Diesel power is limited by how much clean air reaches the cylinders and how effectively fuel mixes with it. Naturally aspirated engines draw air at close to atmospheric pressure. Turbocharged engines use exhaust energy to compress more intake air. A charge-air cooler may reduce its temperature and increase density.
Air restriction, boost leakage, exhaust restriction or a damaged turbo can all reduce available air. The result is often black smoke, poor acceleration and inability to reach normal rpm. Before condemning the turbo, inspect the air filter or silencer, intake hose, hose clamps, charge-air cooler, exhaust elbow, propeller load and fuel delivery.
Turbochargers operate at very high speed and temperature. Clean oil supply and an orderly shutdown after hard running matter. Do not touch compressor blades, run the engine with guards or intake components removed, or spray flammable cleaner into a running intake.
Oil film in intake plumbing can be normal in some crankcase ventilation arrangements. Pooling oil, rapid consumption, blue smoke or uncontrolled acceleration is not normal. An engine ingesting lubricating oil can run even after normal fuel is shut off. See engine runaway and emergencies.