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How to find and repair a leak inside your car – Identifying wet floorboards or trunk well

The other day I was searching for my jumper cables in the trunk well in my car. Lo and behold I had a swimming pool where my spare tire sat. Luckily, I caught this before it caused any rust or odor.

Others are not as fortunate. Throughout the years, I have seen several cars with damp floorboards or a pool of water in the trunk. This problem is often ignored by most but can be an annoyance for others.

Have you ever got into someones car and took a deep breath of the wet towel funk? If you have smelled this before then you know what I am talking about. A musty, moldy, stale smell usually means one thing and one thing only – you have a water problem. Perhaps the car that you are thinking about is yours. There are a few tell-tale signs that you have a water problem:

  • Your car smells of wet dirty socks
  • Mold spores tend to form, causing allergic reaction for some
  • After a heavy rain your window are soaked on the inside with condensation
  • Interior of vehicle is damp
  • Metal components inside your car begin to rust

Dealing with a water issue is not as difficult as you may think. The source of water is usually easy to identify and correct. In fact, the majority of times it is simply a worn weather stripping or deteriorated caulking. Fixing this issue begins by first identifying the underlying cause.

Identifying the source of water coming inside car

Wet trunk spare tire wellFinding the water source is usually pretty easy but can sometimes be difficult. This is especially true if the source is coming from the firewall area high above the dash board. In most cases you can identify the source of water by using the following steps:

Remove paneling or carpet and dry out

The best way to start is to remove moisture all around the area. Snap off all plastic panels and pull back the carpet around the wet areas. This usually takes a phillips screwdriver and or some type of prying device. If you know where the fasteners are at, you can sometimes pull panels off with your bare hands.

In most trunk compartments and some floorboards a rubber plug can be pulled out or pushed through to release any pooling water. I find it easier to push them through and then retrieve from underneath the car.

remove tire well drain plugUse a towel or paper towels to dry up the area. This should be done on a sunny day with the windows down or doors open. You can also use a water extractor/ carpet shampooer. Running the heat on the floorboards with the windows down is also a good idea if you are working in the floor board. While cleaning up, take note of the color of the water. This is especially important if you are working on the floorboard of the car. If the liquid that is being extracted is green, there is a good chance that it is antifreeze and a component such as your heater core is leaking.

Powder the area with baby powder

Powder used for water detectionPowdered trunkOnce everything is good and dry, grab some baby powder, line chalk, foot powder, whatever you have around the house will work. If possible, chose a color that contrast the color of your car. Just a light layer will help to identify the trail that the water makes when entering your car. As a bonus, if the powder is scented it will make your car smell better. Well, better than mildew. Choose your weapon carefully as some products such as powdered sugar or flour may not be the best option.

Simulate rain conditions with a water hose

rain simulationClose all doors, windows and the trunk lid. Simulate a rainfall with your garden hose. It is perhaps better to use a shower nozzle for this. Spray around all channels and even places that you would never suspect water to get in. It is surprising the places that water finds its way in. When creating rainfall, remember that rain falls straight down and sometimes a little sideways. A 45 degree angle around each body panel should be more than enough. A car is not water proof, only water resistant so you do not want to force water into areas where rainfall would not naturally reach.

Allow the vehicle to dry off

Allowing your car to properly dry is good for two reasons. First, immediately opening the trunk or doors may introduce water into the car that can be mistaken for a leak. The second reason is that it gives time for even the smallest leak to find its way into the car. Give it a good 30 minutes or so depending on weather conditions.

Slowly open panels and look for leaks

Water intrusionWater entering cabinIn most cases, the issue will clearly present itself whenever you open the windows or doors. Slowly open each and closely inspect the area for water trails. The first place to start is usually the rubberized weather stripping around the edge. This is typically the first thing to get torn or dry rot. The water trail will usually point directly to the source. Having a flashlight handy is a good idea.

After identifying the source, determine the proper corrective action. Do you need to replace torn or rotted weather stripping, Does your rain catch sill need to be caulked? Are your drain channels clogged, causing a backup in your car? There are a number of reasons why water can enter your car.

Fix your leak

Rain water puddling in trunkOnce you have determined the source of the leak, fixing it is the most obvious step to take next. Fixing the problem is best accomplished using a common sense approach. If its cracked, chipped or broken replace or repair it. I have used 100% silicone to repair a tare in weather stripping before but this usually only works for a short period of time.

In the case of my vehicle, the culprit was unexpected. You may have read my recent post about replacing the lift arms on a hatchback lift gate. Although the replacement shocks work well, they may be a hair too long, preventing the trunk lid from closing all the way. After removing the lift supports and testing the theory, most of the water stayed out.

There was one spot where water was barely getting by. This is probably not enough to amount to much of anything but I will soon replace the entire weather stripping in order to achieve a tight seal.

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