Renault Megane 2007 | Part 2 | Water Leaks Found Video

Question: "Why are you putting those bars down the window? Aren't you just creating a leak where there wasn't one before?"

Answer: The outside of the window does have a rubber seal on it and this will deflect most of the water and prevent it from going inside the doors, but some water always gets past this. Most will run down to the bottom of the door where it can flow out through drainage holes. There's a plastic membrane which is another barrier preventing water getting inside the car, but this isn't a submarine quality waterproof seal. You often find that cars are designed in such a way as there are multiple weak barriers which deflect water away to a place where it can escape. Water leaks are typically caused by a number of factors, an outer rubber not as tight as it was, inner seals shrinking, and drainage holes blocked. Then, if you get a particularly heavy rain, they all get overwhelmed.