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Car Care Advice

8 Reasons Your Car Smells Like Rotten Eggs (+ Removal Tips)

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If your car smells like rotten eggs, please don’t hold your breath waiting for the smell to go away by itself. It’s a sign of either serious mechanical problems or something foul-smelling that was left behind — and you shouldn’t ignore it. 

Wondering what might be causing a sulphuric or rotten egg smell in your car?

Let’s identify 8 possible reasons why your car could smell like rotten eggs, how to get rid of the rotten egg smell, and other odors that could mean trouble.  

This Article Contains: 

Let’s begin.

8 Urgent Reasons Why Your Car Smells Like Rotten Eggs

It’s normal for your car to produce emissions to function correctly. 

However, certain smells — like the uninviting aroma of rotten egg — could indicate a problem with your vehicle. It can happen whether you have a new car or old one, so it’s essential to be on the lookout and keep an eye (or a nose) open for these issues: 

1. Your Car Battery Could Be Bad

Your car battery contains sulfuric acid. Usually, the sulfuric acid stays in the battery case and doesn’t cause any problems. But if your car battery suffers any damage, the sulfuric acid can leak out, causing that rotten egg odor.

If any battery acid has leaked out of a cracked case, contact your mechanic and have them deal with it. 

Important: Avoid jump-starting a defective battery, as it could risk an explosion. 

2. You Have A Faulty Catalytic Converter

Your catalytic converter chemically scrubs your car’s exhaust of harmful pollutants before they can enter the atmosphere. When hydrogen sulfide flows through the catalytic converter, the platinum in the converter turns this toxic gas—hydrogen sulfide—into odorless sulfur dioxide (SO2). 

A faulty catalytic converter may not produce sulfur dioxide, leaving your car smelling like a rotten egg. 

Aside from the nasty car smell, a failing catalytic converter can cause poor gas mileage, problems with starting your car and acceleration, and lighting up your Check Engine Light.

In this case, your mechanic should replace your broken catalytic converter as the extra pollutants in your failing catalytic converter may trigger high temperatures that can cause a car fire.

3. Your Fuel Pressure Sensor Is Faulty

Your fuel pressure sensor regulates fuel flow within your engine. When your fuel pressure sensor fails, your car can run with a fuel mixture that’s too rich. Too much oil in your fuel mixture can leave you with a clogged catalytic converter. 

You ‘ll experience poor drivability and bad fuel usage with a faulty fuel pressure regulator, and the Check Engine Light will pop on.

4. Your Fuel Filter Is Worn Out

A worn-out fuel filter can cause an over-rich fuel condition. The too-rich fuel mixture then allows an influx of sulfur to move into the catalytic converter, burning it out. 

Note: A failing filter causes the same problem as a failing pressure sensor.

You should fix a worn-out fuel filter or faulty fuel injection system immediately. If ignored, it can cause damage and leave you with a broken catalytic converter.

5. A Bad Manual Transmission With Leaky Or Old Transmission Fluid

On older cars, manual transmissions use sulfur-based lubricants. If the lubricants drip out, they produce a rotten egg aroma. 

The smell can also be your old transmission fluid leaking and coming into contact with the hot engine. 

Do you remember the last time you flushed it? 
Because it might need changing. 

Leaking transmission fluids can also mean damaged gears, which can be a very costly repair job

You should contact your mechanic if transmission fluid is dripping beneath your car, so they can locate the leak and get it fixed.

6. Your Exhaust System Could Be Damaged

Your oxygen sensor monitors the amount of oxygen in your exhaust system. A bad oxygen sensor can cause your engine computer to direct too much fuel into your combustion chamber. The over-rich fuel will eventually lead to a clogged catalytic converter — resulting in the sulfur smell.  

Also, if your exhaust system becomes damaged or rusted, it can cause an exhaust leak and untreated exhaust fumes to escape. In addition to producing a revolting car smell, there’s also the possibility that deadly carbon monoxide from your exhaust fumes can get inside your car. 

