The trouble with a whistling turbo

Even a turbocharger in excellent condition makes noises! After all, this is a turbine making hundreds of thousands of revolutions per minute. The background noise associated with the ensuing flows is therefore completely normal. However, the intake lines and air filter housing have been designed in such a way that normally the driver hears almost nothing from the turbo. If a new turbocharger attracts the driver’s attention immediately after installation because of sounds such as whistling, rattling, or rasping, the defect can usually be found in the turbo’s periphery.

Noises can be caused by the following.

1. Something isn’t leakproof — fault source #1

Leak on the charge air side:

If a turbocharger is replaced after thousands of kilometers, the charge air pipes connected to it must also be removed or decoupled during the repair. The flanges normally contain sealing rings, which have been pressed into position over many years. If you open the joints and then put them back together again, this old, deformed seal becomes unusable. The charge air escapes, resulting in whistling and hissing. However, a stone chip in the charge air cooler will also manifest itself in this way. And the escaping boost pressure also reduces the vehicle’s power output.

Leak on the exhaust side:

The exhaust gases leave the engine at a very high speed and several bars of pressure.

If a used metal gasket is reused—e.g., on the manifold flange—exhaust gases can easily escape at this point. But even the best gasket is of little use if the flange areas are warped or heavily clogged. In the case of bigger leaks, power losses may occur, as insufficient exhaust gas arrives at the turbocharger’s turbine. As a result, the boost pressure falls.

Therefore: always replace metal gaskets and sealing rings, fix all leaks, check manifold and flange for distortion, and remove contamination from sealing areas.

2. Blockbuster: How to prevent blockades

If the turbocharger gets too little air, it will start making noises. If, for example, the air filter is not checked thoroughly and replaced regularly, the intake resistance increases substantially. In the worst case, the rotor assembly shifts axially, causing the impeller to brush against the housing—a phenomenon you can’t fail to hear!

It’s exactly the same on the other side: if the exhaust gases accumulate here and cannot flow freely out of the cylinder, disturbing flow noises will soon be produced ( see TM 03/2016). Incorrectly mounted gaskets can also cause a bottleneck in the exhaust gas system.

Therefore: always replace the air filter when changing the turbocharger and keep an eye out when replacing gaskets.

3. Ringing alarm bells: foreign objects in the turbocharger

A foreign object in the turbocharger—and it’s already ringing in your ears! On the exhaust side, pieces of the manifold that have broken off can grind against the turbine wheel. This causes an imbalance in the rotor assembly, the shaft breaks, and the turbocharger suffers a total failure!

Of course, foreign objects also lead to serious problems on the compressor side. Whether it’s loose nuts from previous damage ( see TM 07/2016) or other objects that hit the impeller, damage is inevitable!

Even if the vanes of the compressor are “only” bent, this can still cause significant flow noises during operation.

Therefore: always check composite or multipiece welded manifolds for internal damage. Open intake lines upstream of the turbocharger and remove foreign objects if necessary.