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How is water leaking into my car?

Spraying a hose on a car to trace a leak

Wet carpet in your car's footwells? Find out what could have caused it and how to stop more rainwater from getting into your car.

How to find a water leak in a car

Finding water in your car isn't hard – the first sign will probably be steamed-up windows but It usually collects in the footwells - soaking into the carpet or actually forming puddles. But diagnosing precisely where it's getting in can be very difficult.

Water will always pool in the lowest area – but it can run along wires, travel up material/fabric surfaces and generally do its best to disguise where it came from in the first place.

The first thing you need to identify is when it happens. Is it after rain, when the car's parked on a slope? Identifying when can potentially narrow down the cause. If it leaks even when rain hasn't fallen, it's coming from somewhere within the car itself. If it only happens when the cars on a slope, it's probably a seal, or blocked drain tube...

What causes a water leak in a car?

1 Split door membrane

Usually only an issue on older cars, where the plastic film has perished, or on newer cars where the door cards have had to be removed to repair an electric window, for example.

Water can enter the body of the door when it rains, and generally drains out of holes in the bottom of the door. But if the membrane gets ruptured or torn, water can run down the membrane and soak into the door card.

If you're getting a pool of water in the footwell, check to see if the bottom of the door is either damp or has evidence of water staining. If it does, whip the door card off and check the condition of the membrane. The door cars (or inner trim panels) are secured by clips and screws. Use waterproof tape to repair any tears.

Door membrane

2) Door seal water leaks

Is the door seal in contact with the car when it's closed? One way to check is to sprinkle talc over the entire length of the seal before closing the door. Open the door and look for any parts of the car body where the talc hasn't been transferred. Also check the seals around the windows (front and rear) while you're at it.

Sometimes if the seal has become hardened, it can be rejuvenated with silicone spray or rubber restorer. If the seal is damaged, replace it.

Car door seal

3) Pollen filter leaks

Pollen filters can cause leaks if they haven't been fitted properly or haven't been changed in years.

Some filters are fitted in the engine compartment just in front of the windscreen – these are prone to leaking on some models unless fitted correctly, and the lid secured properly. If there is any sign of damage to the seal, replace it.

Car pollen filter

4) Heater matrix leaks

Water leaking into a car isn't always caused by rain. If the water smells like coolant, check to see whether the liquid collecting in the car is antifreeze. If it is, it could well be the heater matrix.

This is like a little radiator that coolant passes through to help heat the cabin. If the matrix corrodes, or one of the connections comes loose then it can leak into the car.

A heater matrix is tricky to get at because it usually needs the dashboard to be removed to access. Your Haynes Manual will show you how to do this.

Heater matrix leak

5) Leak from the rear screen wash

The rear screen's washer jet is usually fed from the bottle under the bonnet via rubber tubing. Sometimes the tube will split or becomes detached, and because it runs along the inside of the headlining, you'll be able to see and feel damp spots on the ceiling. The headlining will usually need to be removed to access the pipe.

6) Sunroof leaks

Sunroofs are by design intended to leak – 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 either mounted in some, or all of the corners.

Often a leak that only occurs when the car is parked on a slope can be attributed to the sunroof drain tubes becoming blocked. To test, open the sunroof and pour a small amount of water into the drain tube. Does it go down straight away, or does it 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 airline – be aware that a surprising amount of filthy, smelly water may come out!

Car sunroof

7) Windscreen rubber

This applies to the front and rear screens. If the rubber surround becomes perished, or is fitted incorrectly, water will come into the car. Have you recently had new glass fitted?

Having the screen refitted with a new seal should cure it.

Windscreen rubber

What to do once you’ve found a water leak in your car?

There's not a huge amount of point in drying out the car until you identify the leak, although a damp car will go mouldy very quickly, and you could find yourself driving about in a car that smells like a compost bin.

So once you've found and fixed the leak, remove as much of the affected trim as you can and mop up the water with a microfibre cloth, or kitchen roll. When you've got it as dry as you can either use a plug-in dehumidifier or one of the standalone units intended to prevent damp.

Some people swear by leaving a tray of cat litter in the car. It may take time to dry the car completely, though, so whenever you drive the car have the air-con on (with the heat turned up) to help, because that will also remove moisture from the air.

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