The Guide to Your BMW Exhaust System

BMW Exhaust System

BMW is an abbreviation for Bavarian Motor Works and it was founded over 100 years ago in Germany. BMW is known for making luxury model vehicles and it has a wide range of options from the 2 Series F22 Coupe to the X5 F15 midsize crossover SUV. Whether you own a E36 3 series coupe or a brand new G30 5 series sedan, your BMW's exhaust system is an important part of its legendary performance. The exhaust system releases the gasses caused by the engine's performance and makes them less toxic.

Exhaust System Parts And How It Works

The exhaust system in your car consists of five main parts:

- Exhaust manifold

- Oxygen sensor

- Catalytic converter

- Muffler

- Exhaust pipe

The exhaust manifold is attached to the cylinder head and it removes the exhaust from each cylinder and condenses it into one pipe. The most common metal for exhaust manifold construction is cast iron, but you might also find steel, stainless steel or aluminum.

The oxygen sensor's job is to measure the amount of oxygen in your engine to allow the right ratio of fuel and air for the best fuel economy. The oxygen sensor can usually be found in the exhaust manifold or somewhere nearby in the exhaust pipe.

The catalytic converter, or cat as it's sometimes called, is a part that looks like a muffler. It's mounted on the underside of the vehicle between the actual muffler and the exhaust manifold. The cat's job is to convert the harmful gasses coming out of your engine into water vapor and carbon dioxide.

The muffler does exactly what it's name suggests. It muffles the sound of the exhaust. If you've ever wondered what sort of noise your car would make without one, just remember that the process of combustion is actually a series of explosions, which would make considerable noise without a muffler. Mufflers use baffles to allow the noise from the exhaust to bounce around and thus dissipate the energy. Mufflers may also use fiberglass to absorb sound energy.

Located between all the parts mentioned above is the exhaust pipe. Exhaust pipes are usually made of steel, but can also be made of aluminized steel or stainless steel. The latter two are better at resisting corrosion than regular steel.

Basically, your exhaust system's job is to flush out the hot waste from your engine. On the side, it also reduces engine noise and harmful emissions on modern cars. A stock exhaust can perform all these functions as needed, but performance exhaust systems can maximize your horsepower as well as make your vehicle more efficient.

Exhaust System Repair And Maintenance

Keeping your exhaust system maintained is important for good performance and good gas mileage. It's also important to ensure that the toxic gasses created by your engine's combustion are adequately carried away by a properly functioning exhaust system. So let's take a look at some common problems and maintenance.

Ultimately, the worst enemy of your car's exhaust system is corrosion, also known as rust. Rust is caused by a reaction between moisture and the iron in your steel exhaust parts, which then forms iron oxide. Moisture is, of course, a common occurrence from both internal and external sources. Obviously rain and snow are more common in some parts of the country versus others. But your car also makes moisture during combustion and that water vapor condenses and returns to liquid whenever you shut your car off. If you take a lot of short trips, the water doesn't have a chance to return to its vapor form and instead remains in the system to cause rust. A short trip can be defined as driving less than 15 miles before shutting your car off. Another rust-causing factor is places that use salt in the winter on the roads. If you drive on roads like this regularly, make sure to wash off the bottom of your car every few weeks, then run the engine to get it hot enough to remove the water.

Oxygen sensors are another part of the exhaust system that wear out over time. They typically do this in the form of being less accurate. Sometimes this causes the engine to burn more fuel than it needs to, which results in lower gas mileage. Many times a failing oxygen sensor will cause the check engine light to illuminate. Changing it every 60,000 miles or so is a good rule of thumb.

The next part to wear out is likely the muffler. Mufflers tend to rust through and the most common sign of failure is cracks, which usually alert you to their presence by your car making more noise than usual. When you do change your muffler, you should opt for a high-quality OEM muffler rather than a cheap aftermarket. With mufflers, you definitely get what you pay for.

It's rare that catalytic converters fail, but one thing that can cause them to get clogged is a faulty oxygen sensor, which is another reason to replace that part promptly when it fails. Catalytic converters are also prone to theft when located on a high-profile vehicle such as a truck or SUV. They are notoriously easy to remove. You'll generally know right away if your "cat" goes missing by the way your car runs. Symptoms of a failing cat include a loss of power, heat emanating through the floor of your vehicle and a sulfur smell. Don't let anyone tell you that your vehicle can run without a cat. Not only will you fail any emission test your state or county requires, but you could be subject to a fine as well. 

BMW Exhaust System FAQ

Q: Can I gain more power with a performance exhaust?

A: Yes, you can gain as much as 20 percent more horsepower with a performance exhaust system. It's important to understand that the exhaust system does not generate extra horsepower, but instead frees restrictions put on your engine's potential horsepower caused by the original exhaust system.

Q: Are bigger exhaust pipes better?

A: Generally yes, larger exhaust pipes are better. Auto makers tend to make smaller exhaust pipes as it's cheaper to use less metal. This naturally restricts the potential horsepower of your vehicle and makes it less efficient as well. However, don't rush out and buy the largest exhaust pipe possible for your compact car as this can have the same effect of making it less efficient. Always buy custom exhaust systems designed for your vehicle so the pipes are larger, but also the correct size for optimum efficiency and power.

Q: Is it hard to install a new exhaust system?

A: Installing a new exhaust system is a fairly straight-forward process, however it does require preparation and significant elbow grease. You'll need to actually saw off your stock pipes, so make sure to have the appropriate saw available before starting.

Q: What is a dual exhaust?

A: True dual exhaust systems have two actual separate systems, which include all normal exhaust parts. You may find them on V6 or V8 engines, but nothing smaller. There are also dual exit exhausts, but these are simply divided mufflers not dual systems.

When you need to replace or upgrade your BMW exhaust system parts, whether mufflers, headers, or catalytic converters, just visit You should always replace components of this vital system with OEM BMW parts that are guaranteed to fit your vehicle and provide performance just like the original part. Search our catalog with your vehicle info, VIN, part number or keyword. Our BMW parts experts are always available to help you find what you need or answer your questions.