Typical 95-99 Monte Carlo/Lumina rust.
 

Anyone who knows anything about 95-99 MC's and Luminas know just about every one out there is rusted out under the fuel fill door. When I got my 98 LS, there wasn't one speck of anything. It was as clean as a whistle. But, over the course of last winter, I have gotten a few small bubbles. What caused these cars to all rust out like that? Does water get behind the fender via the fuel door? As anyone figured out a way to try to seal that up to try to prevent water from getting down there?

Talk, discuss, give advice :) ;)

Oh the joys of living in the south, mine is rust free. I have noticed that leaves and all that stuff tend to collect around the trunk weatherstripping, could be it? I noticed it when mine sat under trees for a few months, whenever i'd pop the trunk, there would be moisture.

Around the fuel filler, behind the sheetmetal of the quarter panel is foam insulation that holds moisture. That is the cause of the rust around the fuel door. Not much you can really do to prevent it.

I have looked up in mine and there is no foam :confused:

Maybe that's why it is still pretty nice yet...

Looked up in where? Open your trunk and pull the liner back on the drivers side. Stick your hand up along the inside of the quarter panel. You can feel the foam. If its not there, someone reached in and pulled out some of the foam. There is still some in there tho, I guaruntee it.

Mine doesn't have the rust, it DOES however, have paint coming off due to previous owners spilling gas.

I haven't found any kind of foam under mine whatsoever.

I looked with a flashlight and reached from underneath the car and saw nothing.

You cant get to it from underneath. Its behind the sheetmetal of the quarter panel. You can get to it from inside the trunk. Ill take a picture of it sometime tomorrow.

Okay, I think I found the foam you were talking about, but it still doesn't make sense to me. That foam is not close to the area. I'm talking about underneath the car, directly behind on the opposite side of the sheet metal where it's rusting. Theres nothing there to hold moisture...

When you said below the fuel fill door I just assumed that you meant well, under the fuel fill door. The W-bodies do rust out right below the fuel door quite often. Im not sure exactly what you are describing, but are you talking about right above the front corner of the bumper cover around the wheel well? I have fixed alot of rust in that area on alot of different vehicles. Dirt can sit up on the lip of the wheel well and collect moisture. I dont think there is a 100% seal in that area so I think moisture seeps in behind the metal and starts rusting it out. You can actually kind of get behind it through the trunk like with the fuel door opening. Its hard to get to it, but it is possible. I would spray some rust proofing down in there. You can buy it in an aerosol can and it comes with a little plastic straw. Spray it down in there as much as possible. Once it starts rusting tho, it wont do much more than just slowing the inevitable. Just be sure to keep inside the wheel well lip nice and clean too. That will help alot. I try and blast water in between my quarter panels and the bumper cover to keep dirt from accumulating in between the two. My quarters arent showing any signs of rust yet so I assume its working.