[Processing61]

My E91 has quite a bit of rust on both rear arches so I am going to get this sorted sooner rather than later. Can just see a couple of small paint bubbles appearing but on he inside of the arch it’s worse, but no holes.

I could be completely wrong but I can’t help but wonder if it’s partly to do with the carpets that are used on he rear arches (at least they are in the U.K. anyway). The carpets get wet, soggy, hold dirt and other crap and then it just sits agains the paint.

I was curious to know if it’s possible to get plastic liners like there are in the front? If I get it repaired I’m not keen putting the carpet arch liners back on again.

[Mike K]

Gotta photo of this?

[feuer]

That material is there to make the ride quiet. Noise and comfort always comes from the rear. So no, you can’t replace that with plastic. There are two types of material. Rough/coarse that traps more dirt. Found in entry level models. Also older models. Newer and high end models have smoother material. These chassis isn’t prone to rust. Probably at some point body repair was performed and metal wasn’t properly sealed.

[Processing61]

Originally Posted by Mike K

Gotta photo of this?

I’ll upload some a bit later on today

[Processing61]

Originally Posted by feuer

That material is there to make the ride quiet. Noise and comfort always comes from the rear. So no, you can’t replace that with plastic. There are two types of material. Rough/coarse that traps more dirt. Found in entry level models. Also older models. Newer and high end models have smoother material. These chassis isn’t prone to rust. Probably at some point body repair was performed and metal wasn’t properly sealed.

Ahh ok, that makes sense. I might see if I can get some new carpet liners just for peace of mind.

I thought these were a bit prone to rust in certain places? I thought in general E9X series were prone mainly on the rear subframe but spreads to the underbody of the car, especially at the rear. but not so common in the actual arches. Then on the E91 extra places like tailgate sides rusting and top of boot/tailgate.

It looks like the factory rust prevention coating and weld sealer but I could be wrong. In the U.K. it rains a lot and we often use road salt so I think that speeds the process up

[feuer]

Originally Posted by Processing61

Ahh ok, that makes sense. I might see if I can get some new carpet liners just for peace of mind.

I thought these were a bit prone to rust in certain places? I thought in general E9X series were prone mainly on the rear subframe but spreads to the underbody of the car, especially at the rear. but not so common in the actual arches. Then on the E91 extra places like tailgate sides rusting and top of boot/tailgate.

It looks like the factory rust prevention coating and weld sealer but I could be wrong. In the U.K. it rains a lot and we often use road salt so I think that speeds the process up

Absolutely no chance of rust on subframe to transfer to wheel arches. I’m in IL. Rain and salt too. No rust. If the vehicle was repaired, maybe was never properly washed, had over sized tires that rubbed on the arches, that would have cause it.

[Processing61]

Originally Posted by feuer

Absolutely no chance of rust on subframe to transfer to wheel arches. I’m in IL. Rain and salt too. No rust. If the vehicle was repaired, maybe was never properly washed, had over sized tires that rubbed on the arches, that would have cause it.

No, I meant rust on the subframe transferring onto the underbody of the car, on top/underneath where the subframe/rear axle is. Where the rear axle/subframe mounts on the bottom of the car, that's what I was saying in the last message, not about transferring from there to the wheel arches.

Yeah regarding the arches I think never washed properly would be a good shout. I've only had the car for 4 months and I stripped all the panels off to see how bad the rust was and at the edge of the arch liner and quite far down behind the arch liner there was so much wet dirt and debris just sitting in between the liner and the arch, on the metal, rusting it away. Same again when i took the side skirts off and the panel around the bottom of the side skirts. It has done 198k miles too.

[feuer]

Originally Posted by Processing61

No, I meant rust on the subframe transferring onto the underbody of the car, on top/underneath where the subframe/rear axle is. Where the rear axle/subframe mounts on the bottom of the car, that's what I was saying in the last message, not about transferring from there to the wheel arches.

Yeah regarding the arches I think never washed properly would be a good shout. I've only had the car for 4 months and I stripped all the panels off to see how bad the rust was and at the edge of the arch liner and quite far down behind the arch liner there was so much wet dirt and debris just sitting in between the liner and the arch, on the metal, rusting it away. Same again when i took the side skirts off and the panel around the bottom of the side skirts. It has done 198k miles too.

Mileage has nothing to do with it.

[e90yyc]

I’ve got a tinnny bit of bubbling in my front arch. It sucks because yes: these cars are very well protected from rust, and even with the harsh climate and use of road salt where I live, most older BMWs I see still look great. Not sure what gives in my case… There was no previous accident repair, but I’ll take a look later and see if I can find any indication of broken paint/bent metal inside the arch where the metal is rolled.

