Inner Trunk Seam Rust

[3800series2]

I tried looking in different 3800 forums regarding this but came up dry with exactly what I was looking for. I was doing a once-over of our 2003 LeSabre Limited and checking under the mats of the floor including the trunk for water or wet spots as I normally do since I have experienced wet floors in a couple of my cars especially the two Bonnevilles I owned. This came as a surprise to me when I noticed that the trunk mat was frozen to the trunk floor. Sure enough it was soaked and saturated with water on the left side. I pulled out all the carpeting and insulation in the trunk and noticed what you see in the picture attached. Has anyone experienced this or have an idea what caused this? The car has under 90,000 MI and has been reasonably maintained. The underbody is in good shape for a northern car that's 17 years old but isn't without rust. Cheers!

 

[broke_collegekid]

If you've got rust there I would check out your two rear spring perches in the wheel wells. You need to take the wheel off to have a look if you're able to do that. Those could be rusting too due to a poor design and if they rust through your rear springs could get unseated which is a mess.

I know I got a little rust like this too so I'm gonna stay tuned to see what people say

 

[HotZ28]

Those seam seals look something my 4-yr old grandson would do! GM should have fired the person for that abortion of sealer application. I could have done a lot better job drunk! Once you have rust at all those seams, you have little choice, except to reseal all the joints and spray a rust inhibitor (Por-15) on top & bottom. I wish you the best of luck!

Rust Preventive Coating

POR-15® Rust Preventive Coating stops rust permanently with a tough seal that resists water, chemicals, and corrosion. Protect your metal surfaces today!

www.por15.com

 

[broke_collegekid]

Those seam seals look something my 4-yr old grandson would do! GM should have fired the person for that abortion of sealer application. I could have done a lot better job drunk! Once you have rust at all those seams, you have little choice, except to reseal all the joints and spray a rust inhibitor (Por-15) on top & bottom. I wish you the best of luck!

Rust Preventive Coating

POR-15® Rust Preventive Coating stops rust permanently with a tough seal that resists water, chemicals, and corrosion. Protect your metal surfaces today!

www.por15.com

Mine is like that too minus the rust for the most part being all over. What I’m wondering is why they don’t just weld it

 

[Ultra Ego]

I agree with Z28, POR-15 is a good solution. However, you are only seeing part of the rust. To stem the rust progress permanently, you’ve got to do the following steps:

1) Find the source of the moisture, water getting into you trunk. Could be from the top, or bottom, or both.
2) Remove the existing sealer using a screwdriver, putty knife, chisel, etc., to expose the rust under the edges of the sealer you can’t see right now.
3) Descale the rust and paint over it with POR-15. When that dries, spray over the POR with a good quality paint, like Rustoleum, to seal it.
4) Recaulk the seams with a good quality latex caulk. Do not use silicone caulk! It pushes moisture to the outside edges of the bead, and you’ll be right back where you started from.
5) Spray paint over the caulk to seal it and give it more durability.

It is tedious work but it results in one area you won’t have problems with in the future.

 

[BuickGirlFromMars]

Mine is like that too minus the rust for the most part being all over. What I’m wondering is why they don’t just weld it

Seams the meeting points between the end of sheet metal and whereever it lays. the welding is all over and holds the car together, but the seams overlap and fall in different spots. seam sealer keeps moisture and dirt/debris out and help deaden noise

 

[BuickGirlFromMars]

Ive got similar damage in my park avenue on the same side. it was caused by a carpet that got soaked and probably a chip in the paint or something and the carpet held water against the metal and it spiraled. I dried it up, sanded it, and hit it with rust converter but its gonna eventually structurally give out underneath the car. im gonna ride it till it dies but its sad i wish i could have intervened earlier

 

[3800series2]

Thanks for elaborating y'all. This definitely appears to be a "made on a Friday" situation. However, is it possible that the site of the severe rust isn't the source of the water and just where it pooled? The mat was only wet on that left side where the rust is worst. I'm going to leave the trunk gutted for some time to provide open air and possibly see where water enters. I do plan to remove the old sealant, remove loose rust with a brush, hit it with VHT Rust Converter, possibly self-etch primer and paint, then seal back up. As for the wheel arches, I have been pretty good at reapplying undercoating as it chips in the rear wells. It is still possible I didn't see a corroded area, though. The car also isn't exhibiting the notorious gas cap area rust yet. I plan to brush and hit the bottom of the car with rust converter late spring. Just the average surface rust so far. Most of it under the plastic rockers that I've removed before and treated. Car has had a good wash regimen as well, especially in winter when temps above freezing. Always with undercarriage blast. Cheers!

