Exhaust System - Maintenance
Exhaust System Topics
  1. The Exhaust System
  2. Rules for Replacing Catalytic Converters

The Exhaust System

The longevity of muffler and pipes depends on what kind of steel the components are made of, how pipes are routed under the car, where the muffler is located, and whether or not the vehicle has a catalytic converter.

Original equipment pipes made of aluminumized steel generally last five to seven years, except in areas with a lot of road salt and moisture. In these areas, pipes may need replacing after three to five years.

Original equipment pipes made of stainless steel (which are used from the converter forward on most cars and for the entire exhaust system on some) can last up to 10 years or more. Most aftermarket pipes, by comparison, are made of ordinary steel which is good for about three to five years of service. Aluminumized and stainless pipes are better, but cost more.

With mufflers, stainless holds up the best, followed by doublesided galvanized steel. Single-sided galvanized and aluminumized hold up fairly well, while plain steel offers little or no corrosion resistance.

As a rule, the hotter a muffler runs the longer it lasts. Mufflers on vehicles with catalytic converters run hotter and last longer than those on older vehicles without converters. Mufflers located ahead of the rear axle last longer than those located aft of the rear axle.

Mufflers rust from the inside out. Rust is caused by moisture in the exhaust. Moisture condenses in the muffler when the engine is shut off and the muffler starts to cool. Some mufflers have a small pin hole that allows condensation to seep out.

One aftermarket muffler manufacturer puts a small packet of a special moisture absorbing chemical inside some of their mufflers to fight internal corrosion.

A muffler that needs replacing is an opportunity to sell clamps, pipes, hangers and any special tools that might be needed to complete the job.

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Rules for Replacing Catalytic Converters

What Is A Catalytic Converter?
A catalytic converter is part of the exhaust system and uses a catalyst to convert three harmful compounds in automobile engine exhaust into harmless compounds.

The three harmful compounds are:

Carbon monoxide is poisonous, nitrogen oxides lead to smog and acid rain, and hydrocarbons produce smog.

In a catalytic converter, the catalyst (platinum and palladium) is coated onto a ceramic honeycomb or ceramic beads that are housed in a muffler-like package attached to the exhaust pipe. The catalyst helps to convert carbon monoxide into carbon dioxide. It converts the hydrocarbons into carbon dioxide and water. It also converts the nitrogen oxides back into nitrogen and oxygen.

Original equipment converters on new cars and light trucks are currently covered by an eight year/80,000 mile emissions warranty. Motorists can return to the new car dealer for free replacement as long as the converter is covered.

The customer can choose to have an independent repair garage replace the converter at his own expense if it is still under warranty. Once the vehicle is out of warranty, he pays to have it fixed no matter where he takes it.

The converter should go at least 100,000 miles on most late model vehicles. Trouble is rare unless the converter has been lead fouled (by using leaded gasoline), damaged by overheating (often due to unburned fuel in the exhaust from a misfiring spark plug or leaky exhaust valve), or removed.

Rendering A Catalytic Converter Inoperative Is Illegal
Removing the converter and replacing it with a straight pipe is illegal. The new Clean Air Act makes anyone (including the motorist himself) liable for a $2,500 fine if he or she removes, disconnects or renders inoperative any emission control device.

Other Rules and Procedures
If the vehicle has flunked an emissions test and the cause is determined to be a bad converter, or if the converter is clogged, damaged, lead-fouled, rusted out, physically damaged or missing, it is legal to replace it. Federal law prohibits aftermarket garages from replacing converters as long as they're under the five year/50,000 mile emissions warranty, unless any of the previously-mentioned reasons exist for replacement.

The shop must first document the reasons, along with the vehicle's odometer reading, and have the customer sign it before the converter is replaced. The shop must keep the old converter for 15 days and the paperwork for six months. The replacement converter must be the same type as the original (two-way, three-way or three-way plus oxygen), be EPA-certified, and be installed in the same location as the original.

Aftermarket replacement converters meeting EPA requirements must have a minimum lifespan of 25,000 miles, and include a five year/50,000 mile warranty covering exterior shell and welded pipes against defects in materials and workmanship.

Used converters are no longer allowed unless the supplier can certify the converter is still capable of cleaning up 50% of the unburned hydrocarbon (HC) and carbon monoxide (CO) emissions within two minutes of start-up, and 75% of the HC and CO emissions within 200 seconds.

All approved replacement converters are required to carry a permanent label that identifies the type of converter (N for new, U for used), a code number issued to the manufacturer by the EPA, an application part number, and a manufacturing date.

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