Identifying And Repairing a Sloshing Sound In Your Car

By: Editorial Team

If you have experienced a sloshing sound in your car’s interior, you have likely wondered what caused the sound and how to stop it. The most common causes of this noise are:

  • A clogged evaporator condensate drain.
  • Low coolant.
  • Air in the coolant system.
  • A clogged door drain.
  • A leaking sunroof.

You should not ignore sloshing sounds within the vehicle’s cabin. If the noise is caused by water accumulation, it can lead to the growth of undesirable bacteria such as mold or mildew, which can cause a musty odor in your vehicle. Depending on where the sound is coming from, there may be several different causes and solutions.

1. Air In The System’s Coolant

Even if the coolant level in your vehicle is normal, a leak can still cause air pockets to form in the cooling system, which can cause a sloshing sound from the heater core behind the dashboard. You can occasionally remedy sloshing noises by refilling the coolant reservoir to a low level and properly filling it during an oil change. However, this is not sufficient to eliminate the noise in most instances. Here are steps for handling such a circumstance:

  • Start your car’s engine and allow it to idle for two minutes to get the oil and coolant moving. Then, listen to the sloshing sound.
  • Remove any overflow bottles from your vehicle and then turn off the engine. If your vehicle does not have an overflow bottle, you can skip this step.
  • Remove the coolant from your radiator and heater tubes using a shop vacuum.
  • After refilling the cooling system with coolant to its maximum level, allow the engine to idle for two minutes. If it becomes hot, turn off the engine and let it cool.

If you still hear water sloshing when you accelerate after attempting all of the above, it is likely that your air cooling system is no longer functioning properly and may need to be replaced.

2. Clogged Evaporator Drain

When you turn on your vehicle’s air conditioning system, moisture forms along with the evaporator coil and drips into a condensate drain pan then drips underneath the vehicle. If the drain is clogged or not draining properly, water will collect in the pan and make a sloshing sound as the vehicle moves. The stagnant water in the evaporator condensate pan provides ideal conditions for mold growth and can also cause water to leak onto the floorboard of your vehicle.

Symptoms of a clogged drain include water sloshing from behind the dashboard, which is audible during turns and braking. Another symptom is a damp floorboard; if too much water builds up in the pan, it can leak into the vehicle’s interior. These are the steps for How to Unclog a Drain:

  • Locate the evaporator drain tube beneath the vehicle and blow compressed air into the hole. When you blow compressed air into the drain tube, filthy, moldy water may gush out, so wear safety glasses and keep your face away from the drain tube.
  • You can attempt to unclog the drain without compressed air by inserting a flexible wire into the tube hole. Please give it a good jiggle to loosen any grime accumulated in the drain.

3. Low Coolant

A low coolant level can cause a sloshing sound from behind the dashboard when the engine is running. The sound is most noticeable immediately after starting the vehicle. Most vehicles’ heating systems utilize warm coolant/antifreeze from the engine block to heat the interior. When the coolant level is low, air bubbles may form in the system, causing the heater core to emit a sloshing sound. Solve this issue can by taking the following steps:

  • Check the level of coolant.
  • If the level is low, fill the reservoir with coolant until it reaches the recommended level.
  • If the coolant level drops after a few days or weeks of driving, there may be a leak in the cooling system.

4. Leaking Sunroof

Possible seal deterioration between the sunroof and the surrounding roof can occur. Water will enter your vehicle each time it rains, or you wash it if this occurs. As the water drains down to the drain holes, not all of it may be able to escape immediately, causing sloshing sounds while driving. Follow these steps to diagnose and unclog your sunroof’s drain holes if this occurs:

  • Open the sunroof and take note of the screws holding the headliner around the sunroof in place.
  • Open the plastic cover using a head screwdriver to expose the four corners of your car’s headliner.
  • Find a small drain hole beneath the headliner by removing it so you can see beneath it.
  • Use a towel to remove debris from the hole, a knife to remove excess debris, and a bucket to prevent your vehicle from becoming soiled.
  • Obtain a hose and use it to reach down into the hole and rinse until all debris has been removed.
  • After removing all debris, dry the vehicle’s interior with a towel and replace the clamshell plastic piece by snapping it back into place.
  • After applying glass cleaner, the sunroof should function again, and all dried-up water stains on the headliner should vanish immediately.
  • While you are up, replace the headliner cover; if necessary, remove any excess material from the sides of the window that has not been cut away.
  • Once everything appears in order around your car’s sunroof opening, reinsert the two screws you removed earlier to hold the headliner in place.
  • You are now finished, but if water continues to drip into your car, you must locate the source of the leak and repair it.

4. Clogged Door Drain

The car doors are not waterproof; water can enter through the window seals when it rains or when the vehicle is washed. The water then exits the vehicle through the drain holes located at the base of the doors. Dirt and debris can accumulate and clog drains over time. If you hear a sloshing sound while the vehicle is in motion, especially when braking or accelerating, the cause could be clogged door drains. You can remedy the situation by:

  • Park your vehicle in a quiet place.
  • Quickly open the doors and swing them back and forth. If you hear a sloshing sound, water has accumulated within the door due to a clogged drain.
  • Find the drain holes beneath the door and blow compressed air into each hole.
  • If you lack access to compressed air, you may insert a flexible wire into the holes and wiggle it vigorously. Keep your face away from the drains because filthy water will be gushing out of the holes.


1. Can A Cooling System With Insufficient Water Cause Water Sloshing?

When you accelerate or drive up a hill, an underfilled cooling system can cause water to slosh around your vehicle’s interior because there is not enough coolant to handle the engine’s heat and nothing left to prevent overheating. A common cause of this issue is that people neglect their radiators until too late. If this occurs several times over a long time, there may not be enough coolant left in the system to keep things running when you drive short distances or remain stationary.

2. Why is Water Sloshing Around In The Trunk?

A few things could cause water to slosh in your car’s trunk. First, leaves, dirt, or other debris could clog the drainage system, preventing proper drainage. If water accumulates in your car’s trunk, clean out the drainage system to prevent further damage. If you’re not comfortable getting under your car, take it to a mechanic. If water still sloshes after cleaning the drainage system, you may have a bigger problem and should have your car inspected by a professional.

3. Why Is The Splashing Sound So Loud In Some Cars?

The water sloshing sound is so loud in some cars due to the amount of noise-canceling material in the interior of the vehicle. Some vehicles have little or no noise cancellation, whereas others have substantial noise cancellation. If the interior noise-canceling material is ineffective, you will be more likely to hear a sloshing sound when accelerating or climbing hills. It is especially true if the coolant levels are low and the engine has previously overheated.

4. Can a Faulty Air Conditioning Compressor Cause Water Sloshing Noises?

A faulty car AC compressor can cause water sloshing sounds within the vehicle, but this would be due to the component’s inability to withstand the heat. In most instances, engine overheating is the cause of the water noise, not the AC compressor.

If you hear water sloshing inside your vehicle, you should have a diagnostic performed to determine the source of the problem. You may have multiple problems with your car simultaneously, or you may not know the cause of all of these symptoms. In either case, you should consult a professional.

5. What Can Cause Water Leaks in Your Car’s Cabin?

There are numerous potential causes for interior water leaks in a vehicle, but the following are among the most common:

  • A malfunctioning windshield wiper motor
  •  A damaged window or door frame seals
  • Cracked or shattered windshields