A catalytic converter (or cat) is an emissions device that looks like a small muffler connected to the exhaust system. If you were to pull your modern vehicle onto a mechanic’s lift and look up, you would see the bottom of your vehicle and most likely the entire exhaust system.
From the engine, you would find the exhaust manifold carrying hot spent exhaust gases away from the engine. In modern vehicles, the first catalytic converter might be integrated into the exhaust manifold, followed by another cat later on.
An older vehicle might have only one catalytic converter located after the manifold but well before the resonator, muffler and exhaust tips. Inside the catalytic converter are a number of precious metals, such as platinum, palladium and rhodium.
What do catalytic converters do?
A catalytic converter changes dangerous and polluting exhaust gases into less dangerous forms. A “catalyst” is a substance that causes a chemical reaction but is not changed or consumed during that reaction, while a “converter” is a person or thing that converts something.
Smooshing those together gets us the explanation that catalytic converters function by an internal substance that chemically changes exhaust gases into something else.
Here’s how that works.
Exhaust gases exiting the engine are hot, up to 1,200 degrees Fahrenheit, and contain hydrocarbons, carbon monoxide and nitrogen oxides. Those first two combine to form ozone, what we commonly see as smog.
As the hot gases enter the catalytic converter, they encounter a combination of precious metals. These metals are the catalyst, spread out inside the converter on a honeycomb-looking structure. This design allows maximum coverage of the passing exhaust gases with minimum flow restrictions, meaning the catalysts can convert the gases to less toxic forms without slowing down the flow. Testing shows catalytic converters are more than 90% efficient at converting polluting gases into less harmful carbon dioxide, nitrogen and water vapour.
What does a catalytic converter do to car performance?
Unfortunately, the claim that cutting off the catalytic converter will improve gas mileage is a debate that isn’t backed by the science of how cars function. The oxygen sensor, which is located in the exhaust pipe, tries to correct for the weird readings it sees when the cat isn’t present. As a result, your car will increase fuel intake to compensate.
How long does a catalytic converter last?
In many cases, the catalytic converter will last as long as you own the vehicle. While catalytic converter theft is on the rise, a catalytic converter in normal conditions should last around 10 years. Keep this in mind if you regularly buy used cars. The average age of used cars on the road is more than 12 years, so the catalytic converters on these older cars might be suspect or nearing the end of their functional life.
Signs you may need a new catalytic converter
If, after reading all this bad news, you wonder if you need a new catalytic converter, look at the most common symptoms of a failing catalytic converter. If your vehicle runs fine, odds are you are good to go, but here’s what to look out for.
Check engine light: If your check engine light is on, you can often have the light diagnosed at a fee. One of the failures it might reveal is a broken catalytic converter. When the converter fails, the exhaust flow rate and temperature are out of normal operating limits, sending up that dreaded check engine light.
Sulphur Smell: Hydrogen sulphide is a naturally-occurring compound in petroleum products and can cause a big stink in gasoline. When a catalytic converter fails, it is unable to break apart this (or any other) compound.
Hydrogen sulphide can be smelled even in low concentrations, which is why a broken catalytic converter is often associated with a rotten egg smell.
Rattling noise from under the vehicle: If the internal (and expensive) catalyst structure breaks apart, the honeycomb structure can sound like random chunks bouncing around inside the converter housing as you drive. The rattling might be more noticeable on startup and will likely get worse over time as the cat breaks down into smaller pieces.
Poor engine performance:
Think about how an engine exhaust system works for a moment. The engineers designed the exhaust system so the spent gases could be quickly swept away through a functioning exhaust system. If a catalytic converter fails internally and blocks the rest of the exhaust system with broken pieces, the exhaust flow will be severely reduced from backpressure. This results in sluggish engine performance.
Decreased fuel mileage: Say you were averaging 550km a tank before, but now you’re struggling to reach 400. This dramatic decrease in fuel mileage is common when a catalytic converter fails because the exhaust can’t easily clear the blockage, the next intake cycle doesn’t bring in as much fresh air as the engine needs. The result is too much fuel used for not enough movement—and more frequent stops at the pump.
Nelson Xavier Ssenyange
Team Leader
Germax Auto Spares & Garage
Lukade Road, Naalya
0779250886/0752088734