately, the turbocharger. Occasionally visually inspect both turbines for signs of damage or excessive deposits. The hot-side turbine will normally be coated with black soot. Finally, let your engine cool down for two to three minutes at idle before shutting it down.

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