TURBOCHARGER LUBRICATION (SOAKBACK) SYSTEMPrior to the engine startup, a soakback pump lubricates the turbocharger. Oil is drawn from the engine oil sump and passesthrough a soakback pump filter (figure 4, item 7). Oil is then supplied to the turbocharger through external piping, which isconnected to the engine-mounted filter housing. In operation, the turbocharger is lubricated by the main oil pressure pumpof the main lube oil and piston cooling oil pump (figure 4, item 1) through internal passages within the engine. Beforeentering the turbocharger, the oil passes through an engine mounted turbocharger filter (figure 4, item 5).To ensure lubrication of the turbocharger bearings prior to the engine start and the removal of residual heat from the turbo-charger after engine shutdown, a separate lube oil pressure source is provided. This pressure is controlled automaticallythough the engine START and STOP controls. An electrically driven pump drawing lube oil from the oil pan pumps the oilthrough a soak back oil filter and the head of the turbocharger oil filter directly into the turbocharger bearing area. Themotor driven pump and filter are located on the starboard side of the engine.A pressure relief valve set at 379 PSI (26 bar) is located in the head of the turbocharger oil filter (figure 4, item 5). When theengine starts, and while the motor driven pump is still running, main lube oil pressure from the engine-driven pump becomesgreater than the motor driven pump pressure. Since there is no outlet for the lower pressure oil, the relief valve will openwhen the pressure builds up to 379 PSI (26 bar), and the oil will return to the pan through a passage in the turbocharger oilfilter head mounting flange. Also located in the turbocharger oil filter head is a bypass valve, set at 483 PSI (33 bar). Thisvalve will open to permit motor driven pump pressure to bypass a plugged filter element so that lubrication can be suppliedto the turbocharger to prevent turbo damage.TURBOCHARGER OIL FILTERThe turbocharger oil filter (figure 4, item 5) provides additional protection for the high-speed bearings and other lubricatedareas of the turbocharger by filtering the oil just before it is admitted to the turbocharger. Oil enters the filter through a castmanifold and, after passing through the filter, returns to the upper idler gear stubshaft and into the turbocharger. The filterelement is pleated paper construction, and is disposable. The filter is mounted on the camshaft drive housing at the rightbank of the engine.0017 00-6.

As can be deduced, there are two oil filters. The first one filters the oil from the standard engine sump. The second filters the oil used by the turbocharger.

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Note added at 3 hrs (2007-11-15 21:57:01 GMT)
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The turbocharger is a turbine.