Left Your Car Windows Open In the Rain? Here’s How to Quickly Dry It Out

It’s easy to forget to roll up your car windows on a beautiful summer day, but nice summer days have a way of turning into rainy days in a matter of minutes. Here’s how to dry your car out if your day got a little damper than expected.

Failing to get out to your car fast enough when the rain comes doesn’t mean a damp drive home, it can also mean a musty smelling car, mildew, and worse. Let’s take a look at how to get the water out before it becomes a problem.

Remove the Excess Water

Whether your seats are just damp or you have standing water in the car, start by getting as much out as possible. A wet/dry vacuum will make short work of the standing water. For maneuverability in the vehicle, a small 2.5-gallon model is handy, but if you have a full-size model it will work just as well—especially if you use a long hose. If you’re looking for an excuse to buy a 20-foot hose for your shop vac, we can assure you it’s great for car detailing without lugging the whole shop vac around.

When vacuuming be sure to work in a consistent pattern across the seats and floors, try to make a grid pattern in one direction and then in the opposite direction so you maximize the amount of water you extract while minimizing the risk of missing a spot.

Once you’ve dealt with standing water, use some towels to soak up more water. Push down on them into your seat to absorb as much water as possible.

Removing the water immediately is best (and much faster than the additional ways we’re about to dig into). Whenever possible, shop vac and blot up all the water you can before proceeding.

If you don’t have a shop vac and don’t know anyone you can borrow one from, consider calling local auto-detailing shops to enlist professional help. They have the equipment on hand to deep clean upholstery and carpet with water (and extract it!) so give them a ring.

Let the Air In

While keeping your windows open was what got you into this mess in the first place, you want to make sure your vehicle is getting ample airflow. The air will help dry things out fast.

The key to keeping air moving through your vehicle is the use of a fan. You want to have a fan that is blowing across your floors and across the seats (or whichever areas are wet). A larger high-velocity shop fan will come in handy. You’ll have to keep your doors open and let the fans do their job for 12 to 24 hours.

Keeping your vehicle in a garage during this time is ideal from a security standpoint (and to ensure another passing rainstorm doesn’t soak your car all over again), but if possible leave the garage door cracked a few inches or some windows cracked to allow humid air to escape.

If you don’t have garage access or you’re away from home, you can try cranking the heat in your car or the defroster and aiming the vents toward the seats and floorboard. This is a temporary fix, and you’ll want to get some proper ventilation going through your vehicle to dry it out thoroughly.

Using the defroster might sound counterintuitive, but it’s a smart solution that combines hot air (which can hold more moisture) and the AC system (which extracts moisture). The reason you see puddles under cars during the summer is that the AC unit is pulling moisture from the interior of the car and dumping it out.

If you don’t want to waste gas, and it’s a low-humidity day with the sun shining bright, you can let nature do the drying for you. Cars can get up to 40F higher than the outdoor temperature quite quickly. Park in the direct sunlight, roll your windows down just a bit, and the heat will help vent the damp air right out the windows.

Spot Dry

After you do the other two steps, there’s a chance you may still find some wet spots. These will usually be found on your floorboards or at the edge of your seat—spots that got really wet and aren’t drying fast as the rest of your car.

To avoid mold, you want to be sure you get all of the moisture out of your car. You can spot dry using a blow dryer. Keep the blow dryer moving while you use it and take frequent breaks. Blow dryers are not intended for extended use and will overheat if you run them for too long.

Use Desiccants

Finish up with some moisture-absorbing products. You can purchase disposable moisture absorbers that come in a plastic container. These desiccants help to keep the drying process going.  You can see the moisture they pull from your vehicle as the container fills with water.

In addition to using make-for-the-purpose desiccants, you can also use “crystal” cat litter. Grab a bag of unscented silica-based cat litter, cut open the top of the bag, and just place the entire bag sitting on a dry spot in your car (like the middle of the back seat that didn’t get soaked by the rain). The “crystal” cat litters on the market are actually just little silica crystals exactly like the silica crystals found in many much more expensive desiccant products. The silica crystals absorb moisture until they are totally saturated or the environment they are in has been reduced to around 65% humidity.

If you want you can significantly increase how effective the crystal cat litter is by pouring it into a pair of pantyhose or a very fine-mesh bag. If you cut the pantyhose into multiple segments, tying off the ends of the tubes with a firm knot, you can place the bags of desiccant all over the car. Not only does this spread out the drying power but it also increases the exposed surface area of the crystals which will speed up the drying time too.

For maximum effectiveness, leave the desiccants in your car past the point that you think it is dry enough. They will keep working until they are fully saturated and will help draw out moisture from deep inside the upholstery.

Remove Mold

You’ve taken steps to thoroughly dry out your car and prevent mold, but it could still happen. If you’re concerned, inspect your car thoroughly including your seats, seat belts, steering wheel, and fabric. If you spot bits of mold, open your car windows and doors for 15 minutes to air out spores.

Next, use a toothbrush to scrub the areas. Since vinegar is an acid, apply it over those spots and scrub. It should break down the spores. Use a wet/dry vacuum to get up any loose bits and eliminate any removing moisture from your car.

What Damage Can Happen When You Leave Car Windows Down in the Rain?

The short answer here is a lot of damage.

One of the most obvious issues that can arise is car electrical problems. As you’re probably aware, electronics and water don’t mix, and your car, well, it’s basically one big, moving electronic. When water makes its way into your car, it seeps into the dashboard, door and window controls, radio, and even the car’s overall computer system which could make them faulty.

While your car is meant to handle water during drives, allowing it to soak (regardless of it being inadvertent) can cause mechanical issues with the starter and brake. In worst-case scenarios, your car could experience hydrolock.

Hydrolock causes a car’s engine to seize and fail, and a large quantity of water invading the cylinders is the cause. You most often see it happen when people attempt to drive through large puddles, but it could happen if you leave your window down as well. Essentially, if water fills just one of the cylinders, the engine can’t compress effectively and all pistons stop working.

Regardless of whether all of the above steps seem to have your car back on its feet, or, well, wheels again, it’s still best to take it in for a full inspection with a professional to ensure you’re not overlooking damage.

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Between leveraging the power of the sun to cook the moisture out of your car and some hands-on techniques like vacuuming the water out and putting desiccants in your car to absorb moisture, you can get ahead of the mildew and dry things out before your car smells like an old basement.