E30 Vert Floor Rust

[dcover7]

My floor panels up front are all rusted out. I believe I found the cause for the passenger side, a drain plug was missing allowing water soak the carpets while driving in the rain, the rocker drain was blocked up with about a liter of water, and the "elephant drain" was plugged. However, on the driver side only a square section is rusted right underneath the pedals. Any idea what would cause this rust? In the attached picture, I have since removed all that sound deadening crap. It is only rusted in that area on the picture. Thanks for the help!

[dnguyen1963]

Heater core is the only thing would would leak in that area, I think.

[e304lyfe]

water coming in from heater box area, also check higher up on firewall for rust. potentially coming in from fuse box area or the air intake for heater box (exposed vent holes where wiper attaches).

spray a lot of water outside and drive through some decent rain showers with the carpet out until you find all sources before you put the carpet back in. definitely take your time to isolate all sources for a leak, as they can be tricky to find.

[dcover7]

Ok, thanks for the info. If it's the heater core would I see coolant coming down the trans tunnel when I have the heat on? I'm about to patch the rusted areas and don't want it to rust all over again!

[roguetoaster]

The heater core normally just seeps coolant, and usually under/through the carpet. Generally you can't see it running, but the moisture accumulates slowly.