Catalytic Converter Cleaning

by Ian Kenney

Kids in the United States who reach driving age today probably don't remember acid rain and smog alerts. Those problems still exist, but their frequency and intensity have been mitigated, due in part to the catalytic converter, a clever little device developed by French engineer Eugene Houdry. He identified a growing problem in the smog heyday of the 1950s, but his invention wouldn't become standard equipment in most U.S. autos until the 1970s. Catalytic converters achieve their results efficiently with minimal power loss in today's cleaner-burning engines, but they can become clogged, or "poisoned," and that requires immediate attention.

What Is a Catalyst?

Catalytic converters are made up of a substrate, usually a ceramic honeycomb that maximizes exposed surface area, and a metal catalyst like platinum, rhodium or palladium that reacts with exhaust contaminants. Unburned hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxide gas (NOx) are the big three baddies that the catalytic converter eliminates. Signs that your converter may be failing include sluggish throttle response, stalling at high temperature or a persistent sulfur smell coming from the tailpipe.


The service life for most OEM converters exceeds 100,000 miles, so if your lower-mileage car's exhaust contains higher-than-accepted levels of HC and CO, the converter is fouled due to a problem elsewhere. There are contaminants that "poison" the reactive surface of the honeycomb. Lead is a converter killer, and while it was banned in gasoline in the 1970s, it is still found in some engine additives. Phosphorous and silicone are culprits also. Phosphorous is found in motor oil and can find its way to the converter if your engine is drawing oil into the combustion chamber. Silicone comes mainly from a leak that causes coolant to burn in the engine and exit to the exhaust systems. Both of these are engine problems that ruin the converter, not converter problems that ruin the engine.


A simple Internet search returns a host of products that promise to clean your catalytic converter. Some of these are temporary fixes designed to fool emissions-testing equipment. That gets you exactly nowhere in terms of fixing your vehicle. The consensus among mechanics is that you don't clean a catalytic converter--you replace it. Magical additives will cost you money, delay the inevitable and divert your attention from the real problem, which could be as severe as a failing head gasket that leaks coolant into the engine. Let that one go for a while, and you'll be replacing your entire head at a cost of thousands. The bottom line is to be aware of the messages your car is sending. If your converter is indeed bad, either it has reached the end of its useful life or it is failing prematurely due to another engine problem. Don't get cute. It will cause you headaches down the road.

The Good News

One thing people never do is ask the mechanic to show them their old part when something has been replaced in their cars, which mechanics are required to do by law. This protects consumers against fraud. In the case of the catalytic converter, however, it can also net you some money. You own the failed converter, so you're entitled to take it with you and sell it for scrap. It's full of precious metals, so selling it to a scrap yard can help defray some of your repair costs. Also, the EPA mandates that warranties of up to 8 years and 80,000 miles be given on certain exhaust components. If your problem is the result of a defect, and your converter has failed earlier than it should, your repair cost could be covered under warranty.

About the Author

This article was written by the It Still Runs team, copy edited and fact checked through a multi-point auditing system, in efforts to ensure our readers only receive the best information. To submit your questions or ideas, or to simply learn more about It Still Runs, contact us.