Exhaust Manifold: Operation and Maintenance

Designed to carry the exhaust gases produced by combustion, the exhaust manifold is an essential part of your engine. It is located at the outlet of the exhaust valves, where a chamber channels the gases into the exhaust pipe.

What is the purpose of the exhaust manifold?

As the name implies, the exhaust manifold collects the exhaust gases directly from the engine. Since exhaust gases can reach 800°C when they leave the engine, the manifold must be able to withstand high temperatures. For this reason, it is usually made of high-strength steel.

Located at the outlet of the exhaust valves, the exhaust manifold consists of one pipe per cylinder. All of these pipes come together in a single common chamber, allowing the exhaust gases to be routed to the tailpipe.

In addition to temperatures, the exhaust manifold must withstand the pressure of the gases leaving the combustion chamber (between 2 and 3 bars). For this reason, it is equipped with a manifold gasket to prevent leaks.

4 types of exhaust manifold

Nowadays, exhaust manifolds can be found on all types of vehicles and their complexity varies according to the number of cylinders.

• Some engines have only one cylinder (motorcycle engines, for example). In this case, there is no real need for an exhaust manifold, as a single pipe is sufficient.
• Multicylinder engines usually have one pipe per cylinder, and the manifold allows them to be grouped.
• Four-cylinder inline engines have a slightly different configuration due to the firing order of the cylinders. Cylinders 1 and 4 are brought together, as are cylinders 2 and 3, and then the two outlets are brought together again.
• On top-of-the-range or sports cars, the number of cylinders can be very high, and therefore we find much more atypical manifold configurations, since there are many factors to take into account (firing order, cylinder layout, crankshaft shape, etc.).

In practice, manufacturers mainly design the exhaust system and manifold based on the layout of the engine and chassis. This is because the front suspension and steering system reduce the space available for the exhaust manifolds.

Modern compact cars have little space in the engine compartment, so manufacturers install very small and compact exhaust systems and manifolds in these cars.

Exhaust manifolds are designed to minimize the overlap of exhaust strokes, which in turn minimizes back pressure. OEMs often achieve this by dividing the manifold into two or more bifurcations. This prevents two cylinders from exhausting into the same branch at the same time.

Flow restrictions are eliminated by increasing the capacity of the exhaust manifold and incorporating large-radius elbows into the design. This also reduces back pressure.

What are the symptoms of a worn exhaust manifold?

There are a number of symptoms that can alert you to a faulty exhaust manifold:

• Abnormally loud engine noise;
• Loss of power and acceleration;
• Excessive fuel consumption;
• Emission of a burning odor;
• Exhaust manifold reddening;
• Exhaust manifold leaks.

If you are experiencing any of these symptoms, don't delay in visiting an auto repair shop to have your exhaust system checked.

How do I replace an exhaust manifold?

Want to change your exhaust manifold yourself to save on car maintenance? Follow the steps in our tutorial to replace your exhaust manifold. This is a tricky operation and should only be done by experienced mechanics.

Step 1: Put the car on jacks

Start by disconnecting your car's battery so you can work safely. Continue by jacking up your car.

Step 2: Remove the heat shield

Next, remove the bolts securing the heat shield, which protects your car from the high temperatures generated by the engine.

Step 3: Remove the exhaust manifold fasteners

Once the heat shield is removed, you can unscrew all the bolts and screws that secure the exhaust manifold. Don't hesitate to use degreaser if necessary to make it easier to remove the fasteners. Do not forget to remove the screws that secure the exhaust pipe to the underside of the car as well.

Step 4: Remove the exhaust manifold

Once the exhaust manifold is no longer attached to the cylinder head bolts and the exhaust pipe, you can finally remove it, taking care not to damage any other parts of the engine.

Step 5: Remove the manifold gasket

Once the exhaust manifold is removed, you will have access to the exhaust manifold gasket. This gasket can be discarded as it must be replaced at the same time as the exhaust manifold to ensure it remains watertight.

Step 6: Replace the Exhaust Manifold

You can now install the new exhaust manifold, carefully following all the previous steps in reverse. Be sure to position the new exhaust manifold gasket correctly to avoid any leaks.

How do I clean my vehicle's exhaust manifold?

Like all exhaust components, the exhaust manifold is exposed to soot and harmful particles from exhaust gases. It will eventually become clogged with time and repeated driving. Before removing it, try exhaust cleaning products.

If your manifold is already too clogged or eaten away by rust and carbon, you can try cleaning it. Start by jacking up your vehicle on stanchions or a bridge. You'll need safety glasses, gloves, and of course some degreaser.

1. Remove the exhaust manifold: To effectively clean the exhaust manifold, it is often necessary to remove it from the engine. To do this, we recommend you consult your vehicle's service manual, as each manifold has its own peculiarities. To work in peace, don't forget to disconnect the battery. Then remove the screws that hold the heat shield (which protects your car from the high temperatures generated by the engine).
2. Loosen the screws and fasteners on your manifold and exhaust tube. Carefully remove the exhaust manifold from the cylinder head bolts, then remove the exhaust manifold gasket. Don't hesitate to take a photo of the disassembly to facilitate the reassembly.
3. Clean the exhaust manifold: There are several ways to clean an exhaust manifold, including using an exhaust system cleaner or a strong degreasing product. It is important to choose a product that is compatible with the material of the exhaust manifold, which can be steel, cast iron, stainless steel or aluminum. Apply the product to the manifold and allow it to work according to the manufacturer's instructions, then rinse thoroughly with water. If it's rust that's damaging the manifold, try using a cloth soaked in white vinegar or even soaking the entire part. Otherwise, as with lambda sensor maintenance, gasoline can be used as a cleaner. It's simple and effective, as long as it's thoroughly rinsed and dried.
4. Use cleaning tools: If the exhaust manifold is very dirty, it may be necessary to use cleaning tools such as wire brushes, scrapers or sanding discs to remove stubborn residue.
5. Reassemble the exhaust manifold: Once the exhaust manifold is clean and dry, it can be reinstalled on the engine following the instructions in the service manual.

However, it is important to note that cleaning an exhaust manifold can be a difficult and time-consuming process, and it is often more effective to replace the manifold if it is severely damaged or clogged.

Need to replace your exhaust manifold? Using MOSTPLUS is still the easiest way to save money on exhaust maintenance!