 

[BuickGirlFromMars]

Thanks for elaborating y'all. This definitely appears to be a "made on a Friday" situation. However, is it possible that the site of the severe rust isn't the source of the water and just where it pooled? The mat was only wet on that left side where the rust is worst. I'm going to leave the trunk gutted for some time to provide open air and possibly see where water enters. I do plan to remove the old sealant, remove loose rust with a brush, hit it with VHT Rust Converter, possibly self-etch primer and paint, then seal back up. As for the wheel arches, I have been pretty good at reapplying undercoating as it chips in the rear wells. It is still possible I didn't see a corroded area, though. The car also isn't exhibiting the notorious gas cap area rust yet. I plan to brush and hit the bottom of the car with rust converter late spring. Just the average surface rust so far. Most of it under the plastic rockers that I've removed before and treated. Car has had a good wash regimen as well, especially in winter when temps above freezing. Always with undercarriage blast. Cheers!

have you verified your window reveal molding, urethane sealant, trunk seal, trunk gutter seams, and gutters are clear of debris and good?

this is of Park Avenue models but the exact same system is used in the 2000+ lesabre trunk lid sealing setup, so here is some service info its only a minute or so long on just the trunk area

edit: i pasted it at the time in the video where he demonstrates the trunk for your convenience

 

[RazMalibu]

I have a 2001 and 2002 LeSabre and my 2002 developed a leak in the trunk. I had not used it for awhile and was surprised to see the spare tire cavity nearly full of water after a couple of heavy rain storms. I drilled a hole in the bottom of the cavity to drain the water.

It took a while to find the leak. The water was coming in through a small hole in the sealant above the left taillight. I originally thought that it might be the seal around the trunk. I swapped the one from the 2001 to the 2002 and it still leaked. I had pulled out all of the carpeting and panels so it was down to the metal and easier to see the source of the water. No problems with rust as i caught it shortly after the leak started.

The metal is spot welded during manufacture and there are overlapping seams where the two pieces are joined. Then a mastic type of sealant was applied on the top of this joint as well in the interior of the trunk. The sealant had dried out and cracked. The mastic sealant was scraped to remove any loose pieces to make a good seal. The original mastic sealant is painted on and dries hard. This is great until it finally cracks and causes a leak.

There are a number of sealants available to seal this joint. There is a GM branded sealant that is available in body shop supply sources as well as Amazon. I used the Custom Shop polyurethane seam sealant adhesive compound purchased from Amazon. This one was readily available and not too expensive, it was less than $15.00 for one tube. This is more than needed to seal the seams on both side of the trunk on both of my cars. I let it dry for a day before another rain test and it was dry after a regular rain storm.
I hope that this information will be helpful in case this is a recurring problem

 

[BuickGirlFromMars]

I have a 2001 and 2002 LeSabre and my 2002 developed a leak in the trunk. I had not used it for awhile and was surprised to see the spare tire cavity nearly full of water after a couple of heavy rain storms. I drilled a hole in the bottom of the cavity to drain the water.

It took a while to find the leak. The water was coming in through a small hole in the sealant above the left taillight. I originally thought that it might be the seal around the trunk. I swapped the one from the 2001 to the 2002 and it still leaked. I had pulled out all of the carpeting and panels so it was down to the metal and easier to see the source of the water. No problems with rust as i caught it shortly after the leak started.

The metal is spot welded during manufacture and there are overlapping seams where the two pieces are joined. Then a mastic type of sealant was applied on the top of this joint as well in the interior of the trunk. The sealant had dried out and cracked. The mastic sealant was scraped to remove any loose pieces to make a good seal. The original mastic sealant is painted on and dries hard. This is great until it finally cracks and causes a leak.

There are a number of sealants available to seal this joint. There is a GM branded sealant that is available in body shop supply sources as well as Amazon. I used the Custom Shop polyurethane seam sealant adhesive compound purchased from Amazon. This one was readily available and not too expensive, it was less than $15.00 for one tube. This is more than needed to seal the seams on both side of the trunk on both of my cars. I let it dry for a day before another rain test and it was dry after a regular rain storm.
I hope that this information will be helpful in case this is a recurring problem

I had water fill my spare tire well from a PUNCTURE in the trunk floor that must have been an object projectile that pierced the floor and hit the trunk lid and went through the felt and dented the trunk in that spot. I couldnt locate a projectile that did it but holy cow. I pounded the metal back into spot and used a spot patch after spraying it with a paint