My back arches have been fine though. I’m also curious to see these pics. Having “a lot” of rust anywhere on the body of these cars strikes me as unusual.

[Mike K]

After I bought my e91 last spring, I pulled out all the wheel arches liners, all eight and pressure washed a TON of crap out of each corner. My car came from South Carolina and was perfectly rust free, yet there was red clay dust packed behind the arch liners. I even had tiny SC ants living in under these! There must be some law about transferring ants across state lines SC to the Chicago area!

It was along weekend job and pretty thankless laying in that wet crud but I’m sure glad I did it! I really couldn’t believe how much was packed behind the wheel arch liners.

[Processing61]

Originally Posted by feuer

Mileage has nothing to do with it.

Really? I would have thought if there was wet dirt and debris sitting against the paint/metal, surely the more miles the car has done, the more time the crap/dirt has been there for increasing the chance of this turning into a problem, like causing rust?

[Processing61]

So ive uploaded some pictures here with most of the places I have found rust https://postimg.cc/gallery/x8TprL8

Both rear arches, the outside panel is a bit harder to see but you should see some bubbling. Internal rear arches. Bottom of battery tray, along with both frame rails/rocker panels/side panels (not sure what they are called) and one area actually has a hole which I will need to get a new bit of plate welded (puts me off as it's near a jacking point), both sides of the boot/tailgate (haven't got a picture with the trim off yet). The front arches have a bit of bubbling too but I don't have any pics of that. Also in general the rear subframe/axle does look quite corroded, might be more surface rust.

The front subframe/axle looks so clean comparing them both, I guess that's as it is Ally rather than some kind of Steel on the rear

[feuer]

Originally Posted by Processing61

Really? I would have thought if there was wet dirt and debris sitting against the paint/metal, surely the more miles the car has done, the more time the crap/dirt has been there for increasing the chance of this turning into a problem, like causing rust?

Being stationary would have made it worse when these areas would be packed with debris already. The mileage itself isn’t a big factor here. Where it was driven, like: wet, dirt, salty roads and maintenance are the biggest contributors. Ready previous post #10 The arches, at least one, shows imperfections, the edge isn’t even, so I assume has been resprayed. These quarter panes are clued to the Inner wheel liner. The sealer is already separated in places along the arch. Debris, water, salt would not cause the sealer to separate like that. Being separated would explain the rust in the rocket panel. I see you already agitated the rusty spots. When you start doing the same on the outside body you will know for sure if some type of repair has been done. I suspect yes.

[Processing61]

Originally Posted by feuer

Being stationary would have made it worse when these areas would be packed with debris already. The mileage itself isn’t a big factor here. Where it was driven, like: wet, dirt, salty roads and maintenance are the biggest contributors. Ready previous post #10 The arches, at least one, shows imperfections, the edge isn’t even, so I assume has been resprayed. These quarter panes are clued to the Inner wheel liner. The sealer is already separated in places along the arch. Debris, water, salt would not cause the sealer to separate like that. Being separated would explain the rust in the rocket panel. I see you already agitated the rusty spots. When you start doing the same on the outside body you will know for sure if some type of repair has been done. I suspect yes.

Ahh ok, well thanks for all the info!

Yes with the rocker panel I tried removing most of the rust, treating with rust converter and then painting, just to try and slow the process down a bit. But I will get the hole repaired as I don’t know how to weld.

Where the sealer or rust protector coating was I noticed that I kind of seemed like it failed. So if I sanded or chipped back the sealer/rust protection coating it would be moist underneath and have a lot of surface rust. I noticed this too along the rocker panel where the punch weld is, if I removed the sealer/rust coating where the punch weld is, it would be a little damp underneath and have surface rust, almost like it’s attracting and sealing in moisture rather than protecting it, like it’s failed.

Could this be due to mileage and the factory sealer/rust protection coating failing over a certain period of time/mileage? Or would this mean a previous repair too?

Just as there is quite a bit of rust in various places I wouldn’t have thought that all these areas have had some kind of previous repair work

[Processing61]

Originally Posted by Mike K

After I bought my e91 last spring, I pulled out all the wheel arches liners, all eight and pressure washed a TON of crap out of each corner. My car came from South Carolina and was perfectly rust free, yet there was red clay dust packed behind the arch liners. I even had tiny SC ants living in under these! There must be some law about transferring ants across state lines SC to the Chicago area!

It was along weekend job and pretty thankless laying in that wet crud but I’m sure glad I did it! I really couldn’t believe how much was packed behind the wheel arch liners.

That does sounds like a dirty job!

Nice peace of mind though to know you have done it. I was also very surprised at how much crap there was, even behind the side skirts