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Troubleshooting by Smell

Facts about your olfactory

In our first article, we established that your car "talks" to you in a variety of ways, and covered how to use your sense of sight to diagnose mechanical problems. Now how about smelling your car? It's no secret that vehicles produce a rich variety of aromas. Rather than dismissing them as unpleasant or annoying, they may be telling you something important about your car's condition. As with the article about the sense of sight, we are primarily concerned with smells emanating from under the hood, with emphasis on identifying fluid leakage. We will also cover various causes for under-car odors, as well as exhaust and braking system odors.

Indicators

Smells usually accompany the malfunction of a component that contains or runs on fluids. Often, the smell will be more obvious than any other sensory clue, such as from gasoline leak. (Incidentally, gasoline by itself doesn't smell much, so the government requires a specific scent be added for safety reasons). Getting familiar with the smells of your vehicle's lifeblood is essential. And it's good to know how a specific fluid may differ in aroma, whether new or old/worn, cold or hot. You'll find it useful to know how they smell when coming into contact with a hot exhaust system. It's like the value of knowing the difference between what food smells like when it's fresh or spoiled.

Radiator coolant has a somewhat sweet, yet definitely chemical smell to it. Whether it is leaking under the hood, on the interior carpet, dripping on a hot exhaust system, or going out the tailpipe, it has pretty much the same smell. If your engine is experiencing an intermittent coolant loss, but a coolant smell from under the hood is noticed only during warm-up, suspect a malfunctioning water pump or possibly a radiator problem.

The smell of other fluids leaking from under the hood is hard to detect from the driver's seat, unless they are dripping onto a hot exhaust system. All of the petroleum-based fluids smell about the same—an acrid/burnt odor—whereas mineral-based power steering fluid will smell a bit more "nutty." If these smells are only noticed after more severe engine loading, the leak(s) are in their early stages, but should be checked out to assess their relative degree of hazard. When an immediate fix is not called for, you can then estimate (and prepare for) future repair costs.

Noisy Smells

A burning rubber smell from under the hood that's accompanied by a squealing sound that changes in pitch as you accelerate probably indicates that you have a slipping accessory belt, possibly due to high rotational resistance in one of your accessory components. Alternators, water pumps, air injection (smog) pumps, air conditioning compressors and other engine accessories have all been known to "seize" or fail by ceasing to turn.

Depending on which component has seized, and what type of a drive-belt configuration your vehicle has, it may be possible to do an "in-field" procedure (cutting the belt) in order to allow you to drive a short distance to a repair facility. If your vehicle has a single "serpentine" drive belt, or the water pump has seized, regardless of what type of belt-drive system your vehicle has, it's tow time. Otherwise you may severely overheat your vehicle's engine by driving even a short distance.

Rotten Smells

Normally exhaust should not smell offensive, and almost could be described as somewhat pleasing. If it smells acrid and makes your eyes water, likely the catalytic converter is not working. A poorly running engine may accompany this smell and will make a catalytic converter overheat, and give off a sulfur odor out the tailpipe. When you encounter this "rotten egg" stench, the "service engine soon" malfunction indicator lamp will likely be illuminated. The converter may appear red-hot as well, and immediate attention is required!

Of course, anytime you smell exhaust while you're driving, and you've determined that your vehicle is the source, a thorough inspection should be done as soon as possible to avoid breathing any carbon monoxide (which has no aroma). To ensure adequate ventilation of the exhaust fumes, it's not a bad idea to roll down all of the windows before heading to your mechanic. If the smell becomes more intense, park the vehicle and have it towed to your mechanic, as concentrated exhaust fumes are toxic.

Can't-Tell Smells

An exhaust system running at a normal temperature, although not red-hot, is still frying pan-hot, especially adjacent to the catalytic converter. This fact can make for unusual odors if road debris gets lodged nearby the system. So if you would swear that you smell something that is not typical of anything normally generated from your vehicle, don't just blow it off as an anomaly that doesn't concern you, especially if the smell stays with your vehicle for some time.

A good candidate for this kind of "red herring" scenario would be one of those ubiquitous plastic shopping bags that decided to stick itself to your exhaust system as it was passing under your vehicle. This is not at all uncommon, although chances are that you might think that there is a more serious cause than there actually is. Unscrupulous mechanics have field days with such problems, sad to say.

Too-Hot Smells

Overheating brake or clutch lining material has a distinct odor as well—somewhat like a burnt synthetic fabric, of which the lining material often consists. Some of this smell is normal after very heavy use, yet can be indicative of a more serious problem which would require immediate attention. Parking the vehicle and checking for the strength of the smell at each wheel will tell you at which one has a problem.

There is no question that a seasoned vehicle "sniffer" will put you on the scent of trouble, sometimes long before it becomes a crisis. So use your olfactory senses to give you more time and a wider range of solutions to a mechanical problem.