As temperatures have gotten colder, I’ve noticed a lot of condensation on the inside of the Leon’s windows. Today I did a bit of poking around and, to my dismay, discovered the carpet in the passenger’s footwell was soaking wet, and damp in the nearside rear footwell. This is not the type of thing you want to find, because it inevitably means doing what you see below to try and find the source of the leak.
The first thing I checked was the heater matrix behind the glovebox, but that seemed fine, and the carpet right behind that was dry. Additionally, there were no signs of leaking coolant, and the car wasn’t overheating at all (quite the opposite, in fact; I’ve just replaced a thermostat that was stuck open. More on that later.) The next thing to check was the water passages on that side of the car, and here I began to turn up some possible answers. First examining where the pollen filter sits, I immediately spotted a problem. The water channel adjacent to the pollen filter housing was blocked, and the filter itself was wet.
After cleaning that out, I followed the channel down to where it is supposed to drain, and found a huge buildup of mud and debris. Momentarily running water down the channel to see what would happen, it seemed possible that the blockage was redirecting water at the door seals, thus causing a buildup of excess water that was being forced under the trim on the door sills and into the car.
Removing the debris seemed to make the water run much more freely, and only flow where it was supposed to. It’s hard to believe just how much stuff was built up in there.
Whether this fixes the problem remains to be seen; I’m getting the carpets and damping material dried out today and tomorrow, so obviously won’t know for sure until I start with a dry car. A bit of Googling suggests that the door seals might also be the problem (which happily appears to be a relatively simple fix), and that will be the next port of call if this hasn’t solved it.