Quote:
Originally Posted by raj55
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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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.