What Makes a Car Smell Bad?

car smells bad
Rolling down the window might provide relief from a car that smells bad, but you still need to track down the source of the odor. Philipp Nemenz / Cultura Exclusive / Getty

When your car first rolled off the showroom floor, it had what is colloquially known as that new car smell. This new car smell is caused by volatile organic compounds (VOCs) that seep out of plastics, vinyls, and other materials inside your car. Once these materials have more or less finished off gassing, the new car smell is gone, and you're not going to get it back.

That doesn't mean you have to just sit back and take it when your car starts smelling bad. There are a lot of different reasons a car can smell bad, and some of them are pretty easy to deal with. Others are harder to knock out, but even if you're never going to recapture that new car smell, rest assured that there are ways to deal with every bad car smell out there.

Some causes of bad car smells are mechanical in nature, and having the problem fixed will eventually do away with the smell. Other smells can be dealt with by airing your car out, turning to a low tech solution like baking soda or charcoal, or going high tech with an ionizer or air purifier.

Tracking Down Your Bad Car Smell

While there are countless different reasons a car might smell bad, they fall into two basic categories: smells associated with a mechanical issue and smells with an outside cause.

Unpleasant odors associated with mechanical issues can indicate a failing heater core, malfunctioning catalytic converter, leaking oil, and a host of other issues. Outside sources can include everything from cigarette smoke to an orange that rolled under the seat six months ago.

If you have a mechanic you trust, you can take the guesswork out of this whole process by just taking your car in for a once over. In the same way that a good tech can often diagnose a problem just by listening to it, most experienced mechanics can take a quick sniff and tell you whether that acrid smell is a burnt clutch or the remains of someone’s sack lunch that got lost in the back seat.

Here’s a quick rundown if you want to try diagnosing your bad car smell at home:

  • Sweet smells
    • Typically indicate a leaking heater core.
    • If the windshield fogs up, and it can't be wiped without smearing, that's another hint that the heater core is leaking.
    • If it starts out sweet and turns bad, then someone might have spilled something.
  • Moldy smells
    • Water is getting in your vehicle somehow.
    • Likely the A/C evaporator.
    • Could also be window seals or another issue.
  • Acrid smells
    • Indicates burnt clutch or brake material.
    • Caused by riding the clutch or brakes.
    • Also caused by a slipping clutch.
    • Clutch could be worn out or need adjustment.
  • Burnt oil smells
    • Oil is likely dripping onto the exhaust manifold.
  • Gas smells
    • If the car has a carburetor, expect some gas smell after shutoff.
    • In newer cars, smelling raw gas indicates an issue.
    • You’ll have to locate the source of the gas and fix it.
  • Sulfur smells
    • Bad catalytic converters sometimes smell like rotten eggs.
    • Manual transmission and transfer case oil sometimes smells like this when old.

Regardless of what the source of the bad smell is, if it’s caused by a mechanical problem, then the solution is to fix the problem. In some cases, like oil that’s leaking onto the manifold, the smell will often persist after the problem has been fixed. However, it will eventually go away.

Dealing With Other Bad Car Smells

Like mechanical failures that cause bad car smells, the fix for other offensive odors is to remove the source. If you’re dealing with a cigarette smoke smell, or something like a baked-in wet dog smell, then the source is obvious. If it’s a mystery odor that can’t be tracked down to a mechanical failure, then you’ll have to get down and look under the seats, in the trunk, and everywhere else.

Once you’re sure there aren’t any lost groceries rolling around under the seats, you can start thinking about removing the smell.

Potential solutions include old standards like baking soda and charcoal, while high tech options include air purifiers, ionizers, and even having your car treated by an ozone generator. You can also mask the smell with an air freshener, but that’s a temporary measure at best.

Absorbing Bad Car Smells

Baking soda and charcoal are both substances that can be used to absorb bad smells, and they work in cars just as well as anywhere else. For instance, if the carpet in your car smells, you may want to try spreading on some baking soda, letting it set for a while, and then vacuuming it up.

Charcoal is even easier to use, since all you have to do is place it in your car and leave it there for a while. The charcoal will absorb bad odors, after which you can remove it. In some cases, that may be all you have to do.

Ionizers and Purifiers for Bad Car Smells

Car air ionizers work by emitting ions, which purportedly results in the molecules that make up allergens and odors stick to surfaces rather than float around in the air. Purifiers actually take in air from your vehicle’s interior, pass it through a filter, and capture impurities that way. Your mileage may vary with both of these devices depending on the severity and source of the smell that you’re dealing with.

Getting Back That New Car Smell

Once your new car smell is gone, your car won't ever smell exactly like that again. You can buy air fresheners that claim to have a new car smell, but they don't. There are also deodorizing products that also promise to impart a new car smell, and they work better, but it still isn't exactly the same.

Part of the problem is that different cars have different new car smells, which is caused by the variety of materials that contribute to the smell. Vehicles with leather seats smell different from cars with cloth seats, and vehicles from different manufacturers each have their own unique scent.

The closest you're likely to get to returning your vehicle to its factory fresh state will require a thorough cleaning. You must first remove all odors and odor sources, so that the vehicle smells totally neutral. If you shut it up tight, and leave it locked up in the sun for a few days, the natural odors of the seat, carpet, trim, and other materials will begin to reassert themselves.

It won't be the same, but that's probably as close as your car will ever get to smelling new again.