After owning your car for a while, you get used to its unique little noises. The purr of the engine, the squeak of the springs when you get behind the wheel, and all the beeps of the dash controls. Then, one day, you pull up to a stop, or you take a hard corner, and you hear a strange sloshing noise.
Your mind reels. What could possibly be sloshing around like that? Is it a problem with the radiator? Did a leak in a body panel let water in after a rain?
Most of the time, these random water sloshing sounds are caused by a clogged drain in one of the body panels, roof, or doors. Though there are a lot of different things that can cause a sloshing sound inside a car. The good news is that the most likely suspects, like the clogged door and windshield of sunroof drains, aren’t going to cause any immediate threat to the car. However, they could lead to some ugly mold and mildew problems later.
However, there are also a few other things, like a clogged AC condensate drain or a coolant system problem, that could be a much more expensive repair. So, the wise move is to put your listening ears on to try to pick up where the sound is coming from and what motions cause the sloshing sound.
The Right Tools For Cleaning Body Panel Drains
Your car has all kinds of different drains in doors and body panels. They help divert rainwater harmlessly under the car. Unfortunately, they’re usually pretty small, hard to find, and fiddly to clear. There’s no single catch-all tool for clearing them. However, it helps to arm yourself with some of the following.
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Where’s That Splash Coming From? Identifying The Location Of Water Sloshing Noise In Your Car
Water sloshing when you step hard on the brakes or roll to a stop might result from a clogged door drain, a front/hood drain, or even a sunroof drain. It’s also possible for it to be a mechanical problem like the engine coolant or heater core.
Most of the time, though, it’s a clog in one of the special ports installed in the body panels. They’re designed to let the water that gets into your doors during a heavy rain storm drain back out again. Unfortunately, they can get clogged rather easily by rust, mildew, mold, or road grime.
When you stop, the water inside roils forward. When you start out again, the acceleration force is usually lower and less sudden, so you might not hear any sloshing.
1. Water Sloshing In the Doors When Braking Hard or Stopping
Water sloshing when you stop or brake hard is often a clog one or more of the large door drains. Testing, if it’s the door drains, is as easy as opening and closing the doors. The violent shaking motion should make the water inside slosh again.
If you don’t drain the doors out, the water inside will start causing corrosion inside the bottom of the door. There’s also a real risk of mold and mildew building up inside the door.
How to Fix
Unclogging your door drains is relatively easy. However, it might take several tries to get the full volume of water to drain out, even after you get the initial clog to release.
2. Water Sloshing Sound from Your Car’s Floor
A lot of times, when you have water sloshing from the floor, it’s because a rocker panel or rail drain is clogged. You might even clear the drain on your doors, only to still hear the sloshing sound when you brake hard, as doors and rocker rails seem to like to clog at the same time.
How to Fix
Finding the tiny drain holes in the rails is tricky, as they are very tiny and low down. The best bet is that they’re right under the back corner of the front door. If you can’t spot them right away, turn to your car’s repair guide or owner’s manual. Some cars have front and rear drains on the rails.
If you’ve got rust on the rocker panels, chances are good that it will clog up the drains again. So, don’t be surprised if you have to loosen these drains up several times over the course of a few weeks.
3. Understanding and Eliminating Sloshing Water Sounds from Your Windshield
A sloshing water sound that sounds like it’s coming from the windshield or the hood of the car and not the dash is usually a clogged front drain. They’re designed to shed excess water from the windshield and front of the car. They easily get clogged by simple things like tree debris or even a nasty insect nest!
How to Fix
The front drains can be hard to access, and some models require you to pop the hood to get at them. Check the owner’s manual or repair guide if you can’t find it. This is not a time to pull out a mangled wire coat hanger. You don’t want to risk accidentally poking into any sort of gasket or conduit near the firewall. Instead, a spray gun is an ideal tool for the job.
4. What Causes the Sloshing Sound by Your Fuel Filler Cap?
Some cars have a drain near the gas cap/fuel filler flap, which can easily get clogged by rust and road grime. This drain tends to be pretty small, and you will show itself with rust spots right at the edge of the gas cap.
How to Fix
This drain is usually very long and typically comes out directly at the bottom of the car. So, it’s probably better to go with a siphon spray gun tool over a bent-up coat hanger.
If you can’t suck or blow the clog out and the water sloshing returns, your fallback option is to use sturdy stovepipe wire.
5. A Noise Of Gushing Fluid Coming From Overhead
If the sloshing sound is coming from overhead, and you have a sunroof, then chances are good there’s water in the drain channel or the roof drain. The even bigger worry here is that if you don’t fix this promptly, rust could develop, which could weaken the weather seal. Then you’ll be dealing with a leaky sunroof and a clogged roof drain that lets water pour in!
How to Fix
To find the drain, you’ll need to follow the natural contours of the sunroof and the roofline of the car. They’re meant to let gravity pull the water down, with the tiny drain being at the lowest point. The drain port is usually pretty small, which makes it easy for pine needles, bugs, and road gunk to clog them.
