Examining The Exhaust SYSTEM

By P Sanchez

Maintaining a good running exhaust system isn’t always a priority concern among car owners. But just because a typical exhaust system (at least one from a naturally aspirated engine) does not have any moving parts, it’s easy to think that the exhaust system is less prone to failure. To an extent it is true but at the same time, the exhaust system is also directly affected by the health of the engine as well as external factors. A bad engine and specific environments can ruin an exhaust system.

But how can you (or a mechanic) tell? In this article, we’ll talk about a few ways an exhaust system can be diagnosed for problems

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The primary function of the exhaust system is to provide a practical and safe way out for the exhaust gases. That’s how tailpipes came to be. But if you’re starting to smell exhaust gas inside the vehicle, the exhaust pipe may have sprung a leak and gases in the under-body are finding their way into the cabin.

Smelling exhaust in the interior is more than a nuisance, it could be dangerous. Internal combustion engines are not exactly known for harmless emissions. Quite the contrary. Take carbon monoxide (CO). Although strides have been made in greatly reducing the poisonous gas from car exhaust, it had not been totally eliminated and as such, still poses as a risk. As per the CDC, there are about 400 deaths from CO poisoning every year in the US, many of those vehicle-related. Never run a vehicle in an enclosed space without ventilation, and always have your exhaust system checked by an auto repair shop every year.

Another important function of the exhaust system is engine noise reduction. If you’ve ever been to the races, whether drag strips or motorways where sonic pleasantry is the least of anyone’s concern, you’ll know how loud “naked” internal combustion vehicles can be. We’re talking about decibel levels of above 90 dB, the threshold before sound becomes literally deafening. The need for quieter running engines necessitated the invention of the muffler. As their name suggests, this device muffles the sound to agreeable levels. In fact, a lot of places make it illegal to run a car without it. Again, damage and breach in the exhaust piping or its components can cause your exhaust to suddenly sound louder and harsher.

Granted that present-day coatings and materials made car exhausts less susceptible to corrosion, it doesn’t make them completely impervious. Tires can flick up rocks and gravel while driving which often hit the under-body of the car. They can cause deep scratches in the protective coating of metals, including that of the stainless steel material of the exhaust pipes. If the scratches are deep enough, they can expose the base metal where corrosion can start. Another particular problem is road salts used to clear winter roads. Road salts are corrosive if left on the surfaces of the undercarriage for a length of time. 

Smaller holes in the exhaust system can be patched up by sealants or spot welds. Surface level corrosion can be sanded off and the surface retreated with a protective layer as long as the corrosion has not compromise the structural integrity of the pipes. Large extent damage may require replacement of tube sections, sometimes the entire exhaust system.

Another cause for concern is hearing rattling noises in the under-body when driving through rough and bumpy roads. In this case, the exhaust system hangers are probably damaged and need replacing. Hangers are the metal and rubber attachments of the exhaust pipes to the under-body. They allow for some movement and vibration but when worn out, are the source of excessive metal rasping and rattling noise.

Perhaps the most important part of the exhaust is the catalytic converter, or “cat”. Without it, all gasoline or diesel-fed vehicles will not pass today’s strict emission requirements. “Cats” reduce harmful emissions by at least 90%. But since engines run worst over time, they tend to foul their catalytic converters, reducing conversion efficiencies, sometimes even clogging them.
If your car quickly overheats and refuses to go at highway speeds (excess of 40 mph), it might be suffering from a bad cat. In such cases, check with a mechanic.

Mechanics determine catalytic converter issues by using scan tools that specifically indicate error codes for the cat, and also by running pressure tests before and after the cat. High pressures mean the cat is clogged and gasses have difficulty escaping. A mechanic may recommend having the cat removed for ocular inspection, and if luck would have it, cleaning would suffice. Note that a clogged or fouled cat is an indication of engine trouble, so to make any lasting fix, the engine has to be diagnosed and repaired too.

Diagnosing and cleaning a dirty cat may just cost a couple of hundred dollars in mechanic’s labor but a cat that’s totally shot and needs replacement could go upwards a few grand. Like any part of the car, maintenance and early diagnosis of trouble are the keys to avoiding costly repairs.