Turbo

Your turbocharger did not die on its own

A turbocharger is in principle a simple machine: two wheels on one shaft, carried on oil-film bearings. Even so it is one of the parts that most often fails on a modern diesel.

The explanation is that it works under conditions no other component in the engine is exposed to. The turbine wheel sits directly in exhaust gas at up to 900 degrees, while the shaft rotates at up to a quarter of a million rpm — around 4,000 times a second.

The shaft never touches the bearings. It floats on an oil film thinner than a hair. The entire service life of the turbocharger depends on that film never breaking down.

The four causes — and where they sit

Oil starvation or delayed oil supply. A blocked oil filter, a crushed oil feed pipe, coking in the return line, or simply a start after a long period standing with no oil pressure. If the film breaks down at that speed, it takes seconds, not kilometres.

Oil contamination. Soot and metal particles in the oil act as an abrasive in the bearings. That is why a new turbocharger on an engine with postponed oil changes dies again.

Foreign objects. A piece of an air filter, a nut, a broken valve guide. The compressor wheel blades are thinner than a millimetre at the edge.

Overspeed. A leak in the intake after the turbocharger, a faulty VNT mechanism or an incorrect software tune makes the turbo run faster than it was designed for. At some point the material gives up.

That is why we strip it before quoting

Every cause of failure leaves its own signature. Oil starvation looks different from foreign object damage, which looks different from overspeed. By reading the damage pattern we can tell you what went wrong — including when the answer is that the problem has to be fixed elsewhere on the engine.

Skip that and simply fit a new unit, and the next turbocharger goes the same way within a few thousand kilometres. And then the customer believes the workshop’s work was at fault.

Short trips wear harder than long ones

That surprises many people. But on short trips the engine never reaches operating temperature, the oil never burns off condensation and fuel, and after a hard pull the turbo sits glowing and stationary while the oil in the housing cokes. Those deposits slowly block the oil passages.

A vehicle that covers 15 kilometres to work and 15 home is harder on its turbocharger than one driven on the open road every day.