Dry the area, close the door with you inside the car, then have a helper spray water on the door and window. As soon as you see water running in, open the door and look for the highest point you see water on the weatherstrip. If the water seems to only come in while you are driving, look at all the little holes in the weatherstrip and be sure they are not plugged with debris. Air is supposed to get in them to make the weatherstrip expand so it seals better. If there is a section that is deformed to the point it will not seal, you can cut a slit in it, then slide in a piece of vacuum hose. Also, look at the front edge of the door to be sure it is not sticking out further than the rear edge of the fender.
There is a special tool to tell if there is a gap preventing the weatherstrip from sealing. That is a dollar bill. Stick it between the door and weatherstrip, then tug on it to see how hard it is to move it or pull it out. If there is a gap, it will slide out easily. If it is sealing properly, you will feel a drag on the "tool".
Dealer's parts departments have a white leak-locating powder in a spray can. It is basically talcum powder. Spray it lightly on the sealing area of the door opening, then close and fully latch the door slowly. Slamming the door like normal is too hard as it will compress the weatherstrip, then bounce back. Close it real slowly, then open it and look for any place the powder did not transfer to the weatherstrip. The door might be misadjusted or the weatherstrip could be deformed.
Wednesday, July 12th, 2017 AT 9:48 PM