When water leaks into our vehicle, we need to find the source and stop it. Knowing where to look is helpful and this article provides several clues.

The difference in HVAC and environmental leaks

In our last Detailed Topic we discuss water leaking into the interior from the heating and air-conditioning systems. Water may also come from outside environmental sources, such as rain. Wet carpeting is the most common symptom people notice. With environmental leaks, this only happens after rain or washing the vehicle.

With water leaks originating in the HVAC system, a wet right front floor is the most common symptom. This may also occur with exterior leaks.  With the HVAC system, the problem often shows up every time we drive the car and not only after a rain. Heater and air conditioner leaks do not depend on rain or washing the vehicle to produce the symptom.

Seals on doors and the trunk

We may also find water in other parts of our vehicle. Water most often shows up in the trunk or on the front or rear floors on either side. When we notice a leak, the large body openings, such as the doors and the trunk are most often suspected. In fact, these areas are less prone to leakage than most people think. Door and trunk seals rarely cause leaks unless the vehicle has been in a poorly repaired collision. Often people replace these expensive seals only to find the leak persists.

How to find a leaking door or trunk seal

We can do a quick, initial check for leakage around these areas by slightly pressurizing the interior of the vehicle. Setting the air conditioning to fresh-air and turning the blower on high will accomplish this. This draws air into the vehicle and causes a positive pressure.

With positive pressure in the interior air will leak out of the same places the water comes in. By slowly passing our hand around the area where the doors and trunk seal, we feel air escaping at the leak points. Moistening our hand with water makes it more sensitive. We feel a cool sensation as the leaking air evaporates the water on our hand.

Another method for checking seal integrity at body openings, is using a strip of paper. A length of adding-machine paper works well for this task. Place the paper in the opening and close the door or trunk. When we have a good seal, pulling on the paper reveals a strong resistance. Paper that we can easily pull out with little force shows a potential leak spot. Correction may require adjusting the door or trunk to close tighter or replacing the seal.

With wrecked vehicles, distorted openings often prevent doors and trunks from sealing. Straightening or replacement of the body panels corrects the problem, though this may be out of the scope of home mechanics. Some collision repair shops provide this service.

Leaks at the door hinges

They design vehicles to direct water flow away from most openings. Rain and water from washing, flows over several components on the way to the ground. Components that attach through the body of the vehicle are potential leak points.

On newer vehicles, they often weld door hinges to the body. Older vehicles use bolts, that pass through the body. Sealing bolted on hinges to the vehicle body is necessary to prevent leaks. Doors sometimes get out of adjustment. To address the problem, they sometimes loosen door hinges to adjust for wear. This may break the original seal and create hard to find leak points.

Water runs down the cowl and hits the door hinges. If we have not sealed the hinge to the body, water enters and may run a distance before it shows up. Most often the water will puddle on the floor, though the leak is much higher, at the hinge pillar. Sealing the perimeter of the hinge with seam and body sealer often solves the problem. Auto parts’ stores normal carry a selection of body sealers that work well.

Leaks at the trunk and sunroof

Tail lamp fasteners often pass through the vehicle body. We must properly seal the tail lamp assembly to prevent water in the trunk. This often occurs after removing the tail lamp, perhaps to replace light bulbs. Water enters around the bolts that secure the lamp and often puddles in the lower recesses of the trunk. On some models, water runs forward and wets the rear floor.

Sunroof leaks

A factory installed sun-roof is well designed. The roof and glass rarely leak and most problems result from restricted drains. Channels on each side of the opening direct water to the drains. These drains run through the vehicle body and water comes out under the floor. Close inspection normally shows a small drain hole at the front and rear of the drain channels. Debris can plug these drains and cause the channels to overflow. Lightly applying compressed air will often clear the plugged drains.

Leaks around windshields

In modern vehicles they often glue the windshield in place; therefore, the windshield rarely leaks.  Replacement windshields are not always properly installed and leaks are possible. Testing a replacement windshield, soon after installation, is wise. Driving through a car wash does a good job of checking a windshield installation. Also be certain to have a clear understanding with the installer, concerning leaks that we do not recognize immediately.

With these simple tests the source of most water leaks can be found. Correction most often involves restoring the protection the manufacturer added during assembly of the vehicle.

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