How And Why A Catalytic Converter Affects Your Gas Mileage

A catalytic converter is a stationary device in your vehicle’s exhaust system. But can a catalytic converter affect gas mileage? 

I am an ASE certified auto mechanic with a degree in Applied Science. I have well over 20 course hours on engine drivability issues and emission control systems was one of them. In those classes we learn in detail the functionality of catalytic converters. 

As well, I work on various types of vehicles with catalytic converters and test them using the latest tools regularly.

What Is A Catalytic Converter?

A catalytic converter is a device that takes the exhaust gasses from your vehicle and converts them from pollutant ones to non-pollutant ones. The device is installed in your vehicle’s exhaust system and the exhaust gasses run over precious metals inside the catalytic converter. 

These precious metals usually consist of platinum or palladium. When exhaust gasses pass through the converter, they interact with the precious metals, called a catalyst, chemically altering the harmful exhaust gasses into less pollutant ones. 

For example, a catalytic converter can turn carbon dioxide into water. The main purpose of the catalytic converter is to reduce the amount of pollution that’s released into the air. 

The catalytic converter is a crucial part to a vehicle’s emissions control systems and is even legally mandatory in lots of countries in order to curb pollution caused by vehicles. 

Catalytic converters were invented by a chemical engineer named Eugene Houdry in response to high pollution levels in Los Angeles, California. 

It wasn’t until the 1970’s that catalytic converters started to be installed on all different makes and models of vehicles. 

What Can Affect Fuel Economy?

A number of factors can affect your vehicle’s fuel economy including vehicle engine size, driving habits, and vehicle weight. 

Engine size can affect your vehicle’s fuel economy. Larger engines wield more power therefore, they need more fuel to operate at efficient levels. For example a V8 engine will require 4 more cylinders having gas injected into them than an inline 4 engine, therefore V8’s need more fuel. 

Heavier vehicles require more energy to move, meaning they will be requiring more fuel to operate. Another important factor that plays into fuel economy is your driving habits. Fast and aggressive driving will cause your vehicle to use more gas than even steady driving. 

Constant, hard braking will cause the engine to stop and start quickly causing your vehicle to use more fuel as well. Tire pressure can affect fuel economy too. Underinflated tires will cause your vehicle to work hard and use more fuel. 

Aerodynamics play a crucial role in your vehicle’s fuel efficiency. Vehicle’s with boxier shapes tend to get less mileage per gallon than cars with more aerodynamically shaped vehicles. 

Vehicles that have regularly scheduled maintenance performed such as replacing air filters or having tune ups done will get better gas mileage than vehicles that ignore maintenance items as such. 

The type of fuel your vehicle uses can have a different effect on gas mileage too. For example, gasoline typically has a higher energy density than diesel, which can result in better gas mileage for gasoline-powered vehicles. 

Finally, road conditions can also affect gas mileage. Hilly and windy roads will cause your vehicle to have lower gas mileage than straight and level roads. 

As you can see, a number of factors can play a role in your vehicle’s fuel economy. So if you’re wondering why you’re not seeing numbers like you’re used to, check these circumstances first before diving into potential issues with your vehicle. 

How Can A Catalytic Converter Affect Fuel Economy?

A healthy catalytic converter will have no effect on a vehicle’s fuel efficiency, but a bad catalytic converter can cause around 1-2 psi of back pressure in the vehicle’s exhaust system. 

This extra back pressure caused by a bad catalytic converter will cause your engine to work harder, therefore decreasing fuel efficiency. So a healthy catalytic converter causes almost no extra back pressure, therefore having no effect on fuel efficiency. 

The amount of fuel lost due to a clogged up converter can range from a 5-10% decrease in fuel efficiency. Catalytic converters can also burn unburnt fuel that passes through the exhaust system. This technically increases fuel efficiency while also saving the environment from having unburnt fuel released into the atmosphere. 

On the other hand, enough unburnt fuel on the catalytic converter can cause serious damage to the catalytic converter. A catalytic converter can reach up to 1000 degrees, and that’s just to reach operating temperature. 

If you add unburnt fuel to the converter, it risks the chance of adding heat to the converter and melting the catalyst materials inside the converter. 

If you suspect fuel is leaking out of your exhaust, fix the issue immediately. Some signs of unburnt fuel reaching your exhaust are a strong smell of fuel coming from your tail pipe or black smoke coming from your tailpipe. 

Signs Of A Failing Catalytic Converter

A catalytic converter can fail for a number of reasons. In this section, let’s review some common signs and symptoms of catalytic converter failure. 

• Poor engine performance: A bad catalytic converter can cause poor engine performance since the exhaust flow is restricted. This restriction in the exhaust system can cause the engine to run poorly or to run, making it feel like there’s no power coming when you press down your gas pedal and go wide-open-throttle. 
• Increased fuel consumption: A bad catalytic converter can cause increased fuel consumption because it causes the engine to work harder in order to overcome the pressure built up in the exhaust system. This extra pressure the engine has to overcome will cause the engine to use more fuel, therefore, increasing fuel consumption. 
• Check Engine Light: Your check engine light may come on due to a failing catalytic converter. This is because there are sensors that monitor the effectiveness of your converter and if they recognize your converter is working below a certain threshold due to ineffectiveness, the vehicle’s computer will put a check engine light on your vehicle’s dashboard. 
• Bad acceleration: If your catalytic converter is clogged or has lost effectiveness, it can cause the engine to struggle and result in reduced acceleration.
• Excessive exhaust smoke: A failing catalytic converter may cause an increase in exhaust smoke,  which can be visible as a black or gray cloud coming from the tailpipe.
• Rattling or vibrations: A damaged catalytic converter can cause rattling or vibrations, which may be audible or felt through the floorboards of the vehicle.

If your catalytic converter does fail, make sure to replace it, since cleaning it does nothing in terms of restoration. Catalytic converters can be a huge pain to replace, so if you’re not comfortable doing the job yourself, make sure to take it to a certified technician to get the job done.

Key Takeaways 

• A catalytic converter converts harmful exhaust gasses into non-pollutant ones. 
• There are many factors that can affect fuel economy.
• Only a bad catalytic converter can affect fuel economy. 
• A clogged up converter can cause a 5-10% decrease in fuel efficiency.
• A bad catalytic converter can cause 1-2psi of backpressure inside the exhaust system.