What are the signs of a faulty exhaust manifold?

Car exhaust manifold

The exhaust manifold is crucial in ensuring your vehicle performs well and is safe to drive. If your vehicle’s check engine light comes on or you hear unusual noises from the engine, it could be a sign that your exhaust manifold has a problem. 

We’ll explore what this critical engine component does, how to spot problems, and what causes those problems. Identifying and fixing issues with the exhaust manifold can help you keep your car running safely, smoothly and efficiently.

Table of contents:

What does the exhaust manifold do?

The exhaust manifold is an essential part of your car’s exhaust system. It directs the engine’s exhaust gases to the catalytic converter. V-shaped engines have two manifolds on each cylinder bank, while inline engines have one central manifold. These parts deal with harsh conditions, like extreme heat, so they need regular check-ups and maintenance

It’s essential to watch for any exhaust leaks or worn-out parts. Leaks can let unhealthy fumes into the cabin, which isn’t good news for you or your passengers. They can also make your engine feel sluggish. With routine exhaust care and replacing damaged pieces when needed, your car can keep running smoothly and keep you safe from dangerous gases.

What are the symptoms of a faulty exhaust manifold?

Unusual noises 

Listen out for tapping, hissing or rattling sounds from the engine. These may be more noticeable in cold startups. As the manifold cracks and leaks, the exhaust sounds louder and rougher. 

Have any new sounds inspected by a mechanic, even if they disappear after the engine warms up.


The smell of burning exhaust fumes in the cabin is a telltale warning sign of an exhaust manifold leak. Toxic gases containing carbon monoxide and carbon dioxide can enter the vehicle through cracks or holes.

However, be aware that the exhaust manifold can also leak odourless gases into your car, so other signs are important to look out for, as well as unusual smells

Rusty exhaust manifold

Cracks or rust

Exhaust manifold cracks and holes will cause exhaust gases to leak before they reach the catalytic converter. Carefully inspect the manifold for signs of exterior cracks, rust, or carbon buildup. 

The manifold will continue to crack or rust. Don’t delay diagnosis and repair, as a growing manifold leak can lead to engine damage if left unchecked. Addressing it early gives the best odds of an easy and inexpensive fix.

Performance issues

An exhaust manifold leak can significantly impact your vehicle’s performance and accelerate wear on other components. 

At first, a small leak may only cause a minor loss of power during acceleration. However, over time, the issue will worsen. You’ll notice increasingly sluggish acceleration and lack of responsiveness as more exhaust gases escape through cracks or holes before reaching the catalytic converter.

Check engine light

An illuminated check engine light often indicates an exhaust manifold leak. Your vehicle’s diagnostic sensors will detect incorrect oxygen levels and emissions caused by gases escaping before they reach the catalytic converter. Have the codes read to confirm the source.

Failed emissions

If there’s a problem with your vehicle’s exhaust manifold, it’s doubtful it will pass an emissions test.

Emissions monitoring equipment will detect the high CO levels and hydrocarbon readings as unburned gases escape through cracks before reaching the converter. This makes passing MOT inspection difficult until the exhaust manifold is repaired. 

Overheating engine

Possible causes of an exhaust manifold leak

Here are some of the most common causes of an exhaust manifold leak:

  • Cracks: The constant heating and cooling cycles and engine vibration can cause small cracks and holes in the manifold. These will worsen as exhaust gases escape through the openings.
  • Rust and corrosion: Moisture and road salts can cause rust on the manifold’s surface. On older vehicles, severe rusting can eat through the metal – causing leaks.
  • Loose bolts: The bolts and gasket that connect the manifold to the engine head can become loose over years of vibration. This allows exhaust to slip out of the seal.
  • Warping: Excessive heat will eventually warp the manifold, distorting its shape and compromising or breaking the gas seal. 
  • Physical damage: Impact from debris on the road or minor collisions can dent, twist, or crack the manifold. This kind of damage usually causes immediate leaks.
  • Carbon buildup: Carbon deposits inside the manifold can gradually block or restrict exhaust flow, forcing gases past gaskets and seals.
  • Engine overheating: An overheated engine stresses exhaust components like the manifold.

What to do if you think you have a faulty exhaust manifold

Before replacing the exhaust manifold, rule out a damaged gasket as the culprit. Gaskets can produce similar symptoms but are a cheaper fix. However, dealerships will usually recommend you replace the entire manifold, regardless of the extent of the damage. This can end up being pricey. 

Instead, visit a trusted mechanic or exhaust specialist.  With welding or brazing, a skilled exhaust pro can often patch small manifold cracks at a fraction of the replacement cost. The repair may not last as long as a whole new manifold but makes sense budget-wise in less severe cases. 

Replacement is the best long-term solution for significant cracks or irreparable damage, either with a new or used exhaust manifold. Either way, have an exhaust specialist accurately diagnose the problem’s extent first. Only let a dealer convince you the only option is an expensive replacement manifold after thoroughly assessing the size of the damage first. 

How to check for a leak in the exhaust manifold

Regular inspection and swift repair of leaks are key to avoiding worsening manifold damage. If you’re unsure, just ask a trusted mechanic to do it for you; otherwise, follow these steps to do it yourself:

  • Do a cold engine start and listen for tapping or ticking noises that signal a manifold leak. Identify the source.
  • Inspect the manifold for signs like soot marks, missing bolts, or rust or cracks that suggest an exhaust leak. You may need to remove it to check for hairline cracks.
  • Wash the manifold, then place a spirit level across its surface. Shine a torch from beneath – light glowing through indicates it’s warped.
Removing old exhaust manifold gasket

What happens if I don’t get my exhaust manifold fixed? 

Firstly, your car’s engine performance will suffer. It will feel less responsive and less powerful, and fuel consumption will increase, costing you more money. It will also sound noisier and vibrate more, resulting in a more uncomfortable ride. 

More severe consequences can follow. Your vehicle is unlikely to pass an emissions test if the damage worsens. It could even lead to engine damage, driving up repair costs over time.

Finally, and most importantly, you could expose yourself and your passengers to exhaust gases that make their way into the vehicle’s cabin, including odourless and harmful carbon monoxide.

To avoid these issues, ensure you get any problems with your exhaust manifold checked out immediately. This ensures your vehicle maintains its performance, fuel efficiency, and safety.

This entry was posted in Maintenance on by Justin Smith.

About Justin Smith

As the man at the helm of BreakerLink, it is no surprise that its Director, Justin Smith, has always had a keen interest in cars, bikes and most things wheeled. Having spent over two decades in the car parts industry, Justin combines his passion that since 2002, has successfully united those looking for new and used car parts with the breaker that supplies them. Follow Justin on LinkedIn.

Disclaimer: These articles are for guidance purposes only. If you have any questions regarding any matter relating to your vehicle we would recommend that you seek the advice of an appropriate professional. We accept no responsibility or liability should you suffer financial or personal damages in relation to the advice stated on this website.