So frustrating! We had torrential rains here in Houston back in the spring and the trim piece that covers the fresh air plenum cover at the bottom of the windshield had cracked so with the heavy rain I had water leak into the car. I travel a lot so sometimes my car sits in the driveway for a month at a time. When I discovered the wet carpets and mold all over the upolestry I worked at cleaning it all up, drying out the carpets and padding and killing the mold spores. I found a commercial grade fungicide/mildewicide and really went to town wiping down everything several times. I put a couple of box fans at the doorways and ran them for several days until it all seemed dry.

Now we have had some more heavy rain (heck it's Houston!) and I find new mold growing from the humidity and the car had been left closed up for the past month. No water in the carpets since I replaced the lower and side finisher pieces after the last leak.

Any suggestions for something that might work better? I don't want to use bleach since it might cause damage. Tempted to spray vinegar as that is an old cure for mold.

 

So I'm in the real estate business, and buy up places to rent out.

Needless to say, I've become familiar with various and sundry odors/smells/mold/cats/****/smoke etc.

hands down, the best thing that will work on it is an ozone generator. I bought one for the last condo we acquired, which was a short sale formerly occupied by a camel-smoking cat lady.

This one on amazon did WONDERS.


It took a few treatments for the smoke to go away, and some cleaning, but bang for the buck, this little SOB did a great job.

Lots of info on ozone on the interwebs, you can look it up, but for killing off the mold and the smell, it does a hell of a good job.

I use it on my cars too, just wind up the timer and leave it on for 2 hours at night with the window cracked for the extension cord.

 

So you're sure it's coming in thru the windshield cowl? Make sure the drains on each side of the cowl area are clear of leaves/debris. Check your windshield gasket (clue that it probably leaks is if the windshield isn't OEM)... I have not had much luck with any aftermarket windshield installs and them being leak free. Sunroof drains are also another thing to check.

I'm in Beaumont, and before my garage/carport my D1/D2 sat out in the elements. I made sure they were parked as level as possible and that seemed to help the water drain naturally vs pool, collect, and leak.

 

I don't have any suggestions for sealing the car, but if you want to just keep it dry, I'd suggest buying a few buckets of Damp-Rid and leaving them in the car when you keep it sitting for awhile.

When I used to have mildew problems in my house, I would just leave a thing of Damp-Rid in a few rooms and by the end of a month or so it would be full of water which was moisture in the air.

 

Same thing happened to me after some rain here in SF. I didn't get any mold, so I can't help you there...
But I did find my leak: the top of the front door seals. I fixed it by applying a little bit of silicone based grease to the seal. So if you can pinpoint a bad seal (doors, sunroof, windows), grease does the trick. If your windshield is leaking, RTV works great for that.

 

Are you sure it's not the AC? Have you made sure the AC drains are clear — nipples underneath.

 

I don't think it's the AC drains. He said that he doesn't use the car and it may sit for months.

Get or borrow an ozone generator. They work great. Here;s one for $80
My blower drips when it rains. It has been doing this for a while. I need to find the source of the leak.