Why Does My Car Smell Musty in Winter? How to Find the Source and Fix It

The short answer: a musty car smell usually means something is staying damp. The usual suspects are wet carpet from melted snow, water sitting in the heating and A/C system, a dirty cabin air filter, or a leak. Find the moisture and dry it out. An air freshener only covers it up.

Here's how to track it down, and which smells aren't a cleaning problem at all.

Why does my car smell musty in winter?

Snow melts off boots into the mats and carpet, the windows stay shut, and the damp has nowhere to go, so the smell builds.

Consumer Reports lists snow tracked in on shoes among the ways moisture ends up in the footwell. Health Canada's guide to moisture and mould is written for homes, but the lesson carries over: mould can start growing within 48 hours where there's too much moisture, and a musty or earthy odour is one of the signs to look for.

How do you find where a musty smell is coming from?

Notice when the smell appears, then check the vents, the carpet under the mats, the headliner and the trunk, one at a time.

Consumer Reports recommends this process of elimination, and names water leaks, blocked A/C drains and old cabin air filters as common causes. Rule out food or a spill under a seat, then go through this list:

• Only when the fan is on? Start with the heating and A/C system (next section).
• All the time, and strongest near the floor? Lift the mats and press a dry paper towel into the carpet. If it comes up damp, you've found your source.
• Damp spots on the headliner or seats? Consumer Reports says clogged sunroof drains can send water there.
• Smell at the back of the car? Check the trunk. Water can seep in past the seals.
• Wet carpet, but no snow to blame? Capital One's car guide lists blocked drains, worn door, windshield, sunroof or trunk seals, and a bad heater core. Fix the cause, or the carpet will just get wet again.

Why does my car smell musty when the heat is on?

Water left in the A/C evaporator, or a dirty cabin air filter, can smell musty as soon as the fan pushes air through.

Consumer Reports explains that condensation from the evaporator normally drains out under the car, but some can stay behind, and bacteria and mould can form. AAA says the cause can be as simple as a dirty cabin air filter.

Try these in order:

1. Check the cabin air filter. It's often behind the glove box. AAA suggests replacing it every two years or 24,000 miles (about 38,600 km), or sooner if anyone smokes in the car. Your owner's manual has your car's schedule. 2. Disinfect the system. Consumer Reports' method: remove the cabin filter, open the windows and set the fan to low. Then spray an A/C disinfectant from an auto parts store into the air intake at the base of the windshield. Follow the label and work outdoors. 3. Dry the system before you park. Consumer Reports suggests turning the A/C off and letting the fan run for a few minutes before you shut the car off.

If a clean filter doesn't help, AAA says to have a mechanic check for water. Consumer Reports says a blocked A/C drain is a mechanic's job too.

How do you dry wet car carpet in winter?

Bring the mats inside, blot the carpet with dry towels, then run the heat with recirculation off and let the damp air out.

Try to get it done within a day or two, given that 48-hour window for mould:

• Dry the mats indoors, then press dry towels into the wet carpet until they stop picking up water.
• Drive with the heat on and recirculation off. Our post on why car windows fog up in winter explains why recirculation holds moisture in the cabin.
• Open the doors on a mild, dry day, or in a garage with the engine off. Health Canada says not to idle a vehicle in a garage, even with the door open.
• Switch to rubber all-weather mats. Consumer Reports says to take the carpeted mats out rather than stacking liners on top of them.

Our guide to cleaning your car's interior at home covers how to clean fabric without soaking it.

Do air fresheners or ozone get rid of a musty smell?

Air fresheners and odour bombs mostly cover a smell. Ozone can help with lingering odours, but it won't dry wet carpet or stop a leak.

Consumer Reports says odour bombs often just mask the problem. It also says ozone machines can work well on lingering smells, but ozone can harm your lungs and worsen breathing problems. Never run one with people or pets in the space.

Is a musty smell in a car bad for your health?

It can be if mould is growing, especially for children, seniors, pregnant people and anyone with asthma, so don't just live with it.

Health Canada's guide links mould exposure at home to eye, nose and throat irritation, coughing, wheezing and shortness of breath. It also says it can worsen asthma. That guide is about homes, so treat this as a reason to act, not a diagnosis.

If you can see mould spreading, a shampoo may not be enough. Health Canada says mouldy carpet and underpad in a home should be cut out and thrown away, and Consumer Reports warns that fixing water damage can mean removing interior panels.

Which car smells mean you should see a mechanic, not a detailer?

Sweet, gasoline, rotten-egg and exhaust smells point to a mechanical problem. They aren't cleaning jobs, so get them checked before you book a detail.

• Sweet or fishy smell from the vents: this may be a bad heater core leaking coolant. Consumer Reports says to get it fixed right away. If the temperature gauge is rising, pull over and let the engine cool, says AAA.
• Gasoline: AAA says this can be a fuel leak, a faulty gas cap or another fuel system problem.
• Rotten eggs: AAA points to the exhaust system, including the catalytic converter.
• Exhaust inside the cabin: treat this one as urgent. Vehicle exhaust contains carbon monoxide, and Health Canada says it has no smell, taste or colour. Early symptoms include tiredness, headaches, flu-like symptoms and shortness of breath. Stop somewhere safe, get everyone into fresh air, and have the car checked before driving it again. If anyone feels unwell, call 911.

Can a detailer remove a musty smell from a car?

Often, yes, if the source is in the carpet or fabric and the water problem is already fixed. Cleaning alone can't stop a leak.

Our Deep Interior Clean starts at $120 and includes hot-water shampoo extraction, salt stain and spill treatment, and odour neutralization. For smells that linger, Ozone Odour Treatment is a +$40 add-on. You can compare everything on our services page.

We'll be upfront about the limits. Leaks, blocked drains and carpet replacement are jobs for a mechanic or body shop, and they need sorting first. We also can't promise that every smell will go.

Polish & Go is a mobile detailing service based in Milton, also serving Campbellville, Oakville, Georgetown, Halton Hills, Burlington, Mississauga and Brampton. Confirm water and power access when you book. You can book online or call 519-835-5580.