With vehicle odors, the symptom is not hard to identify. Finding the source and eliminating the problem is more difficult, but this guide may make it a lot easier.

Vehicle odors come in many forms. If the odor is not too objectionable, it may be tempting to ignore it. This is normally not a good idea as any unusual odor is normally the symptom of another problem. Treated quickly, many larger problems may be avoided.

Nine common sources of vehicle odors

A sweet smell in or outside the vehicle

Leaking antifreeze or coolant normally has a sweet smell, similar to maple syrup. Most often, leaking coolant will smell after the vehicle has warmed up and after sitting with a warm engine. If the odor is under the hood, common sources include a leaking radiator, hose or water pump.

Sometimes coolant odor may be present inside the vehicle. This often results when the heater core starts to leak. Other symptoms may include a film on the inside the windshield and wet carpet. Always check the coolant reservoir and if it is low, there will normally be a leak in the cooling system.

Coolant leaks may result in an overheated engine, corrosion in the cooling system and mildewed carpeting in the vehicle.

A smell of trash or oil burning

Engines generate heat and are lubricated by engine oil. When oil leaks, it often finds its way onto a hot surface. Burning oil will produce an odor, much like a trash fire. One of the most common sources of such an oil leak are valve cover gaskets. The valve cover is normally located above the exhaust manifold, which is very hot. Oil pan gaskets and oil drain plugs that leak may also create quite an odor.

Power steering fluid is under great pressure and is also very flammable. A tiny hole in a power steering hose can spray oil onto the exhaust and cause a vehicle fire. Like the old saying, "Where there is smoke there is fire," it is better to be safe than sorry with oil leaks. Have them checked and if there is a hazard, have them repaired to prevent problems.

Musty of mildew smell coming from vents

A musty smell from the vent is normally bacteria growing in the vents. Leaves and debris may collect at the base of the windshield, where the system draws air. Cleaning all debris from this area will often help with odors.

Air conditioning causes moisture to condense in the vents and on the evaporator core. Bacteria can grow in this dark, moist environment and cause an odor. These areas are not readily accessible and cleaning may be very difficult. Good results are often obtained with the following method.

In more persistent cases, disassembly of the unit and professional strength disinfectant may be needed. If the vehicle has a cabin air filter, replacing the filter also may help a great deal.

Rotten smell from trunk

The trunk can be a source of odors when organic items are inadvertently left inside. Food items sometime fall from shopping bags transported in the trunk. As these items begin to decay, a strong odor will be emitted. Removing the item will help, but may not eliminated the odor. Removing all mats and scrubbing the trunk with disinfectant may also help.

Water that enters the trunk will also produce odor. Leakage around tail lights are a common place water enters the trunk. Vehicles that have been wrecked, also leak at damaged seal areas and from misalignment of trunk lids. Locating and repairing the source of leakage, will often correct the odor.

Exhaust fumes

Modern vehicles should not produce exhaust fumes under normal operation. When the exhaust produces a discernable odor, there is a problem. A strong smell, that burns your eyes, is an indication of an engine running too rich. This means there is too much fuel being burned, relative to the air. A stuck injector, a bad air flow meter or a bad oxygen sensor are a few causes.

Steam, water or an antifreeze smell, coming from the exhaust, may signal a cracked cylinder head, blown head gasket or leaking intake gaskets. Continuing to drive a vehicle with such problems will do tremendous damage.

Automotive exhaust contains carbon monoxide, a colorless, odorless toxin. Unfortunately, this poison is difficult to detect. Carbon monoxide produces drowsiness and can result in death. Fortunately, the vent fan, on all newer vehicles, runs whenever the engine runs. This produces a positive pressure in the passenger compartment and helps keep exhaust out. A leaking exhaust system can override safety feature as exhaust may be drawn in at the vent intake.

A gasoline smell

Pure gasoline has very little odor. For safety, odorant is added at the refinery to give the characteristic smell. Any gasoline smell is abnormal, dangerous and should be checked. Fuel tanks are vented through the evaporative emissions systems. This prevents fumes from being released.

