Odors and smells are often a sign of trouble. Here is a quick guide to what your nose might be telling you:
Burning Plastic Smell
This could be coming from a wiring short or an electrical fire. Or, if somebody just flicked a cigarette out the window, it may have blown back in the window and is burning the carpeting or upholstery in the back seat. Better stop and investigate.
Antifreeze has a sweet, almost pleasant odor. But it usually means your engine or cooling system has a coolant leak. Check the temperature gauge to see if the engine is getting hot.
If you see any steam coming out from under the hood, stop and shut the engine off.
CAUTION: If you open the hood to investigate, be careful because hot steam can burn you. Let your vehicle sit and cool down before you attempt to add coolant or stop leak to the cooling system.
Coolant leaks can also occur inside the car, in the heater core under the dash. A leak here may form a wet spot on the carpet on the passenger side.
Smells Like Burnt Toast
This usually means the engine has an oil leak, and oil is dripping onto a hot exhaust manifold or exhaust pipe. A small leak is nothing to worry about, but you should check the engine oil dipstick to make sure the oil level is not getting too low. The fix is to replace the leaky gasket or seal that is allowing oil to leak out of the engine.
A similar smell can also be produced by burning automatic transmission fluid if the transmission or transmission oil cooler is leaking oil onto a hot exhaust pipe. This type of leak will require an undercar inspection. The source is often a leaky transmission pan gasket , input shaft seal or driveshaft seal, or pipe that connects the transmission to the oil cooler in the radiator.
If you are following a diesel truck, bus or school bus in traffic, the fumes are entering your car through your heating ventilation and air conditioning (HVAC) system fresh air inlet, or your side windows if they are open. Roll the windows all the way up, and choose RECIRC if your HVAC system has a button or selection for recirculation mode. This will block off the outside air and reduce the odor.
If your car or truck has a cabin air filter, noticing outside odors is a symptom that the activated charcoal in the cabin air filter has probably reached the end of its service life. Activated charcoal can absorb odors, but it only lasts about a year or so. Better check your cabin air filter and replace it with a new one if it is more than a couple years old. See your Owners Manual for the location of the cabin air filter (it is usually buried behind the glove box or is located in the cowl area at the base of the windshield).
Carbon Monoxide Smell
Unfortunately, carbon monoxide has no odor. You might smell exhaust fumes, but you can't smell or see carbon monoxide fumes (which are a component of exhaust). Carbon monoxide fumes mean your exhaust system is leaking. This can be very dangerous, especially during cold weather when the windows are closed, because carbon monoxide can make you dizzy or even overcome you before you realize what is happening. If your car has an exhaust leak, get it fixed.
Musty Mildew Odor
If you get a blast of musty odor that smells like a men's locker room or a pair of dirty socks when you turn on the air conditioner, it means mold and mildew is growing on the surface of the A/C evaporator inside the HVAC system. The evaporator is very difficult to get to, so there is no easy way to clean or replace it. You can try to spray an odor-killing aerosol like Lysol into the A/C ducts and into any openings you can find in the HVAC housing under the dash, but it may take a professional odor treatment to get rid of the smell. A special long spray wand can be used to snake inside the HVAC housing to spray deodorizer and/or biocide directly onto the A/C evaporator. Mold grows here because it is a wet and dark environment.
New A/C evaporators may have a special chemical treatment or anti-bacterial coating to inhibit germ growth.
Some vehicles have an "afterblow" feature in the HVAC system that keeps the fan blowing for a short period after the ignition has been turned off. This helps dry the A/C evaporator. If this feature is not working, moisture condensation on the evaporator can create conditions that are ripe for mold growth.
If you smell a musty odor all the time inside your car whether the A/C is on or not, you probably have wet carpeting because of a water leak around a window seal, or because the drain hose from the A/C evaporator is plugged and is spilling water inside the car and onto the carpeting. This same type of odor often occurs as a result of flood damage and can be very difficult to remove. You may have to replace the carpeting if you can't dry it out and mask the smell with air freshener.
Rotten Egg Odor
Gasoline contains a small amount of sulfur, and when you first start your car you may notice a rotten egg or sulfur smell. The smell is produced by the catalytic converter as it converts the sulfur into hydrogen sulfide. This is normal for some cars, but may be worse if the brand of gasoline you are using contains higher than average levels of sulfur.
Danger! If you smell gasoline inside your car, the fuel tank or fuel lines may be leaking. This can be a very dangerous situation. Stop and get out of the car, then look underneath for any signs of fuel leakage. If the odor is strong, it might be wise to have the car towed to a repair shop for repairs rather than risk driving a potential fire bomb!
If your car catches fire, stop, get yourself and any passengers out as fast as you can, and get as far away from the vehicle as you can. Call 911. Let the fire department deal with it. Do NOT open the hood or attempt put it our yourself. Gasoline fires can spread very quickly, and there is always the danger of the fuel tank exploding!
New Car Smell
That unique new car smell that you often notice inside a brand new car is not necessarily a good thing. The smell comes from volatile organic hydrocarbons (VOCs) that are slowly evaporating from the plastics and carpeting inside the car. Some of these compounds are known carcinogens that can cause cancer! See the Healthy Car Report for a summary of which cars produce the highest levels of VOCs from their upholstery and interior plastics.
If you just bought a new car and it smells unusually strong inside, it might be a good idea to leave the windows partially open when the car is parked (preferably while it is parked inside your garage so some lowlife does not break into it). The VOCs that are evaporating from the upholstery and carpeting will form a haze on the inside of the windows, as if someone had been smoking inside your car. Just remember, you are breathing this stuff every time you are inside your car until it eventually goes away (which may take up to 6 months or more!).
Suffocating Obnoxious Odor
You are probably driving down wind of a hog farm or a municipal sewage treatment plant. Hold your breath, plug your nose, and step on the gas until you are out of range. Also, replace your cabin air filter because it isn't stopping the smell.
That bean burrito you had for lunch may be catching up to you. Nothing is wrong with your car. Roll down the windows and turn on the A/C to blow out the smell. If a passenger is the guilty party, lower their power window to pull the odor their way.
Smells Like Curdled Milk
It probably is. You kids may have spilled their milk in the back seat and forgot to tell you. Food and liquids spilled on the seats or carpeting can produce very unpleasant smells, especially during hot weather. Get some carpet or upholstery cleaner and clean up the spill as best you can, then mask what's left with some air freshener.
Really Nasty Dead Fish Smell
Somebody doesn't like you and has played a nasty trick on you. Check under the seats for a dead fish.
Air fresheners are available in a wide variety of scents these days, and come in many different styles. Choose one that you find pleasant to take the edge off your drive.
Many air fresheners come with a hook or loop of string so they can be hung from your rear view mirror. But police don't like this because it obstructs your vision. People have actually been stopped and ticketed for this! Better hang your air freshener in a less obvious location.
Air fresheners are also available that mount over the A/C ducts and release a scented perfume. These are good if your car has a tendency to develop an A/C evaporator odor during damp weather.