Turbocharger failure: what kills one, and what the damage tells you

The corpus opens its page on the turbocharger by saying they are blamed for far more faults than they cause, and that is the right place to start — but this article is about the times one really has failed, and it has one argument:

A turbocharger almost never fails on its own. It is killed, by something else, and the wreckage says by what.

That matters commercially as well as technically. Fit a new turbo without finding what destroyed the old one and you have bought the same failure again, usually within months. The source for this article is unusually good on the first half — it is a damage-analysis guide, organised by what the broken part looks like — and says almost nothing about the second. So the appearances are kept and the consequences are added.

Why it is so easy to kill

Three numbers explain the whole subject. The shaft spins at over 100,000 rpm, the turbine side sits in exhaust gas at 700–950 °C, and the whole assembly is held up by a film of engine oil a few microns thick.

There is no ball race carrying that shaft on most turbos — it floats on pressurised oil, which is also the only thing cooling the centre housing. Interrupt the oil for a couple of seconds at full speed and the bearing is gone. Everything below is a way for the oil to be interrupted, contaminated, cooked, or for something solid to arrive where nothing solid should be.

Reading the wreckage

This is the source's material, and it is worth having in a table because the whole point is to match what you are holding to a cause.

Two of those rows are the ones an owner can actually prevent, and the source names both causes without ever turning them into instructions. So:

The two rules that keep a turbo alive

Do not switch off immediately after working it hard. The turbine is glowing and the oil pump stops the instant the engine does — so the oil sitting in the bearing has nowhere to go and nothing moving it, and it bakes onto the surfaces it was meant to protect. That is the lacquer in the table above, and it kills turbos slowly and then suddenly. A minute or two of idling after a motorway run or a hard climb is the whole fix, and it costs nothing. Cars with an electric after-run pump do this themselves; most do not.

And do not load it hard from cold. Cold oil is thick, takes longer to reach the bearing, and full boost demanded thirty seconds after a cold start is asking the bearing to run before it is fed. The source lists this as a cause of starvation and it is right. Drive gently until the temperature gauge has moved.

Between them those two habits address the majority of preventable failures, and neither appears anywhere in the original.

Oil is the whole story

Every row in that table except the two foreign-object ones is an oil problem, which makes the maintenance advice unusually simple and unusually strict:

• The specification is not a suggestion. A turbocharged engine's oil is doing bearing duty at temperatures that destroy the wrong product. Use what the manufacturer names.
• The interval is shorter than people think, and a turbo engine driven in traffic is on the severe schedule whether the handbook admits it or not.
• Use the right filter. The source names a non-specification filter as a cause of contamination scoring, which sounds like brand loyalty and is not: the bypass valve setting and the filtration rating are part of the design.
• After any engine work, prime it. Crank with the injectors or ignition disabled until oil pressure comes up before the first start, and consider filling the turbo's oil feed by hand. The first ten seconds after a rebuild is when new turbos die.

What a failing turbo does before it dies

The original stops at post-mortem, so here is the part that lets you catch it first.

• A rising siren-like whine that was not there before. The corpus notes this at loud whine or siren noise from the turbocharger, and its warning is the important one: it precedes failure, and failure sends debris into the engine.
• Blue smoke, worst just after boost or on the overrun, from oil past the shaft seals. Distinguishing this from worn rings is in head gasket failure and oil consumption.
• Oil in the intake pipework. A film in the intercooler pipes says the seals are passing.
• Loss of boost, which is where the corpus's caution belongs: P0299 for underboost is far more often a split hose, a leaking intercooler or a sticking control actuator than a dead turbo.
• Shaft play with the ducting off. A little axial float is normal; blades touching the housing is not.

Before condemning one

Check the cheap things first, in this order. The corpus is blunt that turbochargers are blamed for faults they did not cause, and the list is short:

1. Boost hoses and clamps. A split in a pipe that only opens under pressure is invisible with the engine off.
2. The intercooler and its pipework, for leaks and for oil.
3. The wastegate or VNT actuator. On a diesel the variable-vane mechanism sticks with soot, which produces both underboost and overboost depending on where it jams — and it is often freed and cleaned rather than replaced. P003A is the code for its position learning running out of range.
4. The boost control solenoid and its vacuum lines — P0045 and P0046.
5. The boost sensor itself, before believing what it reports.

P0234 for overboost deserves its own note: an overboosting engine is not a healthy engine being generous. It is usually a stuck wastegate, and sustained overboost damages pistons and head gaskets, so it is a stop-driving fault rather than a free upgrade.

And the question the merged piece answers

One of the sources folded in here compares turbocharging with supercharging, and the useful half of it is short.

A turbocharger is driven by exhaust gas that was leaving anyway, which is why it is efficient and why almost every manufacturer uses one. The cost is that it has to spin up before it makes boost — lag — and that it lives in the exhaust stream, which is where all the heat problems above come from.

A supercharger is driven mechanically from the crankshaft, so it responds instantly and makes boost at any engine speed. The cost is that it takes real power to drive, permanently, which is why it has largely lost the argument on road cars where efficiency decides.

The practical consequence for this article: a supercharger has none of the oil-starvation and heat-soak failures described above, because it is not sitting in exhaust gas and is usually not fed from the engine's oil at all. If your car has one, most of this page is not about you.

Video guides

Video, for the parts of this that are easier watched than read. The English-language ones come first.