How to Fix the Sloshing Sound in Your Car

Water sloshing in your car can be due to several reasons, including spilled drinks, moisture from the A/C system, or rainwater entering the cabin through a leak. But in truth, there is more to that audible sloshing you hear whenever you speed up, make turns, or come to a stop. This guide will highlight the components responsible for producing the bothersome sound and discuss how to fix the sloshing sound in your car.

Fixing the sloshing sound in a car entails reinforcing rubber plugs and seals, replacing worn parts and weatherstripping, unclogging drain holes, burping the radiator, and veering away from debris-prone parking areas.

Despite how straightforward it is, water sloshing is not exactly something you can delay resolving. While the sound itself may not cause any imminent danger, it could indicate a more serious predicament.

Prolonged water accumulation in a vehicle creates an unpleasant driving experience due to mold growth. When left unattended, it leads to corrosion, damage to electronics, and other internal system malfunctions.

Causes and Problem Areas

1. Drain Holes

Plugged drainage holes are arguably the most common cause of vehicle water sloshing (most noticeable when the car is parked). Functionally, they allow water to drain away from a vehicle. They may also cause a four-wheeler to develop water buildup in areas like the car door, wheel wells, or around the sunroof (if a vehicle has this feature).

Note that not all drain holes belong to one vehicle system — meaning that you may need to look into the fuel tank, HVAC system, and even the battery compartment if no water buildup is found in more prominent areas.

It would also be best to inspect the drain hole itself and see if its size is up to spec, as some drain holes clog more easily than others due to having a smaller-than-normal hole diameter.

2. HVAC System

As mentioned, faulty drain holes and A/C components can cause water sloshing noise. Specifically, you may hear the sound coming from the dashboard. What is certain in this scenario is that water has found its way into the drains and A/C ducts. But as to how, it could be due to a leak, a defective heater core, or another related issue.

The HVAC system has an evaporator drain that removes condensation from the evaporator and away from the entire system. But if this drain is blocked or damaged, condensation cannot escape, resulting in water accumulation in the A/C ducts.

When this happens, you may get a whiff of an unpleasant musty odor, accompanied by dampness on the carpeting in front of the A/C outlet (below the passenger seat). Apart from this unwelcome stench, water sloshing in the car is often characterized by its occurrence, specifically while taking sharp turns or braking.

3. Windows and Weatherstripping

Car windows per se are not enough to cause the water sloshing sound in your car. But when they are left open when parked outside, during heavy rains, or when they have deteriorated weatherstripping, they become an easy access point for water to seep through areas inside the vehicle where buildup can occur.

Depending on how much water has accumulated in a given area, water sloshing may or may not be noticeable when turning or accelerating.

4. Seals

Since seals prevent the entry of water and other elements into the vehicle interior, it is crucial to keep them from deteriorating to avoid that water-sloshing sound in your car. When faulty, seals allow water to seep through a car’s bodywork. As such, normal wear and tear or accidental damage are not always to blame for seals going bad.

Seals are almost everywhere on a vehicle, including car doors, window sills, transmissions, differential, wheel bearings, axle shafts, and the engine. Hence, it only makes sense to check all these areas if the sunroof, trunk, or windshield checks out for water accumulation.

Slightly deviating from the topic, rubber plugs under the sill can also fill with water. Plugs are not necessarily in the same category as seals but function similarly.

Perhaps, a significant difference between these two is that rubber plugs do not provide a watertight seal like actual seals do. Nonetheless, they still help reduce water infiltration and should be kept in as good a condition as the seals protecting the different areas of a vehicle.

5. Extreme Water Fording and Flood Damage

For off-roading enthusiasts, crossing shallow streams and traversing flooded areas are part and parcel of the “great outdoor experience.” And while these are fun activities, they are also some of the most damaging undertakings a vehicle will have to go through — simply because of the probable damage to that car’s electrical and mechanical components, on top of corrosion and water sloshing.

