An exhaust system is a complex assembly, which has a number of functions to perform. The system must:
- Carry engine exhaust gases safely to the rear of the vehicle
- Reduce the engine sound level
- Maintain engine performance
- Reduce or eliminate certain engine emissions
The space available under the vehicle determines the configuration of the total exhaust system. Because each automobile design is different, exhaust systems must also be different.
An incorrectly designed exhaust system could restrict the flow of gases and, if the restriction is excessive, can cut horsepower, reduce gas mileage and performance, and potentially damage the engine. This restriction is one of the dangers faced when components used are not part of an exhaust system specifically designed and engineered for a particular application.
The life of an exhaust system is extremely difficult to determine. Many factors, including regional climate, the type of driving, and whether the system is single or dual, are involved. As a rough rule of thumb, however, a typical life expectancy of a premium aftermarket exhaust system should be in the neighborhood of two to three years depending on driving habits and the previously mentioned factors.
A major cause of exhaust system part failure is internal corrosion resulting from acidic moisture which is chemically produced by the combustion of air and gasoline in the engine. Because these acids are in contact with the inside of the exhaust system, the deterioration of these parts occurs primarily from the inside out.
Acid moisture is most destructive when both the engine and the exhaust system parts remain cold. When the engine and exhaust system are fully warmed up, the hot gases coming through the exhaust system evaporate the condensed acid and send it out the tail pipe. As a result, those parts closest to the engine heat up first, stay warmer longer, deteriorate more slowly than the parts farther back in the system. Consequently, exhaust manifolds, pipes and catalytic converters tend to have a much longer life expectancy than exhaust pipes, mufflers or tail pipes.
Because of the acids produced during combustion, the exhaust system is one of the very few parts on a vehicle that continues to wear even though the engine is not running and the vehicle is stopped. This acid deterioration of exhaust parts, along with driving styles helps explain the extreme variations in exhaust system life even within the same climate zone.
Exhaust systems also fail from external corrosion caused by the salt and other chemicals used on the roads in the winter for traffic safety.