Diesel Turbo Failure: Symptoms, Causes and When to Rebuild

The turbo is a part that spins at tens of thousands of revolutions per minute, withstands very high temperatures on the exhaust side and depends entirely on engine oil. That is why most of its failures can be prevented, and nearly all of them give warnings before breaking. This guide explains what they are, what causes them and when a rebuild makes sense.

What does a turbo do?

A turbocharger uses exhaust gas to spin a turbine, which in turn drives a compressor that pushes more air into the engine. With more air, more fuel can be burned per cycle and more power is obtained without increasing displacement. In diesel engines, which run with excess air, the effect is especially noticeable.

The rotating assembly rides on a film of oil that lubricates and cools it, and that dependence on oil explains almost all of its failures.

Symptoms of a failing turbo

Blue or gray smoke

It indicates oil passing through the seals toward the intake or exhaust. Sometimes it is caused by a blocked drain that prevents oil from returning to the sump. See black, white or blue smoke.

Abnormal whistle or siren sound

A whistle higher pitched than normal can indicate a compressed air leak in the hoses or excessive shaft play. A metallic, scraping sound suggests the wheel may be touching the housing and calls for stopping the engine.

Loss of power

If the turbo does not generate the expected boost pressure, less air enters and the engine loses power, with black smoke. On variable geometry turbos, carbon can leave the vanes stuck. See why a diesel loses power.

Oil consumption

An oil level that drops between changes with no visible leaks can point to worn turbo seals.

Oil or debris in the intercooler

If a hose comes off with a lot of oil or metal particles inside, the turbo is passing oil or has shed material.

Most frequent causes of failure

• Lack of lubrication: low oil level or insufficient pressure, especially at start-up.
• Contaminated or degraded oil: old or dirty oil wears bearings and shafts. Following oil change intervals is key.
• Blocked turbo drain: oil does not return and builds up.
• Particles entering through the intake (poor air filter) or exhaust.
• Carbon on variable geometry vanes.
• Shutting off a hot engine immediately after demanding driving.
• Actuator or wastegate faults that cause overboost.

What is checked on a turbo?

Rebuild or replace?

If the housings and main components are not damaged, the turbo can be rebuilt: it is disassembled, bearings, seals and damaged components are replaced, it is cleaned and the rotating assembly is dynamically balanced. That balancing is essential: a minimal imbalance at those speeds destroys bearings in a short time.

If there is severe damage to the turbine or housing, replacement may be more reasonable. In both cases, the most important point is this:

How to extend turbo life

• Change oil and oil filter at the recommended intervals.
• Keep the air filter in good condition.
• Let the engine idle a few seconds after demanding driving.
• Do not floor the throttle with a cold engine.
• Deal promptly with any whistle, blue smoke or oil consumption.

To see how these parts are handled, read about the turbochargers service.