If your exhaust sounds noticeably louder than usual, open your windows to prevent the harmful gas from concentrating and contact your mechanic immediately!

It’s best not to delay repairing a damaged exhaust system. 

7. You Could Be Storing Forgotten Food Remnants

It will be helpful to eliminate the most direct and obvious cause of the problem: rotten eggs or any leftover food. If you allow eating in your car, there might be some forgotten food remnants.  

Although this doesn’t indicate car trouble, the unpleasant smell can be overwhelming. 

If this is the case, remove the eggs or other food items, and dispose of them. The bad smell should then disappear. 

8. There Could Be A Small Dead Animal

If your car is parked outdoors, small rodents (mice, rats, and squirrels) may use your car as a safe place to live, especially if you don’t drive your car regularly. These rodents can climb into your vehicle’s under-hood area from beneath the car and nest inside your air circulation system. 

Once they’re under your hood, your car’s electrical wiring is at risk of being chewed on. 

If one dies from natural causes or gets sucked into a ventilation fan, its body decomposes, giving off sulfur compounds that smell like rotten eggs.

Ghastly right? 
Your mechanic will likely dismantle your car’s air intake and ventilation system to the point where they can remove the animal’s body and all related debris.

Now, since we’ve identified where the putrid odor could be coming from, let’s dig into ways to remove the unpleasant smell.

How To Get Rid Of The Rotten Egg Smell

To remove the smell from your car, your mechanic will need to eliminate the source — mechanical issue, food, or dead animal — that’s causing the smell. Once the relevant root cause is resolved, the sulfur smell should disappear. It’s best to catch problems early to make them less costly to fix. 

However, if the bad smell has already penetrated your car interior, why not try these helpful tips: 

A rotten egg odor is truly overpowering, but there are other smells from your car that you also need to take note of.

Other Car Smells That Could Mean Trouble

There are several other odors you might encounter from your vehicle. Some might be pleasant, like the sweet smell of ethylene in coolant fluid, but some might indicate a harmful gas leak or lead to a costly engine repair job. 

It’s essential to take note if you smell something like:

1. Gasoline

If a gas smell lingers after you fill the tank, it could mean you got some on your shoes or clothes while refueling at the gas station. 

A leak in your car’s fuel system or vent hose could also cause a gas smell. This could be an exhaust leak and a potentially dangerous issue that requires professional diagnosis and repair by your mechanic. 

2. Burning Rubber

A burning rubber smell often indicates that your car has a loose belt or worn-out rubber hose that’s now touching the hot engine. A burning smell could also signal you have a burned-out electrical fuse or worn-down brakes

If you’re experiencing a burning rubber smell, your mechanic should take a look and replace the faulty part. 

3. Sweet Syrup

A leak in your radiator or heating system can produce the sweet smell of syrup. This smell is the ethylene in your coolant, and you might notice it while the car is running or just as it’s turned off. 

This leak can cause a major system breakdown and lead to serious engine repair. You need to have it checked quickly.

4. Musty Scents

If you start smelling the unpleasant odor of old gym socks while your air conditioner is on, this is usually a sign of mildew or mold growing inside your AC. 

We recommend you turn off the air conditioning when you’re near your destination, then run the fan for a few minutes to prevent mildew build-up. It helps the water on the coils in your air conditioning unit to dry out and discourages the growth of bacteria.

Final Thoughts

Whenever you smell something suspicious while running your engine, such as rotten eggs, gasoline, smoke, or a burning smell — don’t ignore it. These are often signs that there’s a problem that needs remedying.

For professional help, make an appointment with a trusted mobile mechanic like RepairSmith if you’re having car trouble, or smell rotten eggs or any other toxic gas in your car.

RepairSmith’s online booking system makes contacting us and scheduling appointments effortless. We’re available 7 days a week, work around your schedule, and complete repairs in your driveway!