My Turbocharger Seals Are Leaking Oil — Or Are They?

It’s one of the most common — and misunderstood — diagnoses when troubleshooting a turbocharger.

Oil is found in the compressor or turbine side of a turbocharger and the immediate conclusion is often:

“The turbo seals are leaking.”

But it’s not quite that simple.

A turbocharger does not use conventional oil seals in the way they are often described. What is commonly referred to as a turbo “oil seal” is actually a steel sealing ring, similar in design to a piston ring.

What does the sealing ring actually do?

The sealing ring’s primary function is to prevent pressurised air from the compressor side and exhaust gas from the turbine side from entering the turbocharger’s bearing housing and oil system.

In other words, its job isn’t simply to act as a barrier that “holds the oil inside” the turbocharger.

Under normal operating conditions, the turbocharger’s oil supply and drain system manages the flow of oil through the bearing housing. The turbocharger therefore does not rely on these sealing rings to prevent oil leakage in the same way a conventional oil seal would.

A closer look at the steel sealing ring fitted to the turbocharger assembly.

So why is there oil in my turbocharger?

Finding oil on the compressor or turbine side does not automatically mean the turbocharger has failed.

Oil can pass through an otherwise serviceable turbocharger when the correct operating conditions around the turbo are disrupted.

Possible causes include:

• Excessive crankcase pressure or engine blow-by

• A restricted, damaged or incorrectly installed oil drain

• Incorrect or excessive oil pressure

• An overfilled engine oil level

• Intake system or air filter restrictions

• Exhaust system restrictions

• Other engine or installation-related issues

These conditions can affect the pressure balance and oil drainage within the turbocharger, allowing oil to appear where it normally wouldn't.

Before replacing the turbocharger

If oil is found in the compressor or turbine housing, don't assume that replacing the turbocharger will solve the problem.

The underlying cause should be identified first. If an external engine, lubrication, intake or exhaust issue is responsible, fitting another turbocharger without correcting that issue may result in the same problem occurring again.

Correct diagnosis can prevent an unnecessary turbocharger replacement — and help ensure that a replacement turbo isn't blamed for a problem originating elsewhere in the system.