6. Water Sloshing Sound Coming from the Back of the Car
Sloshing sounds in the rear quarter panels often show up when you accelerate hard. You might even find water in the trunk without any obvious trunk lid leaks. This is one of the more common causes of the quarter panel and rear wheel well rust in a lot of older cars.
How to Fix
The drain ports on the rear quarter panels can vary from one automaker to the next. If you can’t find them in the lower portion of the wheel well, they might be integrated into the jack plate.
7. Water Sloshing Sound in the Footwell or Near the Firewall
If you’re hearing water sloshing sound from under the hood when you stop, and you’ve been running your air conditioner on a long drive, you might have a clogged evaporator drain. Normally, when you run your car’s AC, a small amount of moisture builds up along the evaporator.
The condensate drain underneath is designed to let that moisture drain away harmlessly. This is why you often see little wet spots under a parked car with the AC running.
If that drain is clogged by debris or mold/mildew buildup, the moisture has nowhere to go and will simply slosh around with the motion of the car. You’ll usually hear it more on the passenger side near the footwell. If the clog and sloshing sound have been going on for a while, you might notice moisture in the passenger side flooring and the telltale musty odors of mold buildup.
How to Fix
You’re going to have to crawl under the car a little bit to find the condensate drain hole. It’s usually on the passenger side near the firewall. Most have a relatively large port, which might be big enough for you to stick your pinky in.
Jabbing around with a coat hanger is a bad idea, as you risk accidentally puncturing sensitive air conditioning components.
8. A Water Sloshing Sound Coming from Inside the Glovebox
The sound of water sloshing inside the glove box or the passenger side dash could be a sign that there’s air in the heater core. It’s usually located deep inside the passenger side dash behind the glovebox, though most are so deep in that you can’t directly access them to check.
The worry here is that the sloshing sound is typically due to low coolant in the engine cooling system. So, you’ll likely notice the engine has been running hot and might even overheat. If you check the reservoir with the engine cooled down, the coolant line is probably under the LOW mark.
How to Fix
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Fixing air in the engine cooling system isn’t as easy as pouring more antifreeze and water into the radiator cap. You’ve got to purge or bleed the air completely out of the cooling system. This is something you might be able to do on your own if you’re a reasonably capable DIY mechanic.
If you aren’t comfortable doing this yourself, most mechanics will charge you around $125 to $175 for a complete radiator flush and fill.
Of course, the larger concern you have here is how did the coolant got so low in the first place? So, make sure to check for signs of coolant leaks inside the engine bay and the exhaust for any white smoke. If you do see white smoke, then it likely means you have a blown head gasket or cracked cylinder head, which is letting coolant escape via the combustion chamber.
Frequently Asked Questions
What Are Signs of a Mold or Mildew Problem in My Car?
Water trapped inside body panel drains, doors, or the car’s interior can quickly become a prime breeding ground for mold and mildew, especially in the summer or during warm weather.
The first sign of a mold problem is your car having a musty odor, even if it’s impeccably clean. It often builds up in the passenger footwell when the AC condensate drain port gets clogged. You might also notice a slimy spot or gray splotches on upholstered surfaces that are out of the sun.
In a scenario like this, you’ll need to clear the drain clog. Then you can try to kill the mold with a hydrogen peroxide-based cleaner. Bleach is a bad choice, as it can damage fabrics and is so volatile that it can’t kill the microscopic roots of the mold the way hydrogen peroxide can.
No More Sloshing Surprises
Most of the time, sloshing sounds are caused by a clogged drain in a door or body panel. The location of the sound will help clue you in on what’s clogged. Once you find the drain port, poke it open with a bent coat hanger, bamboo grilling skewer, paper clip, or a siphon spray gun tool.
After you’ve checked all the door and body panel drains, your attention needs to turn to the car’s AC drain port and/or the coolant system. If the drain port has road debris in it, the moisture condensation in the system simply can’t run out, and it pools up in the condensate pan, where it can easily cause mold and mildew problems.
If the sloshing sound is coming from inside the passenger side dash or behind the glove box, you might have air in your cooling system. You’ll need to purge the air and refill the coolant, then dive headfirst into figuring out why you had low coolant in the first place.
Written By
Jason Farrell
Jason Farrell is a certified master technician, the editor of Mechanic’s Diary in Pittsburgh, Pennsylvania. He is ASE (Automotive Service Excellence) certified and earned a Bachelor’s Degree in Automotive Technology from Pittsburg State University. With nearly 18 prior years of experience in the automotive field, he has extensive knowledge about Domestic, European, and other foreign makes and models of cars and light trucks. Jason’s experience working as a technician and service manager at dealerships, gave him the experience and know-how of most aspects of inspection, diagnosis, and repair from engine and drivability to electrical, HVAC, brakes, steering and suspension and everything in between.