When all is well, a car is a smooth-running machine. But as soon as you start hearing unexpected noises or smelling unwanted scents, you should pay attention –– because that’s your car sending you a warning of what is to come.
“Our cars have gotten very good at kind of self-adjusting for problems, which means we don’t always know right off the bat when there’s something wrong. ... But that means that by the time you’re smelling something or hearing something ... or you’re seeing drips on the driveway, it’s already gotten bad,” said Bogi Lateiner, a Phoenix-based master automotive technician and the owner of Girl Gang Garage, a network that provides hands-on training for women in the trades.
“Please don’t ignore those things. Those things are your car trying to talk to you and saying, ‘Hey, Mom, Dad, I’m not healthy. I don’t feel well,’” Lateiner said.
Here are the most common smells and sounds car mechanics say we should never ignore:
1. Burning Oil Smells
Burning oil smells have an industrial “factory kind of smell,” and they can result in a number of different potential risks, Lateiner said.
If you’re smelling this inside the cab or under your car’s hood, it likely means you’ve got oil leaking out of something like your engine or power steering and and then leaking onto something hot, Lateiner said.
Oil leaks are bad for two main reasons. For one, it means oil, which is the lifeblood of your car, is “not in the thing that it’s supposed to be in” and is not “keeping it lubricated, keeping it from getting damaged,” Lateiner explained. And it also likely means “that oil was leaking out onto something hot and burning off, making that smell that you’re smelling. If it gets bad enough, it can actually cause a fire.”
“That’s definitely a risk that you take when you let it go for too long. A little bit is probably not going to cause a fire, but a lot of it could,” Lateiner said.
There can also be visible signs of an oil leak. Noticing what color the leak is can help your mechanic diagnose the problem. If the substance is reddish, for example, the oil leak likely is coming from your power steering system or transmission system, while engine oil is generally a brown color, Lateiner said.
2. Burning Rubber Smells
Chad Cantrell, a mechanic at Forest Brook Automotive in Lynchburg, Virginia, said you might smell this when there are brake caliper issues. Brake calipers are a hydraulic clamping mechanism that squeeze the brake pads against the rotors to slow your car down when you hit the brake pedal. So when they are failing, Cantrell said, they might lock up, which in turn could be locking your wheel up and causing your tire to grab on to the asphalt because it’s not turning properly.
“That’s probably something you need to take the car in for the shop for because you’re going to tear up your tire and the car is not going to be driving very straight,” he said.
3. Sickly Sweet Smells
A common complaint clients bring their car in for is a “sickeningly sweet, acidic” or “hot syrup smell” that they are smelling in the vents or outside their car, Lateiner said.
It generally means that your coolant ― which keeps your car running at ideal temperatures ― is leaking and getting onto something that is hot. Coolant is not flammable, so you do not have the risk of fire, but you will have an expensive bill the longer you put off this repair.
If you run out of coolant, your engine will overheat, and repairing that “can cost thousands and thousands of dollars to fix,” Lateiner said.
So go to your car shop sooner rather than later if you smell this. “A coolant leak is relatively inexpensive to fix. But the effects of ignoring it are generally very expensive,” Lateiner said.
4. Burning Plastic Smells
A burning plastic smell could simply mean that you drove over a plastic bag and it has gotten caught in your exhaust, which is not a big deal because you can ignore it and let it burn off, Lateiner said.
Or it could mean a cable or a wire has come loose and is touching your exhaust, for example. You do not want to neglect an electrical issue, which is why you should bring the car in ASAP for inspection, just in case.
“It could be a totally unimportant thing like a burnt plastic bag, or it could be something more significant because it’s electrical,” Lateiner said.
5. Moldy Smells
If you smell a “dirty sock” odor in your car, that is most likely coming from your cabin filter due to mildew in your A/C box underneath your dashboard, Lateiner said. She noted that cabin filters get “really gross, especially if you’re in a humid climate.”
A quick car lesson: Often located behind your glovebox, a cabin filter is the filter for the air that you breathe inside the cabin of your car, while your air filter is for your engine and prevents dirt and debris from reaching it.
