(Updated on October 20, 2022)
Few things ruin the interior of a car faster than water leaks. Water on the inside of your car can cause foul smells from mold and mildew. In extreme cases, the mold growth can be harmful to your health.
If you have water leaking into your cabin, don’t wait to address the issue. Here are some common sources of interior water leaks.
Sources of Interior Water Leaks
If you have a soft top convertible, you know how hard it can be to keep water out of the car. Water often leaks past the windows into the cabin, or through the seal where the top meets the windshield support (at the top of the A pillar).
Most convertibles offer several adjustments that allow the soft top to seal tightly against the windows and the A pillar. If your top doesn’t quite fit right, it might just need a simple adjustment. Soft tops with holes in them may need to be patched or replaced.
The adjustment procedure will be different on each car. For instance, early Mazda MX-5 Miatas let you adjust the soft top latches and the window height.
2) T-Tops, Removable Hard Tops, and Targa Tops
Similar to convertible soft tops, T-tops, removable hard tops, and Targa tops all have weather seals around the removable top. Over time, these seals can go bad.
When transferring a top from one car to another, you may need to make slight adjustments to the latch tension to keep the top firmly attached to the car. Sometimes replacement of the weather stripping is necessary.
3) Pressure Washing Past Seals
Pressure washing is an excellent way to detail a car, provided you’re using the pressure washer properly. If you use the pressure washer too close to the window seals or weather stripping, or you hold the pressure washer in place for too long, you may force some water into the interior.
If you’ve accidentally introduced water into the cabin, run the air conditioner for a while. This dries out the air and helps remove the excess water before it becomes a problem.
4) Sunroof Seals
Sunroofs and moonroofs have the unfortunate job of blocking out rain, while being directly exposed to the worst weather 100% of the time.
Since sunroofs sit on top of the car, water has to drain through rain rails. If these rails clog, you may notice water accumulate inside the car, particularly in the headliner.
Although they make special tools to unclog sunroof drains, you may be able to unclog them yourself using a long piece of weed wacker line and some air from an air compressor.
5) Automatic Car Washes
Automatic car washes are convenient, but they aren’t particularly great for the car. Some touchless car washes spray water at the car under very high pressure.
After you run through an automatic car wash, you may notice a little water has seeped into the cabin. After verifying that none of the windows were cracked, you may just want to run the air conditioner for a while to dry out the parts that got wet.
If you don’t notice any leaks until you’ve gone through a car wash, this is probably no cause for concern and not something that needs to be addressed.
6) Air Conditioning Drain
When you run the air conditioner, condensation builds up on the unit as it cools. This condensation needs a place to drain out of the car. Typically, you will notice a bit of water pool underneath the car after running the A/C.
When this drain gets clogged, the condensation may have nowhere to go but inside the car. You might be able to unclog the drain by locating the drain underneath the car. Some vehicles will need to be lifted off the ground to give you enough clearance to do this.
7) Door Weather Stripping and Vapor Barrier
The weather stripping on your doors serves two purposes: to eliminate noise, vibration, and harshness (NVH) and to seal out water. This rubber lining is very similar to what you’d find on the sunroof, hatchback lift gate, or convertible top seals.
Doors also contain a vapor barrier underneath the door cards. This sheet of plastic keeps the door card from getting wet. The vapor barrier is adhered to the door using a black tacky substance that sticks to everything (seriously, don’t get it in your hair).
Vapor barriers are commonly peeled back during aftermarket stereo installations, weakening the adhesion between the barrier and the door. If you have a leak in your vapor barrier, you may want to pull the door card and check to make sure that you still have a vapor barrier and it is properly installed.
8) Windshield Molding
Windshields need to be both airtight and watertight. Windshields are sealed in place using a combination of a windshield gasket and an adhesive that holds them in place.
When this seal starts to fail, you may notice water on the dashboard or condensation around the edges of the windshield. You may also hear a whistling sound that gets louder when you drive faster, as air leaks past the seal.
9) Flying Water Bottles
This might sound silly, but before you spend a lot of time or money hunting for a problem, check to make sure you don’t have any liquid containers in the car that may have leaked. As you drive around, it’s pretty easy for a water bottle to leak as it’s jostled by bumps in the road.
There are many causes of water leaks in a cabin, but you can usually tell where the leak is coming from. You will usually feel more moisture next to the source of the leak. Many of these leaks are commonly repaired at home, and this is often something you can do yourself fairly inexpensively.