Exhaust leaks are a part and parcel of owning an older vehicle. Years of exposure to road salts and rain don’t treat the exhaust system too kindly. Because of that, the exhaust is usually the first to show signs of trouble.
Given enough time and right environmental conditions, you’ll experience an exhaust leak somewhere. However, finding where the leak is can be tricky. Here’s a general guide on what to look for, where to look first and how to get on top of exhaust leaks if you find one on your car.
Anatomy of an Exhaust System
Car exhausts come in all different flavors, but most of them consist of a common set of components. Everything that makes your exhaust is there for a reason and performs a certain function.
Above is a diagram of your average exhaust. Note that this is just a simplified representation. The piping is rarely as straight, while cars with V engines usually have two of everything. That said, let’s start from the top.
Exhaust Manifold/ Header
Once the engine completes the compression cycle, it needs to evacuate the leftover gases from the combustion chamber. As the piston enters the next stroke, exhaust valves open, and the fumes are pushed out.
The exhaust manifold is there to take the leftover gases and move them efficiently away from the engine. It’s usually a solid piece made of cast alloy steel designed to take on the brunt of the force of the escaping gases.
Car manufacturers sometimes place catalytic converters on the manifold itself in an effort to save space.
Alternatively, you might find a header instead of an exhaust manifold. Their purpose is essentially the same. The main difference is that headers are designed to improve the flow of gases away from the engine, which is most often done through the use of longer pipes and a more complex design. There are 4-1, 4-2-1, and 3-2-1 headers out there, among others, depending on the design of that particular engine.
O2 Sensor
Most cars have two O2 sensors installed at various points along the exhaust system. You’ll often find the first O2 sensor on the manifold, or on the downpipe sitting right after the manifold. Check your car’s manual to find out the exact location of your O2 sensors — it’s good info to have moving forward.
Downpipe
Now that the gases have been evacuated from the engine, you need a way to push them down under the car and toward the rear. If your car has a standard exhaust manifold, the downpipe bridges the gap between it and the catalytic converter.
With a header, there may not be a downpipe in the classic sense, as these often extend all the way down underneath the car. In this configuration, a downpipe may just be a small piece of piping connecting the header to the catalytic converter.
Flex Joints
The flex joint is used to connect the downpipe or headers to the catalytic converter. This piece of the exhaust is made to be flexible (hence the name) and is wrapped in a metallic mesh. The flex joint or flex pipe allows the rest of the exhaust to move without affecting the exhaust manifold/header.
Catalytic Converter
With the evolution of ecology as a science, car manufacturers were forced to do something about toxic gases produced during combustion. The solution came in the form of a catalytic converter.
This device uses a honeycomb structure made of metals such as platinum to filter out toxic substances in the exhaust gases, thus reducing the overall carbon footprint of the car. Catalytic converters are usually followed by another O2 sensor that measures the amount of oxygen in the post-cat fumes. This data is then used by the ECU for various purposes.
Muffler
Next comes the muffler, which is usually a large piece found near the rear of the car. The muffler’s job is to silence the exhaust system.
Tailpipes
A tailpipe is the final piece of the exhaust system which is what you see when you’re looking at the back of your car. This is a purely aesthetic piece of the system that doesn’t do anything as far as performance or sound goes.
What Causes Exhaust Leaks?
Most exhaust leaks are caused by exposure for the most part. Given enough time, road salts, rainwater, and moisture in, in general, will eat away at the metal, causing oxidation that usually leads to structural damage. It doesn’t help that car manufacturers are doing their best to make exhausts as cost-efficient as possible.
One thing that can speed up this process is physical damage. If you’ve ever beached your car, or if you drive a lowered car that scrapes a lot, that could cause damage which makes that particular section of the exhaust more prone to springing a leak.
Gasket Exhaust Leaks
That said, a decent portion of exhaust leaks occur in areas where two pieces of the system are joined together. It’s not uncommon for the exhaust manifold gasket to fail, causing a substantial leak right outside the combustion chambers. The same goes for any other gasket along the line. Inspect your gaskets and replace them when necessary. Check out our selection of exhaust gaskets and other exhaust system components.
How to Find Exhaust Leaks On Your Car?
Finding exhaust leaks can be easy or annoyingly difficult depending on the size of the leak and where it’s located. That said, the process is more or less the same.
Get a general idea of where the leak is, inspect that particular section of the exhaust, and locate the leak. If you’re dealing with a smaller leak, there are a few things you can do to help amplify the noise. Let’s start from the beginning.
Inspect the Exhaust System
Let’s assume that you’ve noticed that your exhaust is much louder than it usually is. Let’s also assume that you can’t really tell where the sound is coming from. The first thing you’d want to do is jack up the car so that you can visually inspect every section of the exhaust. Get the car on jack stands and make sure that it’s secure. Don’t use a floor jack to hold the car in the air while you’re working under it. That can end badly.
Now that you have a good view of your car’s underbelly, start from the rear and work your way toward the downpipe. You’re looking for anything obvious, such as larger rust spots on any of the components.
If you’re not seeing any, look for soot spots. Usually, when there’s a leak, the escaping exhaust gases will soot up the surrounding area. The tricky part is finding such spots on the top of the piping. Fortunately, leaks rarely occur on the top area of the exhaust as such areas are shielded from the elements.
Use the Rag Trick
One way to amplify the sound of a very small leak is to stick a rag into the tailpipe. This will force the exhaust gases to find another way out, which is usually the spot that’s leaking. You’ll need an assistant to plug the tailpipe while you’re looking for the exhaust. Just to be on the safe side, don’t keep the rag in there for too long at a time.
Soapy Water and Leaf Blower/Compressor Method
Another way to go about doing this is to use soapy water in combination with a pressurized exhaust system. Make sure that your engine is nice and cold while you’re doing this. Find a way to introduce air to the exhaust at the tailpipe by using a compressor or a leaf blower. Then, take a spray bottle full of soapy water and start spraying suspect spots. What you’re looking for are bubbles.
This is a great method of finding leaks that originate at or around the exhaust manifold, flanges, joints, O2 sensor points and similar areas.
How to Fix an Exhaust Leak?
Depending on where the leak is, and what’s causing it, a fix can be anything from tightening a bolt or replacing an entire section of the system with a brand-new part. This varies wildly depending on the location and severity of the leak. The absolute best way to handle a leak on a pipe somewhere is to weld a new section in.
That said, there are various types of sealants and putties you can use as a temporary solution or a permanent one in case of a small leak. One thing to keep in mind is that exhaust manifold leaks usually mean that there is a crack in the manifold itself. At that point your only real solution is to replace the whole thing. Check our selection of exhaust manifolds for good replacement options.
Hole In The Muffler?
Chances are that you’ve noticed a small hole at the bottom of your muffler during your inspection. That’s a drainage hole designed to let the water out of the muffler. Whatever you do, don’t seal this hole. In fact, check if it’s obstructed by debris.
Find Exhaust Leaks, But Do It Safely!
We’ll end this guide with a short safety PSA. Use jack stands, make sure that your car is on flat ground, and check that the car is stable by giving it a side-to-side push. Don’t work under the car unless you’re 100% sure it’s going nowhere. If you need parts for your car, check our catalog for quality options. We stock exhaust pipe seals, exhaust clamps, and more for all kinds of vehicles.
