How to Find and Fix Exhaust Leaks

The Role of Exhaust Systems

Before you can diagnose exhaust leak symptoms, you need to know how the system works. Your car’s exhaust system plays a simple function, which sometimes can seem complicated. The primary role of the exhaust system is to direct the gases from the combustion chamber to a safe place. In your vehicle, the safest place is outside the car, and out the back. When directed inside your car, gases from the combustion chamber can be harmful because they carbon monoxide, which is very dangerous to breath in. It is the main reason why exhaust typically exits the rear of the car, as far away from the passengers as possible.

The secondary purpose of the exhaust system is to muffle sounds from the engine and keep the driving experience quiet – which is what most consumers want. The route that the exhaust takes can be complicated, and it gets extremely hot during operating temperature. The temperatures of the system can get up to 1,200 degrees Fahrenheit the closer to the engine you get. The high and constantly changing temperatures (called thermo-cycling) cause massive stress on the components. Water is also byproduct of combustion in your car’s engine. You may never see it, except on a cold day, but water exits the system as vapor. During cold days or long times between start up, water vapor can condense within the exhaust system, which ultimately leads to corrosion. Couple this with outside elements (water, snow, salt) and you have an exhaust system that is slowly deteriorating.  

To accomplish its goals, the exhaust system requires some parts. Heat shields, pipes, mufflers, flexible joints, and unions are some compulsory features of an exhaust system. The exhaust system of your vehicle has a tough life. Thus, over time, components of it will need to be replaced or repaired. Some of the repairs are easy, while others need professional expertise.

How to Find Exhaust Leaks

Use this as a guide on how to find exhaust leak issues. The first step in repairing an exhaust leak is identifying the source of the problem. Since the exhaust pipes get very hot, a best practice if trying to isolate a leak is to do it while the vehicle is cold. Never touch the exhaust system if you have been driving the car under operating temperature. A visual inspection is the first step. Pop the hood and inspect the exhaust manifold, if you can see it. Many times, it is covered with a heat shield, but an exhaust manifold can leak in 3 areas – the mounting surface (gasket) where it joins the engine, the gasket where the downpipe, or catalytic converter attach, or the manifold itself can crack and cause a leak. Listen carefully near the top of the manifold. An exhaust leak typically sounds like a sharp in-rhythm “tick” sound. Many people confuse an exhaust leak at the manifold with an engine knock, or lifter noise, but often times, it’s an exhaust leak. If the ticking sound appears to be lower down on the engine, it’s likely the flange gasket connecting the manifold to the down pipe, or catalytic converter. It’s best here to put the vehicle on ramps and remember – check only with the vehicle cold! Listen and inspect where the exhaust pipe has connections. Since the vehicle is cold, you can carefully take your hand and feel the air around the pipe connection. Remember, don’t touch! If there’s an exhaust leak, you will feel the air pulsing out of the leak.

Under the car, there are several common exhaust components that can fail. Many vehicles have what is referred to as a flex-pipe in the exhaust system. This pipe has a flexible metal interior, similar to an accordion, with a woven, stainless steel fabric around out. Over time, these flex-pipes fail and can leak. A failed flex-pipe is easy to spot and creates a good deal of exhaust noise. Another common failure is flexible flange joints. Flange joints where were 2 pieces of exhaust pipe are joined together. A non-flexible joint uses a gasket between the two flat flanges to bolt together and make a seal. While these can fail, they are not as common as flexible joints for failure. The majority of flexible exhaust joints use a spring flange with a large “donut” gasket, which allows for flexing as the car moves. Many times, these flexible joints fail, and often times, it’s the donut gasket that deteriorates. Other common failure points are the muffler and catalytic converter. Check for any holes or sections where the muffler has rusted through, or has come apart. Often times, a catalytic converter will fail because the honeycomb element inside of it breaks apart, and begins to rattle. Resonators, which are essentially a secondary muffler farther down than the initial muffler, can also fail, rust, and break open.  As you carry out the inspection, pay close attention to the exhaust pipe and look for any broken rubber hangers, or pipe that has a considerable amount of rust. Most OEM exhaust systems in the last 15 years are made from stainless steel now, but some are not. If you see heavy rust in particular areas on the pipe, these areas may be suspect for failure soon. You can take a pair of large pliers and gently squeeze those areas – if the pipe flexes or compresses – it is very thin and needs attention. On any areas, a common sign of an exhaust leak is black soot. If you see it on any connection, or any areas of the pipe, muffler, or other components, there is a leak.

Symptoms of an Exhaust Leak

The exhaust system works for you and your car’s safety. If damaged, the dangerous fumes from your car’s exhaust system can leak into the passenger cabin. You could be at risk of inhaling poisonous gases. If you suspect a leak in your car’s exhaust system, don’t hesitate to visit an auto repair shop. When you know what to look for, you can manage the exhaust leak repair. Here are common exhaust leak symptoms:

• When the exhaust of your car is leaking near the manifold, the efficiency of your vehicle could decrease by 3-4 mpg. This can happen because the leak bypasses the sensors that read incoming and outgoing oxygen. Thus, an excessive amount of fuel is burned. To maximize your fuel economy, fix any exhaust system leaks immediately. 
• If you a tapping, ticking, or raspy noise under car or in front of you in the engine compartment as you accelerate, your exhaust pipe could be leaking. Since the fumes escape at high velocity, even minor leaks will cause a noise, or worse yet, vibration. More significant leaks will cause worse vibrations. The vibrations can be felt on the floorboards and the steering wheel and will be more pronounced as you accelerate harder. 

How to Fix Exhaust Leaks

If you discover an exhaust leak from the manifold or the joints, you can seal the leaks by changing out the failed gasket. Every joint that is made to be separated on the exhaust system has some form of a replaceable gasket. Keep in mind, the nuts/bolts that hold these joints together can be extremely rusty, making it a hard task to remove them. It’s a good idea to pre-soak any bolts in penetrating oil – usually a day before you plan on working. Keep in mind that exhaust bolts can have a tendency to break, so when loosening, if you begin to feel heavy resistance, switch to tightening the bolt by ¼ turn, spray a bit of penetrating oil, and loosen again. Continue this process slowly back and forth if you encounter any resistance.

When fixing any leak at a joint – especially a flexible joint with a donut gasket – make sure that the area and sealing surfaces are completely clean. Often times, old gasket material is difficult to remove, and will need a good scraper or wire brush to completely remove. When removing gasket material in a ball/cup style flex flange, using a wire brush that attaches to a drill works well to clean and smooth this area.  

When you encounter the need to replace a muffler, resonator, or catalytic converter, some of these items can be clamped into place or bolted with a flange, but often, they are welded into place. Many times, even clamped items can be difficult to remove and need to be cut out with a reciprocating saw or hack saw to remove. If the need is there to insert an adapter, hanger, clamp, or expand the pipe you’re working with, AutoZone carries the parts and Loan-a-Tools to accomplish this. Remember, if you are in doubt – seek out a quality repair shop to help assist.

Epoxy bonds and tapes can also be used to temporarily fix exhaust leaks. However, before applying them, clean and smooth the leaking surfaces. An aluminum patch will toughen the epoxy bonds. Once you are through, wrap the area with exhaust tape. Keep in mind, many of these repairs may last some time, but they are all meant to be emergency repairs. Replacement of the component will be necessary.

If you suspect a leak in your exhaust system, have it checked right away for your car’s safety and your health. Exhaust fumes are dangerous when they get into the passengers’ cabin. They can result in significant health risks. At AutoZone, we sell all the parts you need to properly repair your exhaust system, purchase new parts, and get quality advice on the repair.