Find out why your car sounds like a lawn mower

This article will explain what causes your car to sound like a lawnmower and what you can do to fix it.

If your car sounds like a lawn mower when you hit the gas pedal, you are probably dealing with an exhaust system leak. The gas fumes produced inside the engine leak out of the exhaust system before reaching the catalytic converter and, ultimately, the tailpipe.

Car exhaust pipe expelling smoke

How does the exhaust system work?

A car’s exhaust system is responsible for controlling the noise and directing the gases away from the passengers to the car’s back. The exhaust system is comprised of:

  1. Exhaust manifold – this is where the gases produced in the engine chamber go through first.
  2. Pipes – they are required for directing the gases at the back of the car.
  3. Catalytic converter – is responsible for converting the harmful emissions into less harmful gases, making your car more environmental friendly.
  4. Muffler – the role of the muffler is to reduce noise by redirecting the airflow.
  5. Resonator – is an optional device, which helps reducing the noise even more.

What are the symptoms of an exhaust leak?

As you might have noticed already, one of the first signs that you have an exhaust leak is a change in how your car sounds, especially when accelerating.

Loud engine noise

People compare the loud rattling noise to the sound of a lawn mower or a motorboat. The sound gets more noticeable when accelerating the car.

Fumes inside the cabin

Apart from the loud rattling noise, you might smell gas fumes while driving. A damaged pipe from the exhaust system can allow fumes to get into the cabin.

Poor fuel economy

An exhaust leak might cause your mpg to drop. The engine might run less efficiently due to an imbalance in the air-to-fuel ratio.

Worse engine performance

The engine can lose power as a result of a leak in the exhaust system.

Where are most exhaust leaks located?

Exhaust system leaks usually happen in the system’s manifold or other joints of the system. If the car is older than five years, gaskets can start to wear out and rust can form on the connections between exhaust system components.

Short journeys will facilitate the formation of exhaust leaks, as the exhaust system does not get hot enough to vaporize the water generated during combustion.

Can you drive with an exhaust leak?

Driving with a faulty exhaust system is both illegal and dangerous. As discussed already, a leak in the exhaust can allow gas fumes to get into the cabin, leading to monoxide poisoning.

If the leak is situated next to wires, the hot fumes produced by the engine can melt the wire insulation, resulting in a short circuit.

While one may think an exhaust leak is not dangerous, it can definitely be.

What does exhaust leak smell like?

If your car has an exhaust system leak behind the catalytic converter, you might notice a strong gas smell inside the car cabin. If you open the bonnet, you might also notice a burning smell coming from the engine bay.

Are exhaust leaks easy to fix?

Exhaust leaks can be difficult to fix on your own, as some leaks require welding. I recommend taking the car or truck to a mechanic for a proper inspection of the car. He will have the tools to repair your exhaust.

However, if you want to take the matter into your own hands, here is what you should do.

  1. Jack up your vehicle so you can have access underneath
  2. You can spray soapy water on the exhaust and pay attention to any forming bubbles.
  3. Assessing the type of damage will let you know if you can do the repair yourself or need a professional.
  4. If you notice a small crack or hole, you could use exhaust tape to fix it.
  5. If there is an entire component that needs replacing, you might need to get the car to a mechanic.

How much does it cost to fix an exhaust leak?

The price of fixing an exhaust can range quite a lot, from $50 for welding a small crack to over $1000 for a new catalytic converter. However, most of the time, fixing a leaking exhaust system will not break the bank as long as the problem is identified early enough.

Will an exhaust leak throw a code?

Most of the time, an exhaust leak will not throw any code. However, as the problem gets worse, the oxygen levels in the exhaust system might drop, resulting in error codes. However, it can cause your car to burn more fuel, for example. This will alert you that the car is not running as usual.

Can a exhaust leak cause a misfire?

I have definitely had cars that had cylinder misfires as a result of an exhaust manifold leak. As oxygen levels rise in the exhaust, the oxygen sensor will falsely communicate to the PCM to increase the amount of fuel delivered to that bank of cylinders. The extra fuel will result in added carbon on the plugs and eventually misfires.

Will an exhaust leak cause the check engine light to come on?

As mentioned already, an increase in oxygen levels will result in a false lean condition reading. As a result, the ECU will compensate by adding more fuel to the mixture.

This will cause the Check Engine Light to come on. However, a small exhaust leak is less likely to cause your Check Engine Light to light up.

Final thoughts

Some car problems can be prevented if you take good care of your car or truck. If your vehicle is older than 7 years, I recommend that you ask the mechanic for an exhaust inspection whenever you have your car in the garage for its service.

Small leaks or minor damage can be identified and repaired before getting more costly to repair. If you drive your car with an exhaust leak for too long, you risk damaging other car components.


Why Exhaust Systems Wear Out

How an Exhaust Leak Affects Wideband/O2 Sensor Readings