Components most likely to collect water as a result of these activities include the trunk, undercarriage, and engine bay:

• Trunk: High water levels can seep through damaged or clogged drain holes and the seams of the trunk lid.
• Undercarriage: Water can enter through the wheel wells and door sills if a vehicle’s undercarriage is submerged. Suppose the water level is higher than the height of the undercarriage. In that case, it can permeate the cavities and pockets within the rocker panels up to the passenger compartment — leading to damp carpets or floorboards (view on Amazon).
• Engine bay: Water enters the engine compartment through the intake system and relevant openings, which is the most likely in the lot to cause electrical or mechanical damage to certain components.

6. Vapor Barriers

Vapor barriers in car doors that were either damaged or not reinstalled after a DIY mod can lead to water stagnating inside the doors, creating a sloshing sound.

This can be problematic, as water can damage computer modules and speakers installed inside the doors. The stagnant water can also strip the paint from the metal, causing rust. Moving components inside the doors, like the window motors, can get water damaged and would likely warrant replacement.

7. Suspension Mods

It is common practice for off-roaders to perform suspension mods on their rigs to raise the stance of their vehicles. But some folks do the opposite — that is, to alter the geometry of their vehicle’s suspension system by lowering it down. When a four-wheeler undergoes this modification, it increases its susceptibility to water infiltration (which leads to water sloshing).

An incorrectly set up suspension system is usually to blame in this scenario. But even if it were done properly, suspension mods can still cause water to accumulate in certain areas of the vehicle, like the wheel wells and undercarriage.

In like manner, installing stiffer suspension components can cause water to be displaced more forcefully, leading to increased sloshing sounds.

8. Radiator and Head Gasket

If the sloshing sound in your car is gurgly and seems to emanate from somewhere deeper in the front section, the source could be traced to your radiator. This is because the sloshing sound is produced when air gets in the radiator through leaky lines. This resonance is typically heard when starting a vehicle, as the process activates the radiator to regulate temperature or during deceleration.

A blown gasket is another reason to hear sloshing from your car’s front end. It may not necessarily sound gurgly like the sound from the radiator, but it shares the same trigger — air has gotten into the component and disrupted its normal function.

It is particularly a little more serious than other flawed components — not to mention that a malfunctioning gasket causes a radiator (view on Amazon) to go awry since it keeps the engine and cooling system components from overheating and developing air leaks.

9. Design Flaws in Vehicle

Certain makes, such as some Volvo cars, have sunroof designs that allow water to permeate the cabin when it rains. A shallow reservoir around the sunroof’s perimeter that collects water and routes it to runoff points through the A-pillars has been offered by the OEM as a quick fix. However, no design alteration has permanently (and more sensibly) resolved the problem — resulting in unknowing buyers bearing the aftermath of owning a car prone to sloshing and water infiltration.

Other design flaws leading to water sloshing are as follows:

• Poorly designed air intake
• Ill-conceived windshield wipers
• Inadequate drainage in the car’s undercarriage
• Aftermarket side steps for trucks, SUVs, and other 4×4 vehicles

10. Humidity and Ambient Temperature

In case you are wondering, humidity (the amount of moisture in the air) and outdoor temperature (the temperature of the surrounding air) are two facets that indirectly contribute to the water sloshing sound in your car.

All sorts of adhesives in your cabin soften when humidity is high or outdoor temperature reaches over 40° (which can translate into deteriorated weatherstripping, seals, and gaskets). More importantly, high humidity levels increase the amount of moisture present, which has the same effect on condensation inside a vehicle.

A higher propensity for water accumulation should not automatically be a problem for car owners, provided the collected water is properly drained or evaporated. However, it especially becomes a concern if a vehicle is already compromised in one of the above areas.

How to Fix that Car Sloshing Sound

1. Check the weatherstripping

First, inspect if the sloshing sound is coming from your vehicle’s interior. Check if the weatherstripping around all doors and windows is worn or damaged (as it can easily let water enter your cabin if compromised) and replace them as needed.

Depending on how long this issue has been left unnoticed, you may feel dampness on the side of the car door where the water leak is. Or worse, a water puddle may already be forming on the carpeting or floorboards.

2. Locate the source

Next, locate the source of the sloshing sound if coming from the fuel tank, the cooling system, or a clogged drain under the windshield cowling.

