In the last two weeks it has rained twice. Both times the floor and the floor only of my 99 Bonneville has been soaked the next day. I looked under the car and it seems that most of the underbody has a metal sheeth covering it, but there is a maybe 3 inch by 2 inch opening in the underbody. In that opening, the actual underbody is rusted. I imagine that the water is getting in through there. I am planning to jack the car up tonight, scrub the loose rust off with a wire brush, and load the hole up with caulk. Any other suggestions? Has anyone had experience with this?

We've seen sunroof drain issue, trunk leak issues...many other leak issue.

You have a hole in your floor though? Seal it up and that will probably fix the problem.

If the hole in the floor doesnt fix it, then try looking at the drivers side rear door moulding. Mine used to get soaked and it ended up being due to shrunken door moulding in the rear.


Good luck!!

Hopefully, the floor rust is really your problem. If not, stick with it. Experience here indicates that leak issues can be a PITA to locate and resolve, but resolve them you must or you will end up with other issues. Besides mushrooms, you risk electrical issues, etc.

Best advice is to stick to it until you get it resolved.

Does the water only appear after driving? Is the car in a garage or something when not being driven?

If it gets wet while being parked outside it'* your door seals leaking. I've had to reseat all of mine and add a chunk of rubber at the bottom due to shrinkage. It stopped all of my leaks, however, mine weren't as bad as you describe.

The car is unfortunately outside. We don't have a garage. It has only happened twice now. I will caulk the rust hole and check the door moulding. Thanks for all the replies, you guys are great!

I'm really not sure whether it gets wet when it rains or just when I drive it after it rains. It has only happened twice. I went over all the door seals with a fine tooth comb and they all look fine. I also jacked up the car, and I don't think the small rusted areas on the undercarriage are actually reaching the interior. I pulled up the sound proofing and carpet in the back and there was a puddle of water down there. I had to shop vac it out. If the hole was in the floor, wouldn't the water drain out?

I'd re-examine the door seals. Especially at the top corners where the seal goes to, then down along the B-pillar (middle support "arm"). That'* a VERY common spot for the seals to become unseated from the rail they're mated to.

there supost to be a hole in the floor. just like you said for water to drain out if ever or when ever water gets in there.. and the moding around the door some times give out and some time it looks good to ... but did you ever had the a windos replace?