Hey everyone, I recently replaced the rusted trunk pan on my track car and I figured I would document the experience so that anyone who wants to do the same in the future could learn from my experience. I am by no means a mechanic and didn't really have any idea what I was doing. I wasn't able to find any documentation about this procedure in the service manual.


When I purchased this car a year ago in Tennessee I made the mistake of not inspecting the trunk for water damage. Months later when I dug into the trunk to get the tow hook for a track day I found that the spare tire kit was completely soaked with water. I stripped away the trunk carpeting to access the damage and found that the bottom of the pan had some pretty serious rust. After searching on s2ki I discovered that I would probably have to cut out the rusted pan and weld in a piece of sheet metal or replace the trunk pan entirely. Luckily, the trunk pan is sold as an OEM piece.

I picked up a new OEM trunk pan (65517-S2A-A01ZZ) for $125 along with some new drain plugs (91611-SM4-003).



After getting some expensive ($1200) quotes to have the new OEM trunk pan installed I decided to do it myself...

In order to get full access access to the trunk I had to remove the rear bumper, the exhaust, the rear swaybar bushings, and the rear crash beam. I won't go into detail about how to do these since they are all pretty straightforward and well documented on s2ki. The only one that might not be documented is the rear crash beam, which is 5 bolts that can be removed with a 12mm socket.



Once I had access to the trunk pan I tried to figure out how the trunk pan was actually attached to the body of the car. I used a heat gun and a wire wheel to remove the rubbery white seam sealer that covered in inside of the trunk pan and the rubbery black undercoating that covered the bottom of the trunk pan. The heat helped to loosen the coating and was easily removed with the wire wheel.
After struggling for quite a bit I found that there were a couple tack welds on the inside of the trunk pan in each corner. On the outside of the trunk pan I found several spot welds lining each side of the trunk pan. They looked like circular dimples in the metal that were evenly spaced out.







I drilled out most of these spot welds using a special spot weld drill bit. Originally I drilled directly through the trunk pan and the frame using a drill before learning about the correct tool to use. These spot welds line each side of the trunk pan. The forward most side, the left, and the right all need to be drilled out from the outside. The rear most side needs to be drilled out from the inside.
Once all the spot welds were drilled out I had to use an angle grinder to remove the tack welds from inside the trunk pan. Finally after several hours I removed the rusted trunk pan from the car.

After inspecting the way the spot welds were done I came to the conclusion that spot welding was not an option for reassembly. It looks like the way the spot welds were performed they were done on the assembly line as layers of the car were stacked on top of each other. I had no access to the interior of the frame rail. I devised a plan to weld the trunk pan to the frame from the inside. I figured the trunk pan could be tack welded to the frame from the inside. I found a mobile welder on craiglist who came to my house and 200$ later the trunk pan was welded to the frame. It wasn’t the most beautiful job and there were some blowouts but it was good enough for me since it was welded securely in place.



Now all that was left was to protect the trunk from future rust issues. The first thing I did was install two new OEM trunk pan drain plugs.
Next, I did my best to restore the OEM rubber underbody coating. I sprayed two cans of 3M professional grade rubberized undercoating on the underside of the trunk pan and where it met the frame. The spray came out really thick and left a nice textured black coat on the car. These cans set me back 18$ each.
Here is how it looked after a single liberal coating. If I lived in an area with more rain and snow I would probably use more cans and do even more coats but the car now lives in sunny California!



While doing research about the trunk rust issue I learned about a product called POR-15, aka paint over rust. After several recommendations, including Billman’s, I knew this was the stuff I was going to use to coat the inside of the trunk pan. I ended up buying the POR-15 starter kit for about 20$ which includes some paint, a brush, and preparation materials. I followed the instructions and prepared the work area before applying 3 coats of POR-15. It was extremely easy to apply with the brush and cured into an extremely hard gloss black protective coating.



The last I had to do was try to restore the OEM seam sealer on the inside of the trunk pan where the trunk pan meets the frame of the car. I picked up some seam sealer on Amazon for 14$ and got a caulking gun to apply it. After pushing out the seam sealer with the caulking gun I used my fingers to spread the sealer evenly along the gap between the trunk pan and the frame rail. My advice is so use the seam sealer sparingly and keep the layer as thin as possible to ensure that it will cure fast and harden. In hindsight I definitely applied too much seam sealer and could have been more careful.





And that is how I replaced my trunk pan. I made a few mistakes along the way but I saved myself hundreds of dollars and learned more about cars and the S2000 in the process so it's a win in my book. If you have any recommendations for ways that I could have improved this job please feel free to leave a comment for the benefit of others.

 

Looks good actually, good work!

 

And look, no sound deadening material to remove.

 

Nice work, great video as usual. Trunk leaks in s2000s seem to be pretty common -- I've had a few over the years in my AP1 and I see a *little* bit of rust on mine (certainly not enough for me to replace it).

I see you have a hardtop, and most of these leaks come from soft top usage, but I'd make sure yours isn't coming through the quarter panel (like mine) -- that little rectangular exterior piece adjacent the trunk lid sometimes leaks (and can be caulked).

Was yours rusted all the way through? E.g. Was it beyond sanding the interior surface rust and respraying the inside with POR?

Questions:

1. Since you got a closer look at the new rubber drain plugs -- they don't have holes in them right? I made a few small holes in mine.
2. Does the CR not come with a sound deadening pad? My AP1 has one -- I assume it's similar to this guy: https://multimedia.3m.com/mws/media/.../tds-08840.pdf (available here: https://www.napaonline.com/en/p/MMM08840)

 

Yes, it seems you still didn't address root cause. What let water into trunk in the first place?

If you don't find and fix that, you're going to end up with more water in trunk. The por15 will prevent it from rusting again. But you're still prone to mold and other issues.

Big thanks to taking this on, and especially for posting in such detail for the good of the community!

 

It is true I haven't figured out the root cause yet. I purchased the car with water in the boot and brought it to California. Since the car is garaged and mostly used for HPDE I'll have to go out of my way to spray water at the car and reproduce another leak. It's not exactly high on my priority list :P

 

As posted above, not sure where the leak is from and whether I'll even find it. Mine was definitely rusted through, I had a separate hole entirely due to rust that was hard to see on the video.
The new rubber drain plugs do not have holes in them but somehow they allow water to pass through. Didn't take a hard look at them.
I was sort of surprised about the sound deadening as well. I doubt the sound deadening was removed by the previous owner so it probably does not have any. My AP1 does have the sound deadening in the trunk.

 

 

There are specialised autobody caulking gun applied sealants that are alternatives to welding. These offer extreme holding power to bond metal to metal.

As much as I use and am impressed by jb weld, I don't know if its suitable for such an application.