Why Do I Hear Water Sloshing Around In My Car?

Turns out that “water sloshing” sound you might’ve heard in your car recently is actually normal, and there are a few easy explanations. Though often described as a sloshing noise, these answers still apply if you’ve heard water gurgling, swishing, and even trickling inside your car.

Any unfamiliar noise coming from your car can be cause for alarm, and, in most cases, it ends in a trip to the mechanic. But hopefully what will help you go from swishing, trickling, and sloshing to the peaceful hum of your engine or the luxurious absolute silence you miss is getting a better sense of the problem you’re trying to solve in the first place.

Exterior

Trickling Along the Line

Starting from the outside, if you hear water sloshing in your doors and/or above your head, it’s most likely coming from your exterior drain lines. These are the runoff points built into your sunroof (if you’re hearing this trickling over your head) and doors.

What your sunroof and doors have in common is that they’re openings to your car, which means they’re built with the extra care of making sure water doesn’t leak through to your interior.

Think about this like your car having gutters. The gutters on your house catch rainwater and guide it to the ground, and the drainage for your doors and windows do the same.

Sometimes, if you’re driving for the first time after rainfall, that water won’t empty all the way and will sit in your drain lines. The key here is that the sloshing sound should disappear once the vehicle’s motion helps any remaining water drain.

There’s also another drain line to consider! Let’s say you hear the sloshing noise coming from the passenger side of your car only. This could mean you have fluid in your air conditioner drain line. This line drains condensation away from the AC unit in your car and wraps around to the passenger side.

Just like above, if you take off and the resting water drains, leaving you to a quiet ride, then you’re home free. However, if the sloshing persists that’s a sign that you need to investigate.

Going back to our gutter metaphor, sometimes your gutters get clogged with debris. They won’t drain and you’ll have build-up and overflow. The same thing can happen to the drain lines in your car.

They can get stopped up with dirt, pine needles, leaves, and even bugs! So, your lines hold water indefinitely that’ll slosh around as your car moves (specifically when you accelerate, decelerate, and turn).

What to Do?

Thankfully, clogged drains can be an easy fix. Some of the top recommendations are using a wire to snake debris out, or you can use compressed air to push it out.

If you’re not sure where to start, some light research on the specific make and model of your car can help identify where the outlets should be. You might also be able to find videos or forums of people with your car who had the same problem and see how they resolved it.

But Wait, One More Thing…

There’s actually one more, less commonly known reason you might hear the water sloshing sound around you, and it’s still coming from your exterior…just not from your drain lines.

If you drive a truck, SUV, or off-roading vehicle that has side steps, it turns out those steps can hold water too! One of the reasons this isn’t commonly talked about is because rainwater doesn’t usually get stuck in there. But when you’re off-roading and cutting through water crossings, sometimes those steps will hold water.

If that happens, you’ll want to pay attention. Wait to see if the water drains and the sound goes away. If it doesn’t, you can usually detach the steps and drain them manually.

Then, make sure to check for any holes in the step so that you can seal them and prevent water from leaking in again.

Interior Sloshing

Water held in your exterior – whether it be drain lines or steps – usually makes noise when the car is in motion.

But, what about the sloshing sound you hear when your car is sitting still? Chances are this sound can be localized around your dash, behind your air conditioning and heating vents.

Remember how your AC has its own drain line, and how that can get clogged with debris just like the “car gutters”? Well, sometimes that drain line backs up into the evaporator compartment. If enough condensation builds there, you’ll be able to hear the water sloshing around like it’s right under the surface of your dash.

But, what if your sloshing is a little more gur-gly and it’s coming from somewhere deeper in the front end? This gurgling sound is probably traceable to your radiator. You’ll hear it when you start the car and the engine turns on, activating the radiator to regulate temperature.

On a basic level, the reason you’re hearing the sloshing sound from your radiator is that air somehow got in. Sometimes air comes in through leaky lines, replacing the coolant fluid that drips out.

A more common cause, that’s actually the source of a well-known phrase, is a blown gasket. Well, a blown head gasket to be more accurate. What this means is that you’ve broken the seal between the cylinder head and the engine block, creating space for air to get in.

This is a little more serious than backed-up car gutters because your radiator regulates your engine temperature, working to keep it from overheating. With the seal broken, pressure released, and air entering the reservoir, you end up without a properly functioning radiator.

What to Do?

Unfortunately, the solution here isn’t as simple as snaking your drain lines. If you’re confident in your car knowledge, or your knowledge of looking up helpful YouTube videos, there are some DIY options to consider.

Again, keep in mind the make and model of your car as it compares to whatever material you draw from for advice.

From a quick search, I’ve found three common DIY fixes that people have used with confirmed success.

  1. Fill her up! Essentially, a number of drivers were able to get rid of the sloshing noise by filling their reservoir with more coolant. The low level left the remaining supply to literally slosh around in there. By leveling it off, the radiator returned to normal function.
  2. If you have a blown head gasket, depending on the size of the leak you might be able to repair it yourself by sealing the break.
  3. If your gasket is intact but you still need to get air out of the system, you might consider “burping” your radiator. They key is to tip your car on an incline so that the front end is raised. Once you turn the car on and the radiator starts functioning, the incline will assist air flow to the radiator cap (which you will have removed so that the air can escape). The coolant will start moving through your system whenever your engine reaches the temperature at which regulation begins. When this happens, you can squeeze the hose that connects your radiator cap to the coolant reservoir, manually assisting the air out.

With that being said, popping the hood or shoving wires and air into the intricacies of your car can be intimidating, and there’s the possibility that trying to fix it yourself is only going to make the problem worse.

So, what then?

The Professional Fix

You could always…go to a mechanic! Understandably, this isn’t always the ideal solution because DIY fixes are typically cheaper than paying for professional labor. But, what’s even more expensive is making things worse by trying to make them better on your own.

So, if you aren’t sure or aren’t comfortable doing these repairs yourself, maybe start by asking a friend or family member who’s more familiar with cars if they can help. If not, you can start by having a mechanic assess the problem and they’ll give you an estimate before work would actually begin.

On the Other Hand…

Now that you know possible explanations for that water sloshing sound in your car, maybe you don’t necessarily care. Maybe, you’re not in any rush to run out and fix anything, or you might not have the cash or time to get these issues resolved right away. So, what happens if you wait?

Drain Lines

A little water sloshing around in your drain lines isn’t going to affect how your car runs or regulates itself. However, if you don’t unclog the lines water will continue to build up.

Eventually, the lines will be full and without anywhere else to go you run the risk of water leaking in through the access points to your interior. The same goes for a clogged AC drain line. The condensation will build up and might start leaking into your passenger side footwell.

Radiator

Considering the critical role your radiator and coolant play in regulating your engine temperature, this issue isn’t something you’ll want to let go of for too long. With your engine overheating, it’ll start to warp and melt some of the surrounding parts.

Similar to how a tiny break in the gasket can disrupt the pressure system and function of the radiator, misaligned, damaged, and warped parts throughout your car can have further damaging effects.

Now that you know why, when, and where the sloshing sound comes from, you can decide for yourself how to restore your car to that blissful hum or quiet.

Liam

Hi, I'm the initiator and writer of this blog. Cars were and will be my first love, and my favorite hobby, that's why I decided to start this blog and write about my discoveries and techniques to improve my cars or repair them.