“A lot of folks don’t even know they have cabin filters. And so they tend not to do anything about them until it gets really stinky,” Lateiner said. The good news is that cabin filters are usually “very easy to replace.”
6. Rotten Egg Smells
If you’re smelling this sulfur odor out of your exhaust, it is a sign that you have a bad or aging catalytic converter, which is usually between your engine and muffler and is responsible for cleaning your car’s exhaust system. Lateiner said this smell will typically be accompanied by other alarm bells like a “check engine” light or a rougher acceleration.
It could also mean your catalytic converter just got stolen. The honeycomb-like structure contains rare metals that thieves target. More than 64,000 catalytic converter thefts occurred in 2022, most often in California and Texas, according to the National Insurance Crime Bureau.
So if “your car was fine the night before and you get into your car [the next day], and it sounds like a monster truck ... somebody cut a hole in your exhaust and cut your catalytic converter out,” Lateiner said.
7. Brake Noises
Because brakes are essential to stopping or starting your car, they should never be ignored. Some squeals or chirps can be an easy fix and are not hazards.
Lateiner gave the example of a high-pitched brake sound that you only hear when you stop your car in the morning: “You might be just dealing with a little bit of surface rust on your rotors,” which are large metal discs that are inside of each wheel and help your car safely stop when you press the brake pedal. But some might be a bigger hazard if left ignored.
“If you hear like a machine gun ‘pa-pa-pa’ kind of sound when turning, that could be a CV axle that’s going bad and that could leave you stranded if it gets worse,” Lateiner said. A constant velocity axle transfers power to your car’s wheels and keeps it moving forward while you turn.
And a grinding noise from your brakes is the “worst” noise to hear, because it likely means your problem has gotten worse and “metal-to-metal does not stop your car very well,” Lateiner said.
If you keep ignoring a grinding brake noise, you will eventually “lose all brake and your pedal will go straight to the floor,” Cantrell cautioned.
8. Clunking Noises
Clunking noises could be due to your bushings, ball joint or sway bar going bad, Cantrell said. Bushings are cushions that absorb car vibrations and noises, while a car’s flexible ball-and-socket joints help your suspension move up and down as your car travels over bumps. Sway bars are U-shaped stabilizers that keep your car level over fast corners. In short: These are are all vital car parts for keeping your vehicle moving forward smoothly.
“Older cars will start making clunks and snaps and pops and creaks and groans just like our bodies do. And it’s generally because one of the joints, one of the bushings or one of the things [where] its job is to allow movement, but not too much movement, has gotten worn and is allowing the wrong kind of movement,” Lateiner explained.
Ignore these clunks at your own peril. Cantrell shared the example of cars that have been brought to his shop with broken ball joints “and the whole car will fall like ... the fender will be on top of the tire.”
9. Rattling Noises
Cantrell said rattling noises could be a small problem like an “exhaust plate or a bracket that has gotten loose and is now rattling, but they could also be a larger issue like a timing chain tensioner problem.”
Timing belts and timing chains keep your engine synchronizing properly, so that your car’s pistons and valves operate correctly. So when these car parts “go bad, it can lock up your engine,” he said
“If you’re hearing that noise in the engine department, you probably need to get a mechanic to inspect whether you need a [new] timing belt or timing chain,” Cantrell said.
How to help your mechanic diagnose what’s wrong
You may not be able to speak car like a mechanic, but if you drive your vehicle regularly, you know it better than anybody else, and you should listen to your intuition that is telling you something is not right.
When you bring your car to be repaired, go beyond saying something sounds or smells “funny,” and be as specific as you can about when and where you are hearing or smelling what is concerning you. Share when and where you hear the screech or weird smell.
“Note when it’s doing it, what speed you’re going,” Cantrell said about unwanted noises. He said it can help narrow down the issue if you hear it on a hill, for example.
“If you can record the sound and play it for us and make the noise for us ... it really does help us figure out what it is,” Lateiner suggested. “It saves time, which translates to saving you money the more you can point us in the right direction.”