Leaky Car Interior: Causes You May Not Know And Solutions

There’s nothing as frustrating as finding random mystery wet spots inside your car’s interior! But how did it get there? Finding where the water collects isn’t hard – Knowing well water obeys the law of gravity, it usually collects in the lowest spot, the foot wells! where the foot carpets are placed. But diagnosing where it came from is notoriously hard and must be dealt with promptly because of the many serious problems it can cause. If water sits for too long in a car’s carpet, mold can grow and cause bad smells. Other problems can include corrosion of pin connectors, computer failures, sensor failures, rust, and high humidity inside the car causing your windows to fog up.

Tracing The Leakage

A good way to know where the leakage is coming from is first to know WHEN it happens? Is it after a rain storm or car wash? Only when the car’s parked on a slope? Or maybe the AC? Identifying when can potentially narrow down where and why. Another strategy is to check for water marks, stains, or even signs of rust. Take a close look at connectors for corrosion and check brackets for rust spots; you will be amazed what you will find when you look for it. Water leaks are hard to pinpoint, but once you find exactly where the water is coming in, you can access the problem spot and repair it.

Potential Causes Of Leakage In Cars


If your car has a sunroof, this is likely the first place to check. One of the biggest causes of in-car leaks is the sunroof, even when factory installed, and aftermarket units are notorious! They are known to leak by design – the seal is not usually totally waterproof – but there will be a channel around the sunroof aperture which allows water to flow down drain tubes in the corners, which then run down the door pillars and down to the ground.

Often a leak that only occurs when the car is parked on a slope can be attributed to one or more of the sunroof drain tubes becoming blocked. To test – open the sunroof and poor a small amount of water into the drain tube.

Does it go down straight away, or does is drain very slowly or not at all? The water may even pool in the drain channel, run across the headlining and either drip out of the courtesy light, or even run down the A-pillars and into the carpets.

To fix it you need to find where the drain tube goes, (usually down the A pillar) and disconnect the end and blow through it with an air line – be aware that a surprising amount of filthy smelly water may come out! You may also have luck snaking the drain tube the same way you would the drain on your sink, only with a piece of ordinary wire instead of a pipe snake.

Windshield Rubber: 

This is applicable to both the front windshield and rear window – If the rubber surround dries out and cracks, or shrinks, or is fitted incorrectly, water will come into the car. If you’ve recently had glass replaced and that has coincided with a new leak this could well be the reason. Having the glass refitted with a new seal is the proper cure, but it is possible to warm up anti-rust coating until it is thin like water, pour it into the suspect area, and then clean up later with solvent.

Cabin Air Filter:

Some car’s cabin air filters are installed in the engine compartment, on the fire wall just in front of the windshield. This type can be prone to leaking on some models unless fitted correctly, and the lid secured. If there is any sign of damage to the seal you should replace it.

Air Conditioning:

Have you ever noticed a pool of water under your car on a hot day after the air conditioning has been on? This is perfectly normal. Sometimes, however, the drain tube can become clogged and cause the water to collect until it finds its way behind the dashboard and into the front carpets. Try not using the AC (or defroster as this sometimes triggers the AC system) and see if the problem persists.

Heater Core: 

If there is a leak, and the inside of the car smells like coolant (a sickeningly sweet smell) when it gets warm, the heater core may have sprung a leak. Check to see whether the liquid collecting in the car is antifreeze (Coolant) or water (Don’t taste it! Smell it!). Another good indication is if the liquid is only collecting on the passenger side, where most heater cores are located.

The heater core is like a little radiator which water passes through under the dashboard to heat the cabin. If the core corrodes, or one of the connections comes loose, it can leak into the car. Heater cores can be very difficult to access as they are generally buried away behind the dashboard, but if it’s leaking a replacement is often the only fix. In an emergency, the heater hoses can often be routed to bypass the core temporarily.

Window Seal:

There is also the rubber seal that rests against the side windows – the bit the glass rubs against when you wind them up/down. If this isn’t tight on the glass it can let too much water enter the door cavity (a little is to be expected). When that happens it can end up overcoming the membrane and soaking into the door panels to cause a leak. As with the door seals a visual inspection should be able to identify if this is a likely the cause.

Door Seal:

The rubber seal around the edge of the door can also sometimes be a cause of leaks. If the seal gets damaged, or dries out, water will track down the front of the door and into the car. A visual inspection is usually sufficient to diagnose whether this is the culprit. If the weatherstripping is not 100% replace it.

Door Membrane:

Behind the door panel there is a plastic or foam membrane, designed to keep moisture that makes its way into the door from getting into the interior. Water can enter the body of the door when it rains, and generally drains out of holes in the bottom. The door is sealed all the way around by weatherstripping, and holes are situated so any water drains to the exterior, on the other side of the seal..

If the membrane gets ruptured or torn, or the drain holes get plugged, water can run down the membrane and soak into the door panel. If you’re getting a pool of water in the foot well, check to see if the bottom of the door is damp or has evidence of water staining. If it does, whip the door panel off and check the condition of the membrane. Use waterproof tape to repair any tears, or replace the membrane entirely with plastic sheet.

This been said,  there’s not much point in drying out the car until you identify and stop or at least lessen the leak. Once you do though, you really need to dry out the inside of the car thoroughly because a damp car will go moldy very quickly. Even if it looks clean, there could be mold in the carpet or doors, and you could find yourself driving a car that smells like a compost manure.

We have experienced professionals that can trace any leakage in your car and stop it. Please follow this link Check My Car For Leakage Fill out the form and a professional will contact you within 24 hours.

About Nonso Okafor

I've worked as a technical support representative in major auto centers in Nigeria for more than twenty years. I have dealt with a variety of problems in my capacity as a customer service representative and auto diagnostics expert. I'm committed to assisting people in properly maintaining their automobiles and in appreciating this magnificent innovation known as an automobile.

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