· by Michael Blair, Nashville's Mobile Detailing
October in Middle Tennessee means cars parked in driveways and on streets under trees, collecting leaves overnight and rain every few days: a normal October at the airport has about eight days with measurable rain, according to NOAA’s 1991–2020 climate normals for Nashville International Airport, and 3.36 inches in all on the National Weather Service’s Nashville climate page. Most of what lands on a car blows off on the next drive. On a fall detail we go looking for what stays: leaves stuck wet to the paint, leaves packed into the channel below the windshield, and debris washed into sunroof drains most owners never think about until there is water inside the car.
Leaf stains on the paint
We have not seen a carmaker put a number on how long a wet leaf can sit on clear coat before it marks it, and we would be wary of anyone who quoted one. The nearest thing in an owner’s manual is about something else that falls from trees: Kia’s manual on keeping paint in good condition calls bird droppings highly corrosive, says they may damage painted surfaces in just a few hours, and says to remove them as soon as possible. A car parked under a branch all fall collects both, so we treat a leaf stuck to the hood the same way and get it off this week.
If a leaf has left its outline behind, we start with a wash and the mildest product that lifts it, and go to machine polishing only after a test section on one panel shows the mark needs it. Our exterior detail finishes with a machine-applied sealant, so whatever lands next sits on that layer. Sweetgums add their own mess: UT Extension’s guide to trees to reconsider before planting says their seed capsules, the sweetgum balls, can create a nuisance, and on a car they are one more thing we pick out of the gaps around the wipers.
What is the cowl under the windshield?
Lift the wipers on most cars and you find a plastic panel with slots in it, sitting over a channel that takes the water running off the windshield. That channel is the cowl. Leaves slide down the glass and settle there, and on many of the cars we work on, the fresh air the heater pulls in comes from that same corner. A cowl full of wet leaves is not something we leave for the owner to find in January.
Clearing it means lifting the wipers, taking the debris out of the channel by hand or with a vacuum, and on some cars removing the panel itself. We do it on every fall visit. If a carpet is already damp by the time we get there, finding where the water came in and drying it all the way through are covered in our post on interior detailing in a humid climate.
How do sunroof drains work?
A sunroof sits in a frame built to catch water and drain it away through tubes, two or four depending on the car. In Subaru’s service bulletin on sunroof leaks in 2010–2013 Legacy and Outback models, water poured into the front corners of the frame should flow freely and leave the car at the base of the pillar beside the windshield; when a drain tube is kinked or restricted, the water collecting in the frame overflows and leaks into the interior, in that case around the map light. Genesis issued a bulletin in January 2026 for GV70 and GV80 sunroof drain hose plugs clogged with foreign material, and it lists a gurgling noise from the sunroof while driving in the rain among the signs.
Neither bulletin names leaves, and Subaru’s also blames tubes kinked where they bend down the pillar. On a car that parks under trees, though, leaf bits and needles in the frame are what we clear first. We test each drain with water poured slowly into its corner and keep any air pressure low, the way Subaru tells its own technicians to use compressed air carefully. A drain that will not clear, or a tube that turns out to be kinked, goes to a shop or the dealer to have the hose replaced, and it is worth asking the dealer whether your model has a bulletin or campaign like the Genesis one. Signs a drain is backing up:
- A damp or stained headliner near the front of the roof
- Water inside the car after rain with no other obvious leak
- A gurgling sound from the sunroof when driving in the rain
- Water that pools in a corner of the frame instead of running away
What does the cabin air filter do?
The cabin air filter cleans the outside air the heating and air conditioning pull in. Kia’s owner’s manual page on the climate control air filter says that as dust and other pollutants build up in it, airflow from the vents can drop and moisture can collect on the inside of the windshield. Kia’s schedule is every 15,000 miles or once a year, with more frequent changes on dusty or rough roads. Where the filter sits varies from car to car, and your own manual shows it.
On a car that spends the fall under trees, we suggest making that yearly change in October, before the heat runs every morning. If the cabin still smells sour after a new filter, we pull back the mats and feel the carpet before reaching for anything scented. A wet floor calls for extraction and drying in an interior detail, and for checking the cowl and the sunroof drains above it so it does not happen again. If you would like all of it looked at in one visit, ask us for a quote.
Sources
- NOAA National Centers for Environmental Information, U.S. Monthly Climate Normals 1991–2020, Nashville International Airport (USW00013897) — October normal of 3.36 inches, with 8.4 days of at least 0.01 inch of rain.
- National Weather Service Nashville, Nashville climate page — October normal precipitation of 3.36 inches at Nashville.
- UT Extension, SP512 Trees to Reconsider Before Planting (1998) — Sweetgum seed capsules (sweetgum balls) can create a nuisance.
- Kia, 2023 owner’s manual, Keep paint and trim in good condition — Bird droppings are highly corrosive, may damage painted surfaces in a few hours, and should be removed as soon as possible.
- Subaru of America, Service Bulletin 12-117-10R, Water Leak from the Map Light Area (revised 2016) — Kinked or restricted drain tubes let water in the sunroof frame overflow into the interior; water test each drain; careful compressed air; replace a kinked or uncleared hose; retest after repairs.
- Genesis Motor America, Technical Service Bulletin Campaign 26-01-006G, Water Leak from Clogged Sunroof Drain Hose (2026) — GV70 and GV80 drain hose plugs clogged with foreign material; water leaks inside; gurgling noise from the sunroof in the rain.
- Kia, 2023 owner’s manual, Climate control air filter — The filter cleans outside air entering through the heating and air conditioning; a clogged one reduces airflow and can fog the windshield; replace every 15,000 miles or once a year, sooner on dusty roads.
FAQ
Fall Leaves, Clogged Drains and Stained Paint — questions
Can leaf stains be removed from car paint?
It depends on how far the mark has gone into the clear coat. We start with a wash and the mildest product that lifts it, and machine polish a panel only after a test section shows it needs that. Taking leaves and bird droppings off the paint soon is easier than any of it.
How do I know if my sunroof drains are clogged?
Water inside the car after rain, a damp headliner near the front of the roof, or a gurgling sound from the sunroof while driving in the rain are the signs carmakers describe. To test, open the sunroof and carefully pour a little water into each corner of the frame. It should run away freely and out of the car; if it pools, the drain is blocked or the tube is kinked.
Why does my car smell musty when I turn on the heater?
We start with the cabin air filter, since every bit of outside air the heater pulls in passes through it, and with clearing leaves from the channel below the windshield. If the smell stays after a new filter, we check the carpet and padding for water, which on a car parked under trees can come from a blocked sunroof drain.
How often should a cabin air filter be changed?
Kia’s schedule is every 15,000 miles or once a year, and sooner on dusty or rough roads; your own manual gives your car’s interval and where the filter sits. A clogged filter cuts airflow from the vents and can let moisture fog the windshield. On a car parked under trees all fall, we suggest October.