Why am I Smelling Exhaust Fumes From My Car?

A car can emit a range of smells while operating, most of which are normal and not a cause for concern. Light exhaust odor is one of these common smells. For the most part, you can expect some exhaust odor from the outside of your car, but modern emissions systems greatly reduce the quantity of harmful gas emitted during operation, which means less overall exhaust smell. However, if you notice excessive exhaust odor, it’s safe to assume that something probably isn’t right. 

What is Considered “Normal” Exhaust Odor?

Engine emissions never exactly smell good, but when your car is running normally the smell should only be detectable around the tailpipe and put off a slightly musty, acrid smell. If you are starting your car on a cold morning, the emissions may smell more like gasoline. Fuel is not atomized efficiently in a cold engine, so more fuel is used to keep the engine combusting properly. Excess fuel is called “running rich”, and this condition should clear up once the engine is at operating temperature. You should never have a persistent exhaust smell in the cabin of your car. 

Exhaust Leak

The most common source of an exhaust odor is a leak. Exhaust leaks occur when the exhaust system has a hole or crack that allows exhaust gasses and sound to escape before the tailpipe. 

These leaks can occur in any portion of the exhaust but are most commonly seen in components such as the muffler or resonator, or along a gasket or weld within the system. Leaks most often develop due to rust, damage from collisions with rocks and debris, or faulty fabrication. 

Muffler and tailpipes

While the actual issue is simple, finding it can prove more difficult. Leaks can be hard to locate, especially when they’re smaller in size. However, most auto repair facilities can diagnose the source of the leak through the use of a smoke machine. By running thick white smoke throughout the system, the leak can be located from the smoke exiting through it. 

Exhaust leaks may cause the engine to sound louder, more aggressive, and less smooth. If the leak is located in the midsection of the exhaust system, both the sound and smell will be more noticeable as they leave the exhaust system right under the cabin and make their way into the interior of the vehicle. 

The effects of a leak go beyond simply being annoying though. Oftentimes exhaust leaks will cause untreated gasses to leave the system and enter the atmosphere. Vehicles with exhaust leaks will almost always fail emissions testing. Depending on where the leak is located,  it can also harm the vehicle mechanically, as it can cause extra oxygen to enter the exhaust system. With the oxygen sensors reading an increased reading, extra fuel will be added to the engine to compensate. As the engine will be unable to combust all of the gasoline, some unburnt fuel will enter the exhaust. This can lead to failures of both the catalytic converter and oxygen sensors as they eventually become coated in unburnt gas.

Exhaust leaks should be taken care of promptly, as leaving them over time will only lead to further risk of damage. Some can be patched, while other cases may require a full replacement of that component or exhaust section. 

Rich Air Fuel Mixture

On the topic of unburned fuel, this can also cause a strong smell around your vehicle. This can happen due to either an excess of fuel being injected into the engine, or a lack of air intake causing the ratio to be thrown off. As the gasoline makes its way into the exhaust system, it will partially burn off and can cause a thick black smoke with a pungent gasoline aroma to exit the tailpipe. 

So if your vehicle constantly smells like a gas station, you should bring your vehicle in for an inspection. In rare cases, this could mean a fuel leak (which is extremely dangerous), but most times it comes down to the air-fuel ratio. For the same reasons as an exhaust leak, this can be problematic for sensitive exhaust components like the catalytic converters, sensors, and the health of your engine. 

A rich air-fuel ratio can occur for several reasons. A blocked engine air filter or vacuum leak may restrict the intake of air to an unhealthy amount while leaking fuel injectors or a faulty reading from the mass airflow sensor can cause an excess of fuel to throw off the balance. Remember, an exhaust that smells like fuel should only be a concern when the engine is at operating temperature, not when starting a cold engine. 

Catalytic Converter Problems

If you smell a distinct “rotten egg” smell from the exhaust of your vehicle, you most likely are experiencing a catalytic converter failure. Hydrogen sulfide is a byproduct of combustion in your engine and smells strongly of sulfur. When your catalytic converter is damaged, your exhaust gasses will contain a much higher amount of these harmful compounds, including the pungent hydrogen sulfide. 

A failing catalytic converter not only leads to an unpleasant odor, it can cause a whole host of other issues. Your performance and efficiency may be noticeably reduced, and your vehicle will be unable to pass emissions testing if your area requires it.

Catalytic converter under car
Ballista, CC BY-SA 3.0 http://creativecommons.org/licenses/by-sa/3.0/, via Wikimedia Commons

Exhaust Service and Repair in Tucson

If you experience excessive or unusual smells from your exhaust, have it inspected by a trusted professional immediately to keep you safe and avoid further damage. 

The ASE-certified technicians at Micro Import Service have the expertise and equipment to properly patch your leak or replace the failed component. Call or schedule online with us today!