What Causes the Turbo to Leak Oil Into the Intercooler? Answered!

One common problem that turbocharged engines can experience is oil leaking into the intercooler. To get to the point, oil in the intercooler is bad because it is a sure sign of a problem with the turbo. However, there are many different causes of the turbo failing, which will result in oil collecting in the intercooler. In this article, we’ll explore the leading causes of turbo failure leading to oil leaking into the intercooler.

What a Turbo and Intercooler Does?

Turbocharger work by compressing the air sucked into the engine to increase power output. The turbocharger uses exhaust gases as they leave the engine before entering the exhaust to spin a turbine, which is why you don’t get that kick of boost until you get higher up RPMs (faster the exhaust gasses leave equals more boost). The exhaust gases drive a compressor wheel that compresses the intake air. Inside the turbo engine, oil is used as a lubricant to aid in cooling the turbo.

The intercooler is situated between the turbocharger and intake manifold, so when the air leaves the turbo, it must always pass through the intercooler before entering the engine. The intercooler cools the compressed air to increase its density, which is why you get that significant boost in performance with a turbo engine. Intercoolers are air-to-air heat exchangers, so there are no required liquids or oils inside them; so if you find oil in it, there is likely a problem with the turbo.

Why Oil in the Intercooler Is Bad

Once the oil enters the intercooler, it can mix with the compressed air and be carried into the engine’s intake manifold. This can cause a few problems.

First, the oil can reduce the effectiveness of the intercooler by coating its cooling surfaces and reducing its ability to cool the compressed air. Second, the oil can cause deposits to build up on the engine’s intake valves, reducing engine performance over time.

Finally, the oil can cause increased emissions by burning in the engine’s combustion chamber, producing smoke and particulate matter that leaks from the exhaust.

Reasons Why the Turbo Is Leaking Oil Into the Intercooler

There shouldn’t be oil in the intercooler to get straight to the point. You might see oil spots in the intercooler on a well-used engine, especially on older, higher-mileage engines. However, if you find a fair amount of oil in the intercooler, that indicates the turbo or one of its supporting components has completely failed.

As you’ll see below, most of the reasons the turbo leaks oil into the intercooler is because of a problem causing the seals or gaskets that seal the oil where its needed are leaking.

Leaking turbo seals or gaskets

If a seal or gasket fails in the turbocharger while the turbo is still spinning, the oil will be sucked into the intake side of the compressor and then into the engine via the intercooler.

You can usually spot when a turbo seal or gasket has blown just by looking at it. You will generally see oil around the intake side of the turbo (in-between turbo and air intake pipe that goes to the air filter) and may even see oil leaking or dripping from it.

Cracked turbo housing

The turbo housing does precisely as the name suggests and keeps all of the internal parts of the turbo in place. Because the housing will be cracked under pressure, the crack will open, causing pressure on seals and gaskets inside the engine, which will cause them to leak into the intake side of the turbo and flow through to the intercooler. Usually, if the turbo housing cracks, oil will be covered all around the engine bay as the leaking exhaust gasses spray it around.

If the housing cracks, exhaust gasses, and compressed air can escape, considerably reducing performance. So oil in the intercooler will probably not be the first thing you notice. But it may be if the crack is minor.

Overfilled engine oil

If engine oil is overfilled, it can cause extra pressure on the engine or turbo. Turbos require an amount of oil fed through oil lines and returned to the sump. If there is too much oil, the oil pressure inside the turbo builds as it cannot force the oil back into the engine. This stresses the seals and gaskets inside the turbo, causing oil leaks.

You may be lucky that changing or removing the overfilled oil and refilling back to the correct level may be all that’s required; however if the seals are too far gone, a rebuild or replacement may be necessary.

Blocked oil return lines

The turbo has an oil line that returns the oil to the sump, which is filtered, cooled and pushed back around the turbo. If the oil return line becomes blocked, the pressure and heat will rise in the turbo. This can result in the seals blowing and the oil leaking where it will collect in the intercooler.

Failing to change the oil at least annually is a common cause of a blocked oil return line. Old oil oxidizes, which means it becomes thick, and it will clog the oil return line, or at least the oil will not flow fast enough, causing a rise in turbo pressure.

why is the turbo leaking oil into the intercooler

Other Signs the Turbo Is Failing

If you find oil in the intercooler, you may find other signs to look for indicating the turbo has failed. They include any of the following:

Is It Normal to Have a Little Oil in the Intercooler?

No, oil in the intercooler is an excellent sign the turbo has failed. Turbos use oil to cool and lubricate bearings spinning in the turbo. However, gaskets and seals should seal the oil in the turbo. If the seals fail for whatever reason, oil finds its way into the intake side of the turbo and will be forced into the intercooler, where it will collect.

Seeing a few oil spots in the intercooler on high mileage or old vehicles is pretty normal. This is just a sign of old, worn seals inside the turbo.

How Do You Get Oil Out of the Intercooler?

Once you’ve solved the cause of whatever was causing the oil to leak into the intercooler, removing the excess oil from it is essential. If you let the oil in the intercooler, it will gradually get sucked into the engine, which will be combusted and cause more of a problem for the engine and supporting sensors.

To drain the intercooler of oil, follow the below instructions. Don’t panic if a few spots of oil remain. They will eventually get burnt away in the engine and probably won’t cause any issues.

  1. Remove the intercooler – First, remove the intercooler from the vehicle. Most cars require the removal of the front bumper, headlights, and sometimes the radiator to get the intercooler out.
  2. Drain the oil – Drain any excess oil from the intercooler by holding it at an angle and allowing it to drain. Make sure to collect the oil and correctly dispose of it.
  3. Flush the intercooler – Use a solvent, such as a brake cleaner, to flush the intercooler and remove any remaining oil. Spray the solvent into the intercooler, and hold the intercooler at an angle to allow the oil to drain out.
  4. Rinse the intercooler – Rinse the intercooler thoroughly with water to remove any remaining solvent and oil residue.
  5. Dry the intercooler – Allow the intercooler to dry completely before reinstalling it. There is no need to force rags in the intercooler to dry an hour out in the sun, and it should be pretty much dry inside.
  6. Check for leaks – Once you’ve reinstalled the intercooler, start the engine and check for boost leaks. If there are any leaks, you might hear a whistling sound of air escaping


Oil leaking in the intercooler is usually a sign the oil seals have blown in the turbo. This can be caused by several different parts of the engine or even the oil itself. Regardless of the cause, the turbo usually needs to be rebuilt or replaced, and then the oil must be drained from the intercooler before you can consider the problem entirely resolved.

My name is Tom although my friends call me Tommy. Messing around with cars and bikes has always been a hobby of mine even from a young age. So I made it my day job 17 years ago. I am a fully qualified mechanic as you would expect. I've worked in all different areas of the motor trade, valeting, panel beating, engine repairs, I'm sure you get the idea. I enjoy sharing my wealth of knowledge and experience with others, which is the reason I spend a lot of time here writing for this website.

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