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Exhaust Leak Diagnosis

Dan Ferrell writes about do-it-yourself car maintenance and repair. He has certifications in automation and control technology.

Ford Escort exhaust manifold.

Ford Escort exhaust manifold.

Exhaust leak symptoms may include one or more of the following:

  • Rich fuel mixture
  • Poor fuel economy
  • Clicking, puffing or ticking noises
  • Poor acceleration
  • Faulty EGR system operation
  • Loud exhaust
  • Strong odor in the cabin
  • Smoke under the hood
  • Trouble Code P0420 or P0430 (Catalyst system efficiency below threshold)

The exhaust manifold collects high-temperature combustion gases and directs them through the downpipe, catalytic converter, muffler and tailpipe at the rear of the vehicle.

A leak may happen anywhere along the exhaust system. A cracked manifold, blown manifold gasket (used on some engines), a bad pipe gasket, or a rusted pipe may all allow exhaust gasses to escape and produce loud noises.

The following sections will help you find a potential exhaust leak. During this diagnosis, it's a good idea to have the vehicle repair manual for your particular vehicle make and model.

If you don't have this manual yet, you can find a relatively inexpensive copy through Amazon. Haynes manuals include images, pictures and step-by-step procedures for many troubleshooting, parts replacement and maintenance projects. So you can recoup your small investment in a short period of time.

And, in case your are wondering, in the following video you can hear the 'bubbly' sound coming from an exhaust leak.

Index

1. What May Cause an Exhaust to Leak?

2. Inspecting the Exhaust System

A simple method to find an exhaust leak

3. Removing the Exhaust Manifold

Leaking Exhaust Manifold Gasket Symptoms

4. Replacing an Exhaust Manifold Gasket

5. Diagnosing an Exhaust Pipe or Joint Leak

Video: Leaking Exhaust Joint Donut

6. Preventing Expensive Exhaust System Repairs

exhaust-leak-diagnosis

1. What May Cause an Exhaust to Leak?

There could be several reasons why and exhaust system may start to leak. Some of the most common reasons are:

  • Rust, caused by water (a byproduct of the combustion process), road salt, or snow.
  • Thermal stress from the constant heating and cooling cycle.
  • Road damage.
exhaust-leak-diagnosis

2. Inspecting the Exhaust System

Before you begin troubleshooting the exhaust system in your car, if at all possible, try to find out in what area of the system the potential leak is located.

This may seem obvious but you can save a lot of time just by taking note of some of the evidence at hand.

Where to start looking:

1. Does a ticking, puffing or loud noise under the hood seems to stop after the engine warms up?

Start your diagnostic at the exhaust manifold, including the gasket area.

2. Can you smell exhaust fumes from inside the cabin any time you are driving?

You may be dealing with a leaking manifold, a leak in the downpipe between the manifold, catalytic converter or one of the joints.

3. Is there a loud, rhythmic noise coming from under the vehicle any time you start the engine?

Check for a leak along the exhaust pipes and joints.

4. Can you see smoke coming from under the vehicle when you start the engine?

Start the engine and take a look under the vehicle to see which part of the exhaust the smoke seems to be coming from.

5. Is the exhaust system too loud?

Check for a hole, rusted or black soot area in the downpipe, joint, catalytic converter or muffler. However, when inspecting the muffler, you may find a small hole at the back of it. That's a water drain hole to prevent rust buildup. So don't worry about that.

A simple method to find an exhaust leak:

A popular technique to locate exhaust leaks is to connect a vacuum cleaner to the tailpipe of your car. The vacuum cleaner should be able to blow air.

When the engine has cooled, connect the vacuum cleaner to the tailpipe of your car, turn on the vacuum cleaner, and start spraying soapy water around the exhaust manifold, downpipe, catalytic converter, muffler and joints.

Bubbles will form around the leaking spot.

Once you've found the leak, decide whether it's something you are able or want to fix yourself. There are several repair methods to deal with exhaust leaks.

A quick internet search can turn several videos and articles suggesting how to fix exhaust leaks.

Just keep in mind that using aftermarket products to deal with manifold cracks or broken pipes too close to a catalytic converter or muffler may not work too well because of heat expansion. Welding a crack or replacing a catalytic converter or muffler may be the best option in some cases.

exhaust-leak-diagnosis

3. Removing the Exhaust Manifold

You've discovered a leaking exhaust manifold or gasket. Sometimes, an exhaust manifold repair can be done in place. For example, if the damaged area is accessible, you may weld a crack without removing the manifold; other times, it may be necessary to remove the manifold for a closer examination, for repairs, or to replace a blown gasket.

