2017-2023 McLaren 720S Exhaust: Rattles, Cracks, and Replacement Guide

Symptoms of Failure

A failing exhaust muffler on a McLaren 720S can present several distinct symptoms. While some issues are common to all exhaust systems, others are more specific to this high-performance application.

1. Metallic Rattling or Clunking Noises

One of the most frequently reported issues is a metallic rattling sound, especially noticeable at idle or low RPMs. This is often caused by the internal baffles or sound-deadening material breaking loose or collapsing inside the muffler housing. As the engine vibrates, these loose pieces rattle against the inside of the muffler case, creating a sound often described as a 'pebble in a tin can'. One owner of a 2018 720S reported this issue at just 4,000 miles, with the dealer diagnosing it as collapsed baffles requiring a full muffler replacement.

2. Increased Exhaust Noise or Change in Tone

A sudden or gradual increase in the loudness of the exhaust is a clear sign of a problem. This could be due to a crack or hole in the muffler body, a failed gasket, or a compromised weld. On the 720S, owners have also reported a 'puttering' or ticking noise, which can be an early sign of a crack in the exhaust manifold, a separate but related component that can fail. Any leak allows exhaust gases to bypass the sound-dampening chambers, resulting in a louder and harsher sound.

3. Exhaust Fumes or Unusual Smells

If you notice the smell of exhaust fumes inside the car's cabin, it's a serious safety concern that needs immediate attention. This indicates a leak in the exhaust system somewhere ahead of the tailpipe, allowing harmful gases like carbon monoxide to enter the passenger compartment. While a muffler leak is typically at the rear, any significant crack or break in the system can cause this symptom.

4. Visible Damage or Corrosion

A physical inspection can often reveal the source of the problem. Look for cracks, holes, or significant rust on the muffler casing and connecting pipes. On a 720S, it's also critical to inspect the welds where the pipes enter the muffler and where the exhaust manifolds connect to the turbochargers. A common failure point on the 720S is cracking of the factory welds on the turbo manifolds 🎬 Watch: Detailed breakdown of a major turbo manifold failure and repair. due to extreme heat cycles. While not part of the muffler itself, a manifold leak produces similar symptoms and is a known issue on this platform.

Known Issues, TSBs, and Recalls

While the muffler itself has not been the subject of a specific recall, there are related issues and one major recall for the 2017-2023 McLaren 720S that buyers should be aware of.

Known Issue: Turbo Manifold Cracks

A widely documented problem on the 720S is the cracking of the turbocharger exhaust manifolds. The factory welds can fail, or the metal next to the weld can fracture due to repeated, extreme heat cycles. Symptoms include a ticking noise from the engine bay, the smell of exhaust, and an audible exhaust leak. This is not a muffler failure, but it is a common exhaust system problem on these cars that can be misdiagnosed. The repair involves removing the turbochargers to weld and reinforce the manifolds, or replacing them at a significant cost.

Known Issue: Internal Muffler Baffle Failure

As mentioned in forums, the internal baffles of the stock muffler can collapse or break loose, even on low-mileage cars. This leads to a distinct metallic rattle at idle. The typical dealer solution is a complete replacement of the muffler assembly.

Recall: NHTSA Campaign Number 20V231000 - Fuel Tank Corrosion

A significant recall was issued for 2016-2020 720S models concerning a fire risk. A foam pad located under the fuel tank could trap moisture, leading to corrosion of the tank and a potential fuel leak. While not directly involving the exhaust, a fuel leak in proximity to hot exhaust components presents a severe fire hazard. The remedy involves dealers removing the foam pad and inspecting the fuel tank for corrosion, replacing it if necessary. Buyers of a used 720S should verify that this recall service has been performed.

Buying a Used Exhaust Muffler

Given the high cost of a new OEM muffler from McLaren, a used unit can be a cost-effective option. However, careful inspection is crucial to avoid buying a part that is already failing.

What to Physically Inspect:

• Shake the Muffler: When the muffler is off the car, shake it vigorously. If you hear any rattling or clanking, the internal baffles have failed. Do not purchase it. A good muffler should be quiet when shaken.
• Check for Cracks and Welds: Carefully inspect the entire muffler body and all pipe connections for cracks, especially around the welds. Pay close attention to the inlet and outlet pipes. Black soot streaks around a seam or weld are a clear sign of a leak.
• Look for Corrosion: Check for heavy rust or corrosion, particularly on the seams and lower surfaces where moisture can collect. While stainless steel is resistant to rust, it can still corrode, especially in areas where road salt is used.
• Inspect Hangers and Mounts: Ensure all mounting brackets and hangers are intact, straight, and free of cracks. A bent hanger can cause improper alignment and stress on the rest of the exhaust system.
• Examine the Flex Pipe: If the system includes a flex pipe section, inspect the braided metal for any fraying, stretching, or black soot that indicates a leak.

Cost Comparison

Replacing the exhaust on a McLaren 720S is an expensive proposition. Aftermarket systems are extremely popular, not just for performance and sound, but because they can sometimes be a more logical choice than replacing a failed OEM unit.

Installation Difficulty: 3/5

Replacing the muffler on a 720S is a moderately difficult job best suited for an experienced DIY mechanic or a professional technician. The rear bumper, undertray, and heat shields must be removed to access the muffler. The components are large and can be difficult to maneuver without a vehicle lift. Broken studs or bolts on high-mileage or corroded cars can significantly increase the complexity of the job. The estimated time for a professional to complete the swap 🎬 See this step-by-step walkthrough of a 720S exhaust installation. is around 3-5 hours.

Frequently Asked Questions (FAQ)