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BMW 3-Series (E90 E92) Forum > BMW E90/E92/E93 3-series General Forums > General E90 Sedan / E91 Wagon / E92 Coupe / E93 Cabrio > E90 Rust Risk



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      06-03-2009, 09:18 PM   #1
3lusive
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E90 Rust Risk

My right rear jack support box on the undercarraige of the E90 fell off, and there is exposed metal "above" the empty space where the box used to be. I just drove thru a flash thunderstorm with tons of rain, is there a high chance that the car could rust at this spot?
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      06-03-2009, 09:23 PM   #2
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Quote:
Originally Posted by 3lusive View Post
My right rear jack support box on the undercarraige of the E90 fell off, and there is exposed metal "above" the empty space where the box used to be. I just drove thru a flash thunderstorm with tons of rain, is there a high chance that the car could rust at this spot?
None. It is galvanized steel. Get a new lift point.
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      06-03-2009, 09:35 PM   #3
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Galvanized steel doesn't mean it's mixed into the steel. If that area's been damaged in any way by the jack and you see dark grey or red (exposed steel or rusted steel) or if you're just worried you can buy some zinc-rich paint and spray the area. You'll need to clean the area with a wire brush and then spray on. Make sure you mask the area appropriately (I like to use two layers of white garbage bags and painters tape when doing any paint work on my cars).

As an aside, this is the same method we use for repairing bridge structures if the galvanizing is ever damaged or questionable and exposed.
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      06-04-2009, 12:37 AM   #4
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I don't think that 3 series body is galvanised. In all the Swedish rust proof reports the only cars that they mention as having total body galvanising are Volkswagen -Audi group. I think that the BMWs are just dipped in the primer. But I could be wrong and will be happy if I am proved wrong in this case!
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      06-04-2009, 01:50 AM   #5
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Quote:
Originally Posted by raj55 View Post
I don't think that 3 series body is galvanised. In all the Swedish rust proof reports the only cars that they mention as having total body galvanising are Volkswagen -Audi group. I think that the BMWs are just dipped in the primer. But I could be wrong and will be happy if I am proved wrong in this case!
Good catch, BMW does a cathodic dipped primer instaed of galvanizing. The paint doesn't have sacrificial anode properties like the zinc. However, even galvanizing will rust if the galvanized layer is scratched.

With cathodic dipped painting, it ensures that every piece exposed to air or water will be sealed with paint.

I had to check here to remember: http://www.bmw-plant-munich.com
(section Paint Shop in the Virtual Tour section)

But going back to the original question, if the exposed part where the plastic jack was got scratched or damaged, then it would rust since it's just paint. If it was galvanized, it would do better because of neighboring zinc will act as a sacrificial anode but all galvanizing will cease to work after a while. Even with galvanizing, it rusts after a while and a complete defect-less surface is important.

If you're worried, I would just spray zinc-rich paint there. The zinc-rich paint is recommended by ASTM standards for damaged corrosion protection on steel structures (e.g. scratched galvanizing or scratched paint). If any moisture is trapped under the paint or you missed a small spot, the zinc will act as the sacrificial anode delaying the rusting process. If it makes you feel any better, the frame would probably take anywhere from 15 to 30 years to rust through depending on how bad the salt is and how often you wash.
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      06-04-2009, 02:25 AM   #6
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Somewhat related, isn't the 3 or all BMW cars are protected by a 10-year warranty on rust?
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      06-04-2009, 02:49 AM   #7
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Yea, Im worried about scraches I made with some tools I used pulling out the broken tabs from the small holes under my door sills when I switched to M ones. I need to get some touch up paint.
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      06-04-2009, 05:16 AM   #8
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I'm not sure if this applies to every year, but it says in the Service and Warranty Information booklet that a biyearly inspection is required for the 12yr corrosion warranty. You could always have the dealer inspect the car if you're worried.

Last edited by jzchen; 06-04-2009 at 05:18 AM. Reason: Bad math.
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      06-04-2009, 07:38 AM   #9
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Wow, Andy knows his corrosion...
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      06-04-2009, 02:50 PM   #10
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Quote:
Originally Posted by Andy M View Post
Good catch, BMW does a cathodic dipped primer instaed of galvanizing. The paint doesn't have sacrificial anode properties like the zinc. However, even galvanizing will rust if the galvanized layer is scratched.

With cathodic dipped painting, it ensures that every piece exposed to air or water will be sealed with paint.

I had to check here to remember: http://www.bmw-plant-munich.com
(section Paint Shop in the Virtual Tour section)

But going back to the original question, if the exposed part where the plastic jack was got scratched or damaged, then it would rust since it's just paint. If it was galvanized, it would do better because of neighboring zinc will act as a sacrificial anode but all galvanizing will cease to work after a while. Even with galvanizing, it rusts after a while and a complete defect-less surface is important.

If you're worried, I would just spray zinc-rich paint there. The zinc-rich paint is recommended by ASTM standards for damaged corrosion protection on steel structures (e.g. scratched galvanizing or scratched paint). If any moisture is trapped under the paint or you missed a small spot, the zinc will act as the sacrificial anode delaying the rusting process. If it makes you feel any better, the frame would probably take anywhere from 15 to 30 years to rust through depending on how bad the salt is and how often you wash.
Very in-depth Andy
It doesn't look like there was any scratches, there are two big slots in the middle and one smaller slot on each side, they were already there though.
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