Warning: Rear frame rail rust due to bizarre engineering failure...
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#17
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Given how clean the interior of the body looks, I'd say that's classic entrapment corrosion. The body coatings that stiffen up (reminds me of the old Ziebart stuff) have a problem in where they are breached, water collects behind them and the corrosion process is accelerated in that area. It could be that the heat shields that are breaching the coating in that area. You might be better off not re-installing the heat shields or spacing them to stand off the panel a tiny bit.
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Given how clean the interior of the body looks, I'd say that's classic entrapment corrosion. The body coatings that stiffen up (reminds me of the old Ziebart stuff) have a problem in where they are breached, water collects behind them and the corrosion process is accelerated in that area. It could be that the heat shields that are breaching the coating in that area. You might be better off not re-installing the heat shields or spacing them to stand off the panel a tiny bit.
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Hi
I think that the issue is that the bumper/fender support plate was attached to the car before painting. This left a groove at the top in which water could collect (and a nice flat plate next to it for gathering water) and so porsche used a run of silicone or similar to seal the gap.
The quality of this sealant application was pretty variable and so some cars are fine and some aren't. It seems to be a particular issue with turbos, maybe due to the heat?
Once the water gets past this sealant and so between the support plate and the chassis, it finds unpainted metal which is why the corrosion is so bad.
The main problem is that it is hidden so most people won't know that they have the issue.
Steve
I think that the issue is that the bumper/fender support plate was attached to the car before painting. This left a groove at the top in which water could collect (and a nice flat plate next to it for gathering water) and so porsche used a run of silicone or similar to seal the gap.
The quality of this sealant application was pretty variable and so some cars are fine and some aren't. It seems to be a particular issue with turbos, maybe due to the heat?
Once the water gets past this sealant and so between the support plate and the chassis, it finds unpainted metal which is why the corrosion is so bad.
The main problem is that it is hidden so most people won't know that they have the issue.
Steve
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I crossposted on the 993 forum and they mentioned this link:
http://www.jackals-forge.com/lotus/9...issupports.htm
There are quite a few pictures in here that drive home how little the corrosion has to do with the heat shield.
This one in particular shows it pretty well, although unlike mine, it doesn't look like Porsche sealed it in to the same degree. (Which is probably why he didn't have nearly as much rust.)
#24
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Ah, the missing picture.
That stamping contains a nice channel to funnel water and dirt between it and the body. I think a small mod to that piece to let water pass out would be the best preventive solution. Doors are made this way with drain holes in the bottom.
That stamping contains a nice channel to funnel water and dirt between it and the body. I think a small mod to that piece to let water pass out would be the best preventive solution. Doors are made this way with drain holes in the bottom.
#25
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Sounds like we all need to take the rear bumper off our cars and have a little look and see just to be on the safe side and then do some painting and undercoating.
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Awsome thread with super pics. I'm not sure we need to worry about it Glenn. Our cars barely see rain and never salt. Also, that area of the body is so hot, I can't see how any water would last long enough to rust unless there's a bunch of dirt in there.
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I wonder how/if this should play into PPI's for future buyers and owners???