These steps will help you remove the exhaust manifold:

  1. Before removing mounting bolts or nuts, apply a quality, penetrating oil like Aero Kroil to mounting hardware. Kroil is a good, commercial grade product. It works great on difficult to remove rusted bolts.
  2. Let the oil penetrate for a couple of hours each time. Follow the instructions that come with your product. This will help you remove and prevent damage to exhaust bolts.
  3. Make sure the engine is cool and disconnect the battery.
  4. Set the transmission to Park (automatic) or Neutral (manual).
  5. Engage the emergency brakes.
  6. You may need to raise the front of your vehicle to gain access to mounting bolts under the manifold. Safely support the vehicle on jack stands.
  7. When loosening mounting hardware, check for loosen or broken bolts, nuts or studs. This may indicate the source of a leak.
  8. Loosen mounting bolts and nuts gradually, starting at the center of the manifold and work your way outward, alternating left and right-hand side bolts. Do this in three steps or more, loosening all the bolts a bit once, than do a second pass, and so on until you've removed all the mounting hardware.
  9. Once you've removed all the mounting hardware, you may need to rock the manifold up and down to free it from the cylinder head. Don't use a screwdriver or similar prying tool to dislodge the manifold. You may damage the mating surfaces and cause a very expensive repair.

If you are not sure whether it's necessary to remove the manifold for repairs, consult with your car shop. You may save time and money.

exhaust-leak-diagnosis

Examine the Exhaust Manifold

After removing the manifold, thoroughly examine the body for cracks or damage.

  • Look for buildup or corrosion around the mating surfaces on the cylinder head and manifold. Corroded or carbon filled spots may indicate a leaking area.
  • If your manifold comes with a gasket, look for spots covered with soot that may indicate a leak.
  • Whether the old gasket is the source of a leak or not, install a new gasket when reinstalling the exhaust manifold. Follow the instructions in your vehicle repair manual.
  • If you plan to reinstall the same exhaust manifold, take it first to a machine shop. When removed, a manifold may warp even slightly due to the thermal stress it is subjected throughout its service life.
  • If your manifold has dowel holes, make sure to thoroughly remove buildup inside. Dowel holes allow the manifold to expand during operation; otherwise, it may crack.
exhaust-leak-diagnosis

Reinstalling the Exhaust Manifold

The following suggestions can help you reinstall the exhaust manifold.

  • Install mounting hardware finger tight. Consult your repair manual for the tightening sequence and steps.
  • Tighten bolts and nuts gradually, in three or more steps, starting at the center and working your way outwards, alternating the left and right-hand side bolts.
  • Finally, torque the bolts to specifications. Your vehicle repair manual list the correct torque for your exhaust manifold, but you may also find the torque listed online.

Following a proper installation sequence will prevent damage to mounting hardware, gasket and exhaust manifold.

exhaust-leak-diagnosis

4. Replacing an Exhaust Manifold Gasket

If you need to replace the exhaust manifold gasket, follow the suggestions in the previous section Removing the Exhaust Manifold. Then, proceed with the following steps.

  1. Use a plastic scraper to remove traces of old gasket material from the mating surfaces on the exhaust manifold and cylinder head.
  2. Soak a rag in lacquer thinner or acetone and clean the mating surfaces.
  3. Have the exhaust manifold checked for warping, before installing a new gasket. Some manifolds may warp after being removed.
  4. Follow the manufacturer instructions to install the new gasket.
  5. Make sure that both mating surfaces are completely clean to prevent future leaks.
exhaust-leak-diagnosis

5. Diagnosing an Exhaust Pipe or Joint Leak

Making a visual inspection of exhaust system pipes and components.

  1. Set the transmission to Park (automatic) or Neutral (manual).
  2. Raise the front or rear of the vehicle, as necessary, and safely support it on jack stands.
  3. Chock the front/rear wheels.
  4. Put on your goggles, protective gloves and, with a flashlight in hand, get under the vehicle.
  5. Inspect along the exhaust pipes and joints, starting at the manifold, working your way down to the muffler and tailpipe.
  6. Pay special attention to rusted or soot-black spots. You may need a telescoping mirror to check on hard to reach areas.
  7. If necessary, ask an assistant to start the engine and let it idle.
  8. Then ask your assistant to cover with a shop rag the opening at the tailpipe. This may help force exhaust gasses through hard to find leaking spots along the pipes and joints. Also, pay special attention to loud noises coming from a pipe or joint.
  9. If necessary, ask your assistant to step momentarily on the gas pedal to increase exhaust pressure in the system while you watch pipes and joints for leaks.
  10. Pay close attention to joints where the downpipe connects to the manifold, catalytic converter and muffler, depending on your particular model. Donut gaskets at these spots are candidates for leaks because of vibration that cause bolts to loosen or break. Usually, you can fix leaky joints by replacing a gasket or bolts.

The next video shows you how a missing joint donut was causing a loud noise in the exhaust.

Leaking Exhaust Joint Donut

exhaust-leak-diagnosis

6. Preventing Expensive Exhaust System Repairs

A leaking exhaust system can be dangerous, not only for your vehicle but for yourself and any other person riding with you. Highly poisonous exhaust gasses may leak into the cabin.

Diagnose your exhaust system as soon as you suspect a problem with it, and make the necessary repairs.

Sometimes, locating the source of a leak is not easy. Car shops use compressed air and smoke machines to diagnose exhaust system leaks.

However, car technicians frequently use visual inspection as well, just like the way you can do at home. That's because, in many cases, it's possible to locate leaks just by examining the manifold, joints, and pipes, if you know how and what to look for.

The steps outlined in this post will help you locate even difficult to find exhaust leaks.

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2021 Dan Ferrell

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