How to Repair a Leaking Windshield Sealby Brandon M. Dennis
Leaking windshields are, in most cases, caused by faulty seals around the glass, perhaps created by mildew or other deterioration of the rubber or the glue that holds it in place. Depending on the extent of the leakage, the driver may only notice the compromised seals during a rainstorm or while the car is being washed. A leaking windshield can cause water to accumulate on the dashboard, the headliner felt and even the carpet, which can allow mold to grow in the car. If the leak isn't severe, you can fix it in your driveway.
Rule Out Everything Else
There are four ways that water can leak into the interior of a vehicle: through a hole in the actual body of the car, a crack in the windshield, a faulty windshield seal or the air conditioning vents. While faulty windshield seals are usually the cause of a leaky windshield, do a quick look around to ensure that there isn't any obvious damage to the body itself or the windshield and also that water is not leaking into the interior of the car from the dashboard, since a faulty heater core can wet the carpet in the passenger compartment.
Checking the Windshield
Once you rule out all other sources, check the windshield seal for leaks. This can be done in a variety of ways, but the most common techniques use soap and a garden hose. Pour soapy water over the outside of the windshield around the trim while an assistant aims an air nozzle toward the edges of the windshield on the inside of the car. Look for bubbles around the edge of the windshield. The air causes bubbles to form in the soapy water at the leak. Another method is to turn a garden hose on the outside of the windshield around the trim starting at the bottom of the glass and slowly move higher as your assistant watches from the inside to see where the water starts coming in.
Sealing the Leak
Once you find the leak around the windshield, remove the exterior trim. Thoroughly clean the channel around and under the seal with an adhesive remover, such as paint thinner, rubbing alcohol or lighter fluid. Once you have removed the old sealant and washed and dried the area, apply new sealant directly to the windshield under the seal. If needed, apply sealant generously to the exterior of the seal as well, but don't allow it to run inside onto the dashboard or nearby accessories. Smooth rough areas with an index card to create a professional appearance, and trim the flash after it dries. Note the curing time on the sealant and allow it time to set.
Preventing Future Damage
Once you've repaired the windshield, perform the leak test a few more times over the next few days. If the leak persists or you are not confident in the repair, take it to a glass shop to perform the repair.
Brandon Dennis holds a bachelor's degree in mechanical engineering from the College of Central Florida with a minor in journalism. Since then, he has enjoyed working in the automotive aftermarket and has done so for the past six years. He is also currently seeking an ASE Certified Technician Certificate.