Rusted rear footwell Mazda 6 MPS

[BaiJie90]

Hello,

So recently my Mazda dealer discovered a rusted through hole in my right rear footwell. They said it was quite an uncommon place to have rust starting there.
Is there like an underlying issue like leakage or was it some unfortunate event?

Please advice

See images:

 

[Raider]

That's pretty wild. Doesn't look like rust anywhere.

Perhaps it bottomed out and over time driving in rain just caused it to rust. Fast forward 17 years.

Can probably get a patch panel or cut a piece out at a wrecking yard and get it swapped out. Then spray a coating to prevent rust.

 

[SyntheticAtmosphere]

If you have a sunroof, it is possible a drain tube had plugged causing rainwater to leak into the car.
Also possible is the A/C system leaking due to a plugged HVAC case drain. Check to see if water flows out the drain tube on the firewall or try clearing it by shoving a piece of wire up if plugged. Or this related issue.
Pull up the front carpet at check to see if it shows signs of wetness or has a musty odour.
I had an issue with my A/C expansion valve freezing up and causing a small amount of water to soak the passenger floor carpet.
Also check the seams at the bottom corner of the rear window. The seam sealer cracks with age and can cause leaks.
I have had all these issues with cars over the years.

 

[BaiJie90]

If you have a sunroof, it is possible a drain tube had plugged causing rainwater to leak into the car.
Also possible is the A/C system leaking due to a plugged HVAC case drain. Check to see if water flows out the drain tube on the firewall or try clearing it by shoving a piece of wire up if plugged. Or this related issue.
Pull up the front carpet at check to see if it shows signs of wetness or has a musty odour.
I had an issue with my A/C expansion valve freezing up and causing a small amount of water to soak the passenger floor carpet.
Also check the seams at the bottom corner of the rear window. The seam sealer cracks with age and can cause leaks.
I have had all these issues with cars over the years.

I followed most of your suggetions, I have no sunroof so that one is rulled out. So there is water flowing out of the drain tube on the fire wall. Would it still be possible that it leaks in the cabin? It didn't feel wet or had an odour, but I might have to double check this.
Furthermore I don't see a connection from a leak in the front passenger seat to having rust at the rear, maybe you can elaborate more?

I still have to check for leaks at the rear window. And another question, will the carpet like show any signs of a leak, besides wetness? Like extra wear or something, or even a different color?

Thank you

 

[SyntheticAtmosphere]

I followed most of your suggetions, I have no sunroof so that one is rulled out. So there is water flowing out of the drain tube on the fire wall. Would it still be possible that it leaks in the cabin? It didn't feel wet or had an odour, but I might have to double check this.
Furthermore I don't see a connection from a leak in the front passenger seat to having rust at the rear, maybe you can elaborate more?

I still have to check for leaks at the rear window. And another question, will the carpet like show any signs of a leak, besides wetness? Like extra wear or something, or even a different color?

Thank you

I had an issue where the water would weep back from the drain outlet and soak the foam seal at the firewall. I then applied a zip tie to force the water to form a drip before reaching the firewall. If the drain is working properly, it should not drain into the interior. If plugged, it can fill up the bottom of the HVAC case and leak inside.

As for the water originating in the front, it can flow from the front to the rear. The reason the rust is at that place on the pan is because it couldnt flow any further.

The easies was to diagnose previous wetness is to look at the jute insulation backing. If kept dry it maintains it structure, but if its been wet it regularly sticks to the floor and comes apart in layers. You will also find rust under the asphalt melt sheet sound deadener. These might help you trace the water flow back to the source.

 

[BaiJie90]

I had an issue where the water would weep back from the drain outlet and soak the foam seal at the firewall. I then applied a zip tie to force the water to form a drip before reaching the firewall. If the drain is working properly, it should not drain into the interior. If plugged, it can fill up the bottom of the HVAC case and leak inside.

As for the water originating in the front, it can flow from the front to the rear. The reason the rust is at that place on the pan is because it couldnt flow any further.

The easies was to diagnose previous wetness is to look at the jute insulation backing. If kept dry it maintains it structure, but if its been wet it regularly sticks to the floor and comes apart in layers. You will also find rust under the asphalt melt sheet sound deadener. These might help you trace the water flow back to the source.

The carpet doesn't show any signs of previous lekkages. Furthermore the window doesn't seem to be leaking. Everything now kinda indicates it was just an unfortunate event.

Thanks for your input

 

[SyntheticAtmosphere]

I spent a number of years operating Stamping presses and in Die Maintenance I can shed some light on that as well...
Although it isnt common across a mass of vehicles, sometimes there is a flaw in the metal that can cause early corrosion issues affecting 1 or a small run of vehicles (depends on how good your Process Quality ppl are, or trackability). The metal can be compromised from the foundry. Also cracking, necking or folding can cause areas of concern. The exact area where you have an issue has 2 possible culprits. The way the metal is formed in a floor pan where there is a deep depression and a corner creates extreme pressures in the stamping die, if there isnt enough metal material you get cracking, too much and you get folding. Also there is a weld line where 2 panels meet. Issues with resistance welding lead to failures along seams resulting in early corrosion as well.
It is totally possible that you have an issue where its just pure bad luck. This is a caveat of mass production.
One of the worst die sets we had was for the A-pillars on the Toyota Sienna, we would throw parts directly into the scrap bin at the end of the press conveyor due to cracking regularly. Those dies had been crashed so many times they were impossible to repair. And we were one of the highest quality Honda/Toyota stamping and welding facilities in North America, lol

Luckily it looks like you have a lot of good material around the area a patch could be welded in and would be just as strong.