As part of the exhaust system, the exhaust manifold plays a supporting role in the engine compartment. If the exhaust manifold is leaking, the exhaust gases of the engine are not discharged as intended. The function of the engine can also be restricted if the exhaust manifold is leaking. In our guide, we explain the signs and causes of a defective manifold and give tips on how to replace the component.

Manifold carries exhaust gases away from the engine

The exhaust manifold removes the exhaust gases produced during combustion from the engine. Here, the manifold acts as a connection between the cylinder head and the exhaust system. The combustion gases emitted by the cylinders are collected by the exhaust manifold and passed on to the exhaust via other components of the exhaust system. This is where the exhaust gases are emitted.

Exhaust manifold is a well thought-out component

However, the component, also known as the exhaust manifold, does not simply remove exhaust gases. They are thoughtfully designed components that even have an influence on engine performance. For this purpose, the manifolds are specially adapted to the respective type of engine. Exhaust manifolds are made of special cast iron or stainless steel pipes.

Arrangement of pipes and use in turbo engines

If an engine has more than one cylinder, the exhaust manifold brings together the different exhaust flows. The arrangement of pipes and the order of merging can differ depending on the type of engine. In an engine with a turbocharger, the exhaust manifold does not direct the exhaust flow directly to the exhaust, but first to the turbo.

Exhaust manifold leaking – change or repair?

Exhaust manifolds often break down due to high stress. If the exhaust manifold is leaking, the question sometimes arises: Replace or repair? In principle, a cracked exhaust manifold can be repaired. To repair it, the manifold often has to be removed from the car. Welding the manifold requires a certain amount of experience. Often, the cost of repairing the manifold in the workshop is not worth it, as exhaust manifolds are readily available new or used.

Typical symptoms of a defective exhaust manifold

A problem with the exhaust manifold leads to the appearance of typical symptoms. These include the escape of exhaust gas into the engine compartment, as the exhaust gases are no longer diverted to the exhaust. This in turn is often the cause of the car smelling of exhaust fumes in the interior. Under unfavourable conditions, these are drawn into the vehicle interior through the ventilation.

Traces indicate leaking manifold

Damage to the manifold is often indicated by clear traces of exhaust gas. This makes it easy to see where the exhaust manifold is leaking. There is also often an unusual noise from the engine when there is a problem with the manifold. Exhaust gas leakage can also cause a loud whistling noise when accelerating.

Power loss due to cracked manifold

In addition to these unpleasant symptoms, a defect in the exhaust manifold also has a direct influence on the function of the engine and exhaust system. Particularly with turbo engines, engine performance can drop noticeably if there is damage to the exhaust manifold. In addition, fuel consumption can increase and acceleration can drop noticeably with a defective manifold.

Symptoms of a defective manifold in overview:

• Traces of escaping exhaust gas
• Noises from the engine compartment
• Smell of exhaust gas in the vehicle
• Engine power decreases
• Fuel consumption increases
• Acceleration is poor
• Engine control light up

Common causes of leaking exhaust manifolds

If the exhaust manifold is leaking, there are various possible causes. The exhaust manifold is one of the most thermally stressed components of the exhaust system. The hot exhaust gases cause the manifold to heat up strongly when the engine is running, which can lead to wear over time. In addition, there are strong temperature fluctuations in the engine compartment.

Vibrations and weather influences

The vibrations generated by the engine can also have an influence on the service life of the exhaust manifold. In addition, damage to the exhaust manifold can be caused by weather conditions, as the component is positioned quite unprotected in the lower area of the engine compartment, depending on the vehicle. Last but not least, the exhaust manifold can be damaged as a result of unprofessional repair of the exhaust system.

Overview of common causes for leaking exhaust manifolds:

• Temperature fluctuations during operation
• Wear with high mileage
• High temperature of the exhaust gases
• Damage due to weather influences
• Exhaust manifold repair
• Exhaust manifold cracks due to vibrations

Changing the exhaust manifold

The exhaust manifold should be replaced promptly with an intact component in the event of damage such as a crack in the pipe. This will ensure that the car continues to function properly. In addition to unpleasant effects such as the poor running of the engine, emissions can also enter the interior instead of the exhaust and thus pose a danger.

In addition, the exhaust gas purification system often does not function correctly if the exhaust manifold is leaking. Practised and expert car mechanics sometimes change the manifold themselves in order to save costs for the workshop. The exact procedure can vary depending on the engine and model.

The seal is also a possible cause

If symptoms of a defective exhaust manifold appear, the component itself does not necessarily have to be defective. The manifold gasket can also be the cause of unusual noises and the escape of exhaust gases even before the exhaust pipe. The gasket can usually be purchased at low cost and can be easily installed by the owner or in a workshop.

Changing the exhaust manifold in just a few steps

1. Prepare the replacement of the manifold: The first step is to prepare the replacement of the defective exhaust manifold with an intact spare part. Depending on the vehicle model, various attachments and covers in the engine compartment must be removed in order to be able to replace the exhaust manifold.
2. Removal of the defective part: If everything is well prepared, the removal of the defective exhaust manifold can begin. On many vehicles, this can be done from above through the engine compartment. As a rule, parts of the exhaust system as well as the exhaust pipe must be removed. After loosening the screw connections on the engine stud bolts, the exhaust manifold can be removed.
3. Install the exhaust manifold: The next step is to install the intact exhaust manifold. To do this, the component is installed as intended. In any case, a new manifold gasket should be used. Nuts, screws or stud bolts can also be replaced if necessary.
4. Complete the repair: After installing the manifold, the other components of the exhaust system and all add-on parts are reassembled. A test run of the engine can then take place.

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