WATER in vent plenums after heavy rain? [Archive] - Bimmerfest - BMW Forums

: WATER in vent plenums after heavy rain?

05-12-2010, 03:26 PM
I have searched and read several good threads on the musty a/c problem. I have at least that and plan to go under car and ensure that the drain tubes are not clogged. My issue seems to be also that if either driving in, or letting car sit in, a heavy rain, (with windows up and sunroof closed, of course) water collects somewhere deep in the system - never leaking out into the cabin or soaking carpets.

More info: I bought the car last fall and drove it home in a driving rainstorm for hundreds of miles. During that drive home I remember that the vents seemed to be putting out less and less air even with the fan settings on their highest... Getting in late that night, I let the car sit out in the driveway overnight in more heavy rain. The next morning it was clear out and rain had stopped. I heard a sloshing sound of water as I drove off. This sound was clear and the water seemed to be moving to and fro as I went into corners or sped up/slowed down. Within a few minutes that morning, the sloshing sound went away and my vents returned to normal function. I figured that the rain water overwhelmed the drains, and drained off, then I forgot about it - until now when more rain is here and warmer weather as well... I have yet to hear sloshing this spring after any rains, but I do have a slight musty smell that lasts just seconds on start-up.

So my question is - would clogged a/c evaporator box drains account for the water accumulating and subsequent sloshing as a result of rain fall and not just due to a/c operation? If not, is there a drain system I need to find for getting rain water out or keeping it out of the ventilation system? I did have the microfilters replaced as a part of dealer service I had done just a few days before I made that drive home... Could something have been put in wrong, allowing rain water to do this? I have to say that the fliters and their plenums under hood look properly installed to me...

I look forward to the imminent release of the Bentley manuals for the E60 cars - very soon...

05-19-2010, 03:43 PM
No one replied but here is what I have resolved so far... I carefully took apart the microfilter air boxes and plastic underhood panels. By the way, this is what you would have to do to access the brake fluid reservoir on the driver's side of our E-60 cars. I removed all these parts and examined the firewall area. There are water drains that go to each side a few inches forward of the firewall. Your microfilter boxes actually insert into rubber orifices that carry the water down through the fender where it drains out just behind the front wheels and around the fender splash guards. Both of my rubber fender water drains were storing quite a bit of pine needle and leaf debris. I found it easier to carefully pry out these drains from the inner fender to clear them. They feature a solid piece of rubber at their tips to restrain all that crap from falling lower into the fender area. After cleaning all that up and reassembling it all at least I can check that obstruction issue off the list. I am not sure that this would have really caused water to back up enough to pour over the air intake from the air microfilters - which would certainly result in water pouring directly into the center vent area past the a/c evaporator core - which you can see when you remove your microfilter boxes. Anyway, this is just an update as I work to reduce the problem. Maybe the next heavy rainstorm I drive through will prove this out or not...