Gasoline smells in the area of the fuel tank is often caused by a bad or loose fuel cap. There are also several hoses and valves that may leak. The fuel tank has an entrance for the fuel pump, normally sealed by a large O-ring. Leaks may develop and fortunately, post 1996 vehicles will normally signal this with a check engine light.

Fuel smells in the engine area may be caused by leaking fuel injectors or fuel lines. This is particularly dangerous, combined with engine heat and the under hood ignition system. Small leaks may be located by adding a fluorescent dye to the fuel and checking the system with a black-light. The dye leaves a stain which is easily detected.

A mildew smell

Carpeting and interior absorb odors. Any water that leaks into a vehicle will make the matter far worse. Interiors often becomes mildewed, because air conditioning vents stop up and water leaks under the carpet. If not corrected mold may form and a very serious situation develops.

Air conditioning removes heat and humidity to make the passenger compartment comfortable. The humidity drips from the evaporator core and is channeled outside by the evaporator drain. Dust and debris may plug the drain, and water may enter the passenger compartment. One early symptom is a reduction of water dripping under the vehicle, when the air conditioner is running.

Water from the air conditioner is odorless and often runs behind the carpeting, where it may not be seen. Under the carpet mildew and eventually mold start to form. Prevention is the best plan. Keeping the cabin filter, if the vehicle is equipped, clean will help prevent dust from stopping the drain. Regularly checking carpeting for dampness, is also a good idea.

Leaks around the windshield, the sunroof and doors are also sources of water on carpeting. Once the leak is found and corrected carpeting will have to be removed for proper cleaning and drying. If the smell persists after cleaning, professional ozone treatment may help.

Professionals pump ozone the interior of the vehicle, to create a lethal concentration. The large quantity of ozone kills all organic life in the vehicle, as mildew, bacteria or mold. Such treatments take several hours and need to be administered by a trained professional. Ozone is extremely effective and safe, when properly used.

Rotten egg or sulfur odor

Hydrogen-sulfide is a byproduct of gasoline and is supposed to be controlled by the catalytic converter. One way in which a catalytic converter fails releases this gas and a rotten egg type of odor. Improper fuel/air mixture, caused by failure of the computer management system, is the leading cause. Caught early, the converter can sometimes be saved.

Catalytic converters are very expensive and some vehicles use several. The converter is covered by an EPA mandated, eight-year or 80,000 mile warranty. Beyond that time or mileage replacement is usually very expensive.

Gear oil, used in differentials and some transmissions, also contains sulfur as a lubricant. Leaks from these components, sometimes get onto the exhaust and produce a burning sulfur smell. This may also be accompanied with smoke from under the vehicle, in a few cases.

An acrid burning smell

Brakes stop a vehicle by friction and friction produces a great amount of heat. Hard braking and applying brakes to slow the vehicle when going down hill, can cause brakes to burn. Overheated brakes produce a strong burnt smell, similar to textiles burning.

Driving with the parking brake applied is another source of brake overheating. Parking brakes should always be fully applied when set. This helps prevent, forgetting they are on and driving with them applied. The cables used to operate parking brakes sometime stick and the brakes will stay applied, even though released.

Several problems with brakes, such as sticking calipers, bad brake hoses and contaminated brake fluid can also cause brakes to stay applied. The tremendous heat generated quickly damages the brakes. One early symptom is warped brake rotors and a steering wheel that shudders when braking.

Another symptom of brake overheating, may be a lower than normal brake pedal. The heat generated may cause brake fluid to boil and we can lose brakes. Placing the hands near each wheel will normally show one or more wheels much hotter than the others. Immediate repair is necessary to prevent damage and possibly losing our brakes.

Sometimes plastic shopping bags stick to the vehicle exhaust and are often confused with the smell of burning brakes. These plastic bags are very light and the wind often carries them through shopping center parking lots. The heat of the exhaust causes them to stick, where they melt and produce a huge amount of odor. Fortunately, scrapping the remains from the exhaust usually solves the problem.

Smells are a useful diagnostic tool. Paying attention to the normal smell of a vehicle, helps bring attention to changes. Quick action, when smells change, can save a bundle.

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