• If the water sloshing sound in your car emanates from the fuel tank, see if there is an issue with the fuel system. Verify that the fuel level is up to spec and not sparse or overfilled. Otherwise, drain the excess or top it off until the fuel is at the appropriate level.
• If sloshing is coming from the cooling system, inspect the coolant level and make sure it is sufficient. If low, add more coolant to the reservoir. After which, confirm whether or not there are air pockets in the system. You may need to bleed the cooling system to remove any identified or suspected air pockets. Determine if other HVAC components are also at fault (for instance, the heater core).
• If the drain under the windshield cowling is suspected, verify that it is not clogged. Use a small wire or a coat hanger to ensure this.

4. Check the passenger side floorboard

If the first three areas check out, see if water is accumulating on the passenger side of the floorboard. To confirm, open a plug at the bottom of your car or remove the carpeted flooring where the passenger puts their feet.

You may require the removal of some plastic parts and unscrewing some nuts under the seat to access this section, but nothing more. Prepare for a mess when doing this step, as most vehicle models have carpeting glued to about 12 inches of foam that gets especially bulky when soaked in water. 

5. Remove the water

Once you have removed the carpeting, you may do the same with the foam (or only a section). In whichever case, you will access the exposed painted metal bottom of your vehicle, presumably with several inches of water in it. Suck out the collected water with a pump or siphon until you have gotten most of the wetness out.

6. Continue to remove any new water pools

After getting the initial water buildup out, leave your vehicle for a few days to let the water in the foam come out. Then, suck out any new water pools that have formed. You have to repeat these two steps several times. After which, leave the foam and the vehicle for a bit more to let them dry.

7. Remove the debris from drains

For clogged drains, determine which specific drain is impacted:

• Sunroof drains
• Convertible top drains
• Door drains
• Trunk drains
• Body panels and rocker arms
• Battery tray

Once you have identified the problem area, use a flexible snake wire to remove debris. You may also use compressed air or a soft brush to push out obstructions in the drain hole. For any of these drains, be careful not to use excessive force when cleaning the holes, lest you damage the drain tubes.

For impacted car doors, feel along the rubber gasket on the bottom of the door, open it using your fingers, and see if water droplets start pouring out. If yes, keep the gasket open and let the water drain out.

Pull out debris and other obstacles in the drain hole using the abovementioned method. But if there is too much debris, removing the door card and cleaning it out from the inside cavity is the best way to ensure it does not accumulate water afterward.

The battery tray and rocker arm drains are more difficult to clear than the other orifices. Hence, outsourcing the cleaning task to a professional may be best if you are not that familiar or comfortable with these components.

8. Inspect the radiator or head gasket

Sometimes, the culprit could be your radiator or head gasket — so inspect them too. However, if your gasket is intact but the air still needs to get out of the system, you might consider “burping” your radiator. Do this by tipping your car on an incline to raise the front end. Then, remove the radiator cap and turn your vehicle on. 

Once the car is on and the radiator starts functioning, the incline will assist airflow to the radiator cap. The coolant will start moving through the system whenever the engine reaches the regulation temperature. When this occurs, squeeze the hose connecting the radiator cap to the coolant reservoir, manually assisting the air out.

Typically, performing these fixes is enough to resolve the issue and get rid of water sloshing. But if the sloshing sound persists, you may have a leak still waiting to be addressed.

Check for leaks and remedy them as you go through the above steps. That way, you need not redo the process of cleaning your drain holes and eliminating the water sloshing sound in your car more than once.

Conclusion — How to Fix the Sloshing Sound in Your Car

Given the critical role of the HVAC system, seals, and even your radiator in keeping your vehicle waterproof, the health and integrity of these components are not something you would want to ignore or leave unchecked for a long time.

With cars constantly subjected to varying ambient temperatures and the elements, any water accumulation will inevitably lead to serious malfunction and eventual damage to the affected parts and surrounding components.

The remedial steps outlined in this guide may be non-exhaustive, but they address the most common culprits behind your car’s gurgling, swishing, or water-sloshing sound.

Performing them to the T is critical to addressing the issue. However, precautionary measures like closing all doors and windows when parking outside or in flood-prone areas and performing regular vehicle inspection and upkeep work better in keeping that water sloshing sound at bay.