One of the things I love most about cars as human-made objects we should be uncomfortably obsessed with is that they’re very full sensory experiences. There are strong visual elements, a huge auditory component, so many good surfaces and materials to touch, the feelings of motion and speed and vibrations — so much there for all the senses.

Including smell! In fact, smells are crucial to car ownership, and this olfactory element deserves discussion.

Smell is such a key part of automobiles and is also the part that’s by far the hardest to convey via any of our mainstream electronic media, since we have yet to develop an effective method of smell transmission or broadcasting, This lack of a stench-based media is arguably humanity’s greatest failing. Arguably.

Cars communicate a surprising amount about themselves via smell. This can include rough age (new-car smell is a thing, after all, and there’s that particular musty old-car smell), the materials used in construction and their condition. Some cars just have their own remarkably distinctive smells — I’m pretty positive I could identify an air-cooled Volkswagen just by smell, and I’m pretty sure I’m not alone there.

Look, I’m going on about this because I realized I’ve been taking for granted how my cars smell for a long time; all of my old heaps have their own smells that I know and rely on to communicate that everything is working as well (or poorly) as I expect. Once you learn your car’s default smell, any deviation should get your attention immediately.

But, objectively, this is not an obvious thing! I was reminded of this when I saw this important tweet:

Holy crap, Jack Daniel there makes a very good point — to people just getting into cars, why should they expect that stench would figure so prominently? Sure, for things like cooking or gardening or other exciting biological pursuits you may expect a big smell component, but for something technological?

With that in mind, here’s a little guide to some of the more common car-stinks you’re likely to encounter, along with our pained attempts to describe the smells. Describing smells is tricky. I mean, I can say something smells like an aroused accountant, but how do you convey that to someone who never had to ride in a car with my Uncle Larry?

Melting-Plastic Type Smells

If you strongly smell the headache-inducing smells of melting plastic, you’re almost definitely dealing with an electrical issue. These smells can often be more intense and obvious because they may actually be happening inside the car, coming from within or under the dash.

This also means you might actually see some smoke curling up from the defroster vents or someplace, too. I had an excitingly awful example of this in my

These smells indicate something in your electrical system is getting too hot (from being grounded out, too much current, or who knows) and wires are melting insulation. You should probably open your windows and pull over.

Vinegary, Fishy Type-Smells

If you smell something that’s vaguely fishy or perhaps a bit like vinegar, chances are it’s brake fluid. If you’re smelling brake fluid, that’s bad, as that means it’s leaking from somewhere — a brake line or the master cylinder — or somewhere.

Brake fluid has a pretty distinctive scent, so it’s usually pretty easy to identify.

Also, our own David Tracy told me he thinks coolant can have a fishy smell sometimes, too. I think brake fluid is more vinegary, if that helps distinguish.

Burning Smells

Humans are very good at identifying when things are burning, but actually identifying what is burning can be trickier, which is why I’m incorporating “burning smells” as one big category.

In this category, there are a few common causes:

Clutch

Clutches and brake pads emit burning odors that smell pretty similar, because they’re both similar causes: some sort of friction material rubbing against steel. A burning clutch smells like an acrid sort of burning, and if you’re uncertain if it’s clutch or brake, maybe just take a sniff right at the wheels and see if it’s stronger there?

Some people think burned clutch smells more like burning paper, too.

Brakes

I think generally burning brake smells can be a bit stronger than clutch smells, especially if the windows are open or outside of the car, because the source is more exposed to the outside air than the clutch, trapped all cozily between the transmission and engine.

Actually Burning Stuff

If there’s actually stuff on fire in the engine, you’re likely smelling a lot of burning smells, all at once. I’m guessing this one will be pretty obvious.

Strangely Sweet Smells

There’s a couple things that can have a sort of sickly sweet smell: coolant can smell sweet, and also have a sort of humid, damp quality about it as well. A very syrupy smell, usually noticed right after the car is turned off, usually indicates a coolant leak.

Automatic transmission fluid can also smell sweet, maybe even tart, like a Sweet Tart, a little. It can take on a burnt smell if it’s overheating, too. I’ve also heard it said that overheated ATF smells like burnt toast, but people also say that’s something you smell when having a stroke, so be careful.

Power steering fluid (which is often actually ATF) can also have a sort of burnt smell, sort of sweet and burnt like a toasted marshmallow, when overheating.

Fuel Smells

I think we all know what fuel (gasoline or diesel) smells like, so if that’s what you’re smelling that’s likely what you’re leaking. The strength of this smell is usually good enough to help you localize the source, at least generally. Is it coming from the tank area or by some leaky carbs or injectors? Sniff around, bloodhound-like, and you can find out.

Exhaust Smells/Rotten Egg Smell

Your car’s exhaust has a distinct baseline odor, and if that changes it can be a big factor in letting you know what’s happening in your engine. A smell of fuel in the exhaust can indicate you’re running rich and wasting gas. A strong sulfur/rotten egg smell can mean that your catalytic converter is having trouble, which will likely be accompanied by smells of panic-farts, since those things are not cheap.

Rubber Smells

Burning rubber has a distinct odor I think (hope) most of us are familiar with. The most common source of this is of course tires, and if you’ve just been doing donuts or peeling out from stoplights, you likely know why you’re smelling that.

If the rubber smell is more subtle or evasive, there could be melting rubber hoses or bushings or belts under the hood, or possibly related to an electrical issue and burning wire insulation. A slipping belt could also be getting hot enough to emit burning-rubber smells, too.

Oily Smells

Oil has its own particular odor, and it’s different if it’s burning or just leaking. A more mild oily smell is likely a leak, while burning oil is much more nose-punching one and harder to ignore.

If you smell hot or burning oil, it’s usually strong enough that you should be able to localize the source. Is this just valve-cover-area spillage, or an actual leak from the oil pan?

Musty Smells

Time to drive that car more! Also, things may be getting damp in there. Air that puppy out.

This sort of musty, perhaps even a locker-roomish sort of smell could also indicate that the evaporator in the HVAC system may have some mildew or mold growing in it, or could be a good sign to swap out your car’s cabin air filter, if you have one.

Animal Waste Smells

I hate to break it to you, but some rats or mice or maybe squirrels have made a home somewhere in your car. Time to do a deep clean, and pull up carpet and get under and inside everything. Trust me, it’ll be worth it.

Human Waste Smells

Maybe time to make sure you’re locking your car when you leave it. Also, do you have any enemies?

Ozone Smell

This one is subtle, but some people can smell ozone gas that electrical equipment can generate, especially if something is sparking or arcing. Sometimes you can smell this around spark plug wires with compromised insulation that’s arcing against nearby metal.

Rubbing Alcohol/Window Cleaner Smell

As you likely guessed, this is washer fluid. Check to see if the plastic reservoir is cracked!

It’s likely there are even more smells that help with knowing the state of your car, but I think these are the most common. I huffed a lot of fluids to try and figure out how to describe these things, and now my head feels like a feral anvil slept on it. But if this helps you appreciate and understand the rich and varied smellscape of your car, it’s all worth it.