water sloshing sound in car

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.

  • Paper Clip – When bent out and straightened, it can help clear tiny drain ports like you often find in rocker panels and rail drains.
  • Metal Coat Hanger – When bent straight, it provides a fair amount of ramming force, which might help clear rust jams out of door drains and quarter panels. Just be careful not to do it in more sensitive areas, over as it can damage rubber gaskets and scrap metal finishes.
  • Stove Pipe Wire – A middle-ground tool that isn’t quite as robust as a coat hanger but still has enough strength to help you ram out small clogs. You can also bend it into unique shapes for hard-to-reach drain ports.
  • Bamboo Grilling Skewer – It has a sharp tip and a fair amount of ramming force potential. Yet it’s made of wood and less likely to scuff and scrape sensitive metal components.
  • A Blow Gun Tool – This somewhat uncommon tool connects to an air compressor line with a flexible plastic siphon tube attached to the end. You can get it into all kinds of hard-to-reach places, and the jet of air can help blast a clog away without any risk of scraping or scratching sensitive components. It also tends to make a different noise when the jet of air finally clears the end of the drain to let you know that you truly did get it all.

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 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

How to Get Water out of Vehicle Door!

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.

  • Step One: Find the drain itself, which usually looks like a little rubber bung in the lower portion of the door. Some automakers put them right in the corner.
  • Step Two: Use a wire coat hanger or a wooden bamboo skewer to clear the blockage in the door drain. In a perfect world, the water would drain out on its own, but you might need to park the car on an incline to let gravity fully drain every drop out of the interior of the door.
  • Step Three: Test the door again by moving it back and forth, going for a short drive, and braking hard. If you still hear sloshing water sounds, the door drain might need to be cleared, or you have additional clogs in other body panels.

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

Water in Miata rocker panels.

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.

  • Step One: Locate the drain; it probably doesn’t have a rubber gasket port and is just one or two small openings in the door sills.
  • Step Two: Use sturdy stove pipe wire or a robust paper clip to ram through the port. There’s usually a fair amount of rust and/or road grime blocking them.
  • Step Three: Once you finally get the water draining out, be prepared to wait a while for the tiny ports to let it all drain away.

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

Water Sloshing Sound Coming from the 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

Windshield Runoff Drains

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.

  • Step One: Locate the front drain. There might be two of them.
  • Step Two: Insert the air spray gun and give it a few blasts of air to confirm that you’re in the drain. You might hear more water sloshing.
  • Step Three: Fish around by feeling until you make contact with the lower portion of the drain.
  • Step Four: Give it several solid blasts of air. When the drain first clears, you might notice a change in the air’s sound at the end of the spray gun.

4. What Causes the Sloshing Sound by Your Fuel Filler Cap?

A Sloshing Sound By the 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

Clearing fuel filler drain holes.

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.

  • Step One: Insert the spray gun into the top part of the drain.
  • Step Two: Give it one or two short blasts of air. If the port is indeed clogged, you’ll hear a water sloshing or bubbling sound.
  • Step Three: Keep working the tip of the tubing down with one to two-second blasts of air. You’ll probably notice a change in the sound once the blast of compressed air blows the clog out of the bottom of the car.

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

A Sloshing Sound 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

How to unclog a sunroof drain

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.

  • Step One: Locate the drain. It’s usually in the back corner of the sunroof frame. There might be one on each side. Though you might need to remove the weather stripping, an air dam bar, or other hardware components to get clear access to the rooftop drain port.
  • Step Two: Use a shop vac hose to suck out any loose debris, dust, and grime. Otherwise, it’s just going to find its way into the roof drain in a few weeks, and you’ll be back to square one.
  • Step Three: Insert sturdy stovepipe wire or the tip of the spray gun tool and push it in until you feel something blocking the end.
  • Step Four: Give it several blasts of air or ram the wire into the blockage until it comes loose. You’ll likely notice water draining out under the car or the quarter panel.

6. Water Sloshing Sound Coming from the Back of the Car

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

Water sloshing quarter panel drain hole 2013 Mustang GT

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.

  • Step One: Locate the quarter panel drain port.
  • Step Two: Use a coat hanger or a sturdy paper clip to poke out the clog.
  • Step Three: If the water stops flowing out, give it a few more rams, as it’s likely bits of rust are being drawn to the port by outflowing water. Essentially re-clogging the drain.
  • Step Four: Remove any rust from around the port to help it stay clear in the future.

7. Water Sloshing Sound in the Footwell or Near the Firewall

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

How to unclog your car AC drain line

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.

  • Step One: Locate the condensate drain.
  • Step Two: Use a needle nose pliers to pull out any obvious organic debris and see if the water starts flowing again.
  • Step Three: Use the spray gun tool to clear any deeper clogs that might not be visible from the drain port.

Jabbing around with a coat hanger is a bad idea, as you risk accidentally puncturing sensitive air conditioning components.

  • Step Four: Start the car and run the AC for 10 minutes, then look under the car to confirm that water is dripping from the condensate drain once again.

8. A Water Sloshing Sound Coming from Inside the Glovebox

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

How To Purge Air Out of a Cooling System! [FREE and DIY Method]

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.

Jason Farrell

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.

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