A car window doesn't offer much protection if the window seal is loose or cracking. Sure, most of the wind will be kept of your car while you are driving, but even a small crack or slightly loose seal can let water into your car. If this leak goes unnoticed, you can end up with unsightly water damage to your interior. Fortunately, most cracks and loose car window seals can be glued with polyurethane caulking. Add some of this caulking to your broken seal, and you should have your window back in tip-top condition in minutes.
Spray your car window with a little water from your hose. This will give you an idea of how large the crack is or how much of the seal is loose. This is an important step because the extent of the damage might not be fully visible to the eye. You do not want to complete the repair job only to find that you did not fix the entire problem.
Use a towel to clean off the window seal area you are going to repair. You can use a little water if you find a lot of dirt and dust. It is important to make sure the entire area is clean before you apply the polyurethane caulking. Dirt and dust will compromise its adhesive bond.
Use sand paper to create a rough surface on the part of the window seal you will be caulking. Polyurethane caulking will need a rough surface to create a strong bond.
Hold the polyurethane caulking bottle at a 45-degree angle and apply to the cracked window seal or apply to the top of the seal if it is loose and out of place. Holding the bottle at 45 degrees will help ensure an even application of caulking material to the window seal.
Hold the window seal in place if the seal was loose and out of place. You can let go once the caulking has dried enough to hold the window seal in place.
Test your glued window seal only after the caulking has completely dried. Read the back of the caulking bottle to find out how long it takes for the caulk to dry because there may be a slight variation depending on the brand you're using. Once the caulking is dried and your window seal is glued in place, there should be no more leaks.