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Fact or Fiction: Can Catalytic Converters Catch Fire?

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In 2018, approximately 90,000 acres of the Sierra National Forest near the Yosemite were burned to the ground. The Ferguson fire burned for over a month before it was fully contained, injuring roughly 19 people and causing the death of two firefighters in its wake. Investigations later discovered the cause of the deadly fire—a “superheated” catalytic converter.

Vehicles catching fire or causing fires are not uncommon, and every now and then, a bad catalytic converter (or “cat,” for short) will be involved in an incident. There are various reasons for catalytic converters to fail to work properly, including manufacturing defects. In this year alone, more than 500,000 Hyundai and Kia vehicles were recalled because of faulty cats. While many people are aware that a catalytic converter can be a safety hazard when in bad condition, only a few understand exactly how it can become a fire risk.

In the 1970s, stricter emissions standards—enforced by the Environmental Protection Agency (EPA) through the Clean Air Act—prompted car manufacturers to develop a range of technologies that would help build “cleaner” vehicles.

How does a catalytic converter work?

Air pollutants have been a concern in major cities as early as the 1940s. Smog and low-level ozone resulting from noxious gases produced in the combustion process had long been identified as leading causes of diminished air quality.

In the ’70s, stricter emissions standards—enforced by the Environmental Protection Agency (EPA) through the Clean Air Act—prompted car manufacturers to develop a range of technologies that would help build “cleaner” vehicles. The modern catalytic converter, which essentially makes the combustion process cleaner, is considered one of the greatest environmental inventions of its time.

So what does a catalytic converter do?

The catalytic converter is a vital component of your vehicle’s exhaust system, which is made up of one or more exhaust pipes that run the length of your vehicle’s undercarriage. Together, all your exhaust components work to transport toxic gases that are produced during combustion away from the engine, and process them so they can be safely released into the atmosphere.

Gases go through the catalytic converter before they are released through the tailpipe. This component burns off the harmful pollutants from exhaust gases with the help of catalysts. In this way, the catalytic converter is crucial in minimizing the impact of vehicle emissions on air pollution.

Can the catalytic converter catch fire?

The short answer is no. The catalytic converter itself won’t burst into flames, but it can become a fire hazard. An overheated catalytic converter can ignite surrounding flammable materials while it’s running hot.

Under normal circumstances, catalytic converters operate within a temperature range of 1,200 to 1,600 degrees Fahrenheit. An overworked or clogged catalytic converter, on the other hand, can reach temperatures above 2,000 degrees Fahrenheit.

The trouble starts when hot parts of the catalytic converter break off from the car or pieces of exhaust carbon shoot out of the tailpipe. These could ignite a patch of dried grass or a pile of dried leaves. In theory, these can even ignite your car’s cabin insulation and carpeting through the heat shields and floor pan. At the same time, extremely high temperatures may cause long-term damage to the exhaust system’s surrounding parts.

The catalytic converter itself won’t burst into flames, but can ignite surrounding flammable materials when overheated.

What causes a catalytic converter to overheat?

There are several reasons why your vehicle’s catalytic converter may overheat. Here are some common causes you should look out for.

1. Worn-Out Spark Plugs

One of the most common causes of an overheated catalytic converter is an engine that isn’t working properly, which can be a result of worn-out spark plugs. Damage on the wire or tip of the spark plug can cause the engine to misfire, leading to a spike in exhaust emissions.

If the engine is not burning fuel efficiently, the exhaust system may get overwhelmed. In the process, the cat will need to work harder to burn off more exhaust pollutants than it was designed to handle.

2. Excess Antifreeze Entering the Exhaust

Excess antifreeze entering the exhaust system can create a heavy buildup of carbon deposits in the catalytic converter. Carbon soot may coat the catalyst, making it unable to convert harmful emissions.

Carbon deposits can also clog emissions flow and increase backpressure in the system. If this happens, burnt exhaust gases can be drawn back into the combustion chamber, resulting in reduced efficiency and overheating in the engine compartment.

Excess antifreeze entering the exhaust system can create a heavy buildup of carbon deposits in the catalytic converter.

3. Malfunctioning Oxygen Sensor

The oxygen sensor is a component that measures the engine’s air-to-fuel ratio. Incorrect readings due to sensor failure can cause the engine to run rich. When too much fuel is delivered to the engine, raw fuel is likely to be pushed into the exhaust system. If this happens, internal temperatures can rise to a point where the honeycomb mesh inside the converter and substrate are destroyed.

4. Damage from Road Debris

The catalytic converter can get cracked or punctured by impact from road debris or by running over a curb because it’s located underneath the vehicle. A leak in this component may result in an increase of backpressure in the system, causing it to overheat.

How to Prevent Fires Involving Overheated Catalytic Converters

Catalytic converters do not have moving parts, which means overheating is more likely to be caused by factors outside the component itself, such as engine system failure or fuel contamination. Therefore, the best way to prevent a failing catalytic converter is to be diligent about following your vehicle’s maintenance schedule.

Here are other ways to keep your catalytic converter from overheating and becoming a fire hazard:

1. Watch out for symptoms of a bad catalytic converter.

Repair and replacement of a catalytic converter must only be done by a licensed mechanic. While it’s not advisable to work on this part on your own, there are several signs that can help you determine when you should have it checked by a professional.

Reduced Engine Performance

A clogged or damaged catalytic converter will make it harder for your vehicle to accelerate. Burning more gas than usual for the same amount of power during acceleration can be a sign that there’s a problem with your catalytic converter.

Rattling Noises

Noises that sound like rocks hitting the underside of your vehicle are another sign you should look out for. Abnormally high temperatures can damage the internal mesh of the catalytic converter, which can produce rattling noises.

Noises that sound like rocks hitting the underside of your vehicle are another sign you should look out for.

Sulfur Smell from the Exhaust

A rotten egg-like smell may exude from the exhaust system if the sulfur in gasoline is not properly converted into odorless sulfur dioxide. You may also observe dark smoke released from the exhaust along with this odor.

2. Check for applicable vehicle recalls.

Recently, there have been multiple recalls for vehicles that have faulty catalytic converters and engine components that may compromise the exhaust system. You may check the National Highway Traffic Safety Administration (NHTSA) website for information on recalls applicable to your vehicle.

For instance, the 2017-2018 Chrysler Pacifica Plug-in Hybrid was recalled due to a failure of the gas engine to restart properly after running on PHEV propulsion mode. This issue could cause unburned fuel to enter the exhaust system and melt the catalyst.

2012-2016 Kia Soul SUVs equipped with the 1.6L Gasoline Direct Injection (GDI) engines were also recalled due to the possibility of overheating catalytic converters. Unusually high exhaust gas temperatures have been observed in the catalytic converter, allowing substrate particles to enter the combustion chamber.

Extreme temperatures in the catalytic converter can result in abnormal engine combustion, which may lead to one or more of the engine’s pistons to break and possibly puncture the engine block. Engine oil is highly flammable and may ignite a fire if it comes in contact with a hot exhaust surface.

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CarParts.com

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In the Garage with CarParts.com is an online blog dedicated to bringing DIYers and devoted car enthusiasts up to date with topical automotive news and lifestyle content. Our writers live and breathe automotive, taking the guess work out of car repairs with how-to content that helps owners get back on the road and keep driving.

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