Rick's Free Auto Repair Advice

Catalytic Converter — What is it?

Catalytic Converter — What is it?

First off, it’s a CATALYTIC converter, not a Cadillac converter. A catalytic converter is designed to convert pollutants from your engine into less harmless carbon dioxide and water through a catalytic reaction.

A catalytic converter is part of the exhaust/emissions system

A catalytic converter is part of the exhaust system. It’s usually mounted right after the exhaust manifold. The catalytic converter contains a ceramic honeycomb that’s coated you’ll find a ceramic honeycomb coated with a microscopic layer of precious metals like Platinum, Palladium, Rhodium, and Cerium, along with iron, and manganese, and nickel. The exact mix of metals depends on the engine and the current state of emissions laws.

The metals were chosen because they can store excess oxygen in the exhaust stream. Then they combine oxygen in the exhaust stream with unburned hydrocarbons to clean up the exhaust and reduce emissions. The precious metals also react with oxides of nitrogen and turn them into water and nitrogen.

It’s best to think of a catalytic converter like an incinerator whose job it is to burn off excess gasoline, oil, and coolant that gets into the exhaust. So it reduces emissions of hydrocarbons, oxides of nitrogen, and carbon monoxide.

How a catalytic converter works

The first generation of converters were referred to as two-way converters because they oxidized carbon monoxide, giving it an extra oxygen atom—2CO + O2 → 2CO2. And, it oxidized unburned hydrocarbons (gasoline and oil), turning them into carbon dioxide and water.

However, two-way converters couldn’t eliminate oxides of nitrogen, which is the main component in smog. Oxides of nitrogen are considered a greenhouse gas and it contributes to acid rain. In addition, it’s an ozone-depleting substance that’s 300 times more potent than carbon dioxide (according to Wiki). So carmakers switched to three-way catalytic converters starting in 1981 to reduce oxides of nitrogen emissions.

A three-way catalytic converter converts oxides of nitrogen to nitrogen and oxygen in addition to the two jobs performed by the previous two-way converters.

How long does a catalytic converter last

There are no wear parts inside a catalytic converter and their oxygen storing and pollution-reducing capabilities never wear out on their own. But they can be damaged by feeding them too much motor oil, gasoline, coolant, or silicone sealants.

A catalytic converter can last the life of the vehicle if you don’t abuse it. Catalytic converters don’t die on their own—they’re murdered. Here’s the bottom line: Catalytic converters do NOT wear out, they are killed by owner negligence. That’s right, YOU kill your catalytic converter by ignoring misfires, not fixing oil and coolant leaks, and by hitting things with the undercarriage.

What causes a Catalytic Converter to Fail?

An engine misfire is the number one cause of catalytic converter failure. When a cylinder misfires, it dumps raw fuel into the converter causing it to overheat as the converter tries to oxidize the excess fuel. If the misfire continues long enough, the converter can overheat to beyond 1,300 degrees, causing the ceramic honeycomb to meltdown. That plugs up the openings in the honeycomb restricting exhaust flow and reducing the engine’s ability to breathe. A meltdown can also cause the honeycomb “brick” to shatter, causing a catalytic converter rattle sound. A converter can also be damaged by impact or contamination from a leaking cylinder head gasket that sends coolant into the exhaust.

How much does a catalytic converter cost

The cost of a new catalytic converter depends on where you buy the unit. Carmakers are required to place a long warranty on their catalytic converters. In fact, the law states that an OEM catalytic converter warranty must be 80K miles or 8 years. So OEM units are larger and contain more precious metals than aftermarket units. Aftermarket converters aren’t held to such a stringent standard, they are warranted for only 25,000 miles.

Aftermarket catalytic converters come in two styles, direct and universal fit. A direct-fit catalytic converter is made to fit exactly onto your car’s exhaust system with no modifications. If your old converter had a flange to bolt directly to the exhaust manifold, a direct fit will also have that flange. A universal converter will not have any of those fitting. You will have to weld or bolt on all the adapters to make it fit.

Walker is one of the better manufacturers of aftermarket converters you can buy for your vehicle. Let’s use an example of a 2005 Dodge Grand Caravan with a 3.8L engine. A factory converter from the dealer lists for $642 plus a $200 core charge (they want the old converter because it can be recycled). However, an aftermarket converter costs $180 to $250. When you consider the difference in the warranties, you’re pretty much getting what you pay for. Since the OEM catalytic converter must be covered for 80K miles and the aftermarket converters only 25K miles, it makes sense that the factory units cost 3X more. The question for you, unless a catalytic converter is abused, it can last the life of the vehicle. They’re either destroyed by misfires, oil and coolant leaks, or impact. If you’re one of those people who drive around with your check engine light on, you may be having misfires without knowing. So you’re self destructing the catalytic converter. In that case, why would you spend the money for an OEM version? You’ll just destroy that too.

Can you just remove your catalytic converter

Ok, you’re a cheapskate and you don’t give a damn about the environment. So you want to replace the catalytic converter with a straight pipe, right? Or, you want to chip out the ceramic honeycomb and run the catalytic converter empty. First off, what you propose is illegal. No legitimate shop will do it because they face a $10,000 find. Second, if you do it yourself, and your vehicle is equipped with a post cat oxygen sensor, you will get a check engine light—it’ll be on full time so you’ll never know if the computer has set a different code.

©, 2015 Rick Muscoplat

Posted on by Rick Muscoplat


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