Unusual smells in your car aren’t just unpleasant—they’re warning signs. From musty air-con funk to the dreaded burnt rubber stench, here’s how to decode common car odours, what they mean for your vehicle’s health, and if it’s time to head to the workshop.

Your car is more than a machine: it’s a finely tuned system. And just like the human body, it can give off subtle (and not-so-subtle) cues when something’s wrong. In Singapore’s humid and hot climate, odours can become more pronounced, and with cars often parked in tight HDB or condo lots, you might notice smells sooner rather than later.

Ignoring strange car odours and the root problem isn’t just unpleasant, it could lead to expensive repairs, safety issues, or health hazards. Here’s a guide to the most common car smells and what they could be trying to tell you.

Musty or Mouldy Smell (Like Damp Clothes)

What it likely means: A build-up of mould, mildew, or bacteria in the air conditioning system.

Cause: Clogged aircon filters, dirty evaporator coils, or moisture trapped in the ventilation system.

What to do:

• Replace the cabin air filter. This should be done every 10,000 to 15,000 km in Singapore’s climate.
• Have the air conditioning system cleaned professionally. Many workshops offer antibacterial or ozone treatments.
• Consider running the fan without AC for a few minutes before switching off the engine to reduce moisture.

How to prevent it:

• Change your air filter every 10,000–15,000 km.
• Occasionally, run the fan mode to dry out moisture.
• Avoid setting the AC to very cold unless needed; this reduces condensation buildup.
• Humid air encourages mould growth. Get your aircon serviced regularly, especially if you park in basement lots or rarely use the fan mode.

Burning Rubber

What it likely means: A loose or slipping belt or rubber hoses coming into contact with hot engine components. The heat from long idling in traffic jams or tight parking garages can exacerbate these smells, especially in older cars.

Cause: Overheated belts, misaligned pulleys, or damaged wiring insulation.

What to do:

• Stop and inspect the engine bay only when the car is cool and safe to do so.
• Get the belts and hoses checked at a trusted mechanic, especially serpentine or drive belts.

How to prevent it:

• Have your belts inspected at every oil change.
• Avoid aggressive acceleration, especially when the engine is cold.
• Don’t delay replacing old or squeaky belts. 

Sweet Syrupy Smell

What it likely means: A coolant or antifreeze leak. Coolant is a bright-coloured fluid (typically green, yellow, or orange) that keeps your engine from overheating. It has a distinctively sweet smell because it contains ethylene glycol, a chemical compound that’s toxic but sweet-tasting (to animals and humans).In Singapore’s stop-start traffic, engine cooling systems work overtime. Keeping them in good condition is vital to avoid overheating.

Cause: Damaged radiator, leaking hoses, or a failing water pump.

What to do:

• Check for green or orange fluid under the car.
• Don’t ignore it. Coolant leaks can cause engine overheating.
• Visit a mechanic promptly to prevent expensive repairs.

How to prevent it:

• Flush and replace coolant according to your service schedule.
• Check coolant levels monthly.
• Inspect hoses for cracks, especially before long road trips.

Rotten Egg (Sulphur-Like Odour)

• What it likely means: A problem with the catalytic converter or fuel system. This smell is usually caused by a malfunctioning catalytic converter, a component in your exhaust system that converts harmful gases into less toxic emissions. Specifically, it means the converter is failing to properly process hydrogen sulfide, a byproduct of burning fuel. It can also indicate that your engine is running “rich,” meaning too much fuel and not enough air are entering the combustion chamber. This creates excess unburnt fuel, which overwhelms the converter and causes that rotten egg smell.
• Emission control is tightly regulated, so don’t risk a failed inspection or environmental fine.

Cause: The converter isn’t processing hydrogen sulfide in the exhaust properly, or the engine is running rich aka too much fuel.

What to do:

• Get your emissions system checked immediately.
• It could be a sign of a failing catalytic converter, which is costly if left unaddressed.

How to prevent it:

• Use high-quality petrol from trusted stations.
• Follow regular service intervals to keep your fuel system clean.
• Address check engine lights promptly.

 Gasoline Smell Inside the Car

What it likely means: A fuel leak or evaporation system issue.

Cause: Leaking fuel injectors, fuel lines, or a faulty fuel cap.

What to do:

• Check if you recently refuelled. Spills can cause lingering smells.
• If persistent, visit a workshop, as it could pose a fire risk.
• Avoid driving if the smell is strong. It’s a potential safety hazard.

How to prevent it:

• Never overfill your petrol tank.
• Replace damaged or loose fuel caps immediately.
• Regularly inspect under the car for leaks.

Burnt Oil Smell

What it likely means: Oil leaking onto hot engine parts. Frequent short-distance driving can mask oil loss until it’s too late. Regular checks are crucial.

Cause: Valve cover gasket leak or oil spilt during an oil change.

What to do:

• Look for oil stains under the car.
• Monitor oil levels. Low oil can damage your engine.
• Book a service visit quickly.

How to prevent it:

• Schedule regular oil changes.
• Always check for leaks after service visits.
• Watch for smoke or oily residue under the bonnet.

Melted Plastic or Electrical Burning

What it likely means: Electrical short or overheating wiring.

Cause: Damaged insulation, faulty wiring, or a malfunctioning component like the alternator.

What to do:

• Stop driving immediately and turn off the car engine. Disconnect the battery if you know how to.
• Do not attempt DIY fixes. Seek immediate professional help.
• This smell can precede electrical fires. Do not delay seeking immediate and professional help.

How to prevent it:

• Avoid DIY wiring jobs or unauthorised installations.
• Have your car’s battery and electrical system checked annually.
• Watch for flickering lights or failing electronics.

Exhaust Fumes Inside the Car

What it likely means: A serious exhaust system leak. In Singapore’s often bumper-to-bumper driving conditions, good air circulation in your car is crucial.

Cause: Cracks in the exhaust manifold, worn seals, or poor ventilation.

What to do:

• Open windows immediately.
• Visit a workshop. Carbon monoxide poisoning is a real danger.

How to prevent it:

• Ensure exhaust servicing is done by reputable workshops.
• Pay attention to exhaust noise or performance issues.
• Install a carbon monoxide detector in your car if you often idle for long periods.

Don’t Ignore the Nose

A strange smell in your car isn’t just unpleasant, it’s your vehicle’s way of telling you something’s wrong. Whether it’s a sign of a minor issue or a more serious fault, the key is to act early. This not only protects your wallet but also your health and safety, especially in Singapore’s dense traffic and hot climate.

If the problem seems manageable and the car is still safe to drive, head to a trusted mechanic or workshop for a thorough check. But if the smell is strong, persistent, or you suspect a fuel leak, electrical fault, or exhaust issue, it’s best to stay put and call for help.

Need fast help in Singapore? Automobile Association of Singapore (AAS) offers 24/7 roadside assistance. Call 6748 9911 or visit aas.com.sg/immediate-assistance for support you can rely on.

Don’t ignore what your nose is telling you, your safety could depend on it.