RUST on my 2009 C180!! W204

[Frontstep]

There are small dots of rust coming through all over the door unfortunately. Seems like it rusting inside out.

Inside out ! have many times had to explain the meaning of that on here,
luckily a Judge agreed with my Oxford English Dictionary definition.
Many an MB dealer and member here will try and tell you it means a hole to look through.

 

[Benzworx]

Good News - Mercedes have agreed to fix the rust spot for free and I get to keep the 30yr warrenty.

The little brown spots were actually tiny iron filings from the elctricity factory I live near. They will polish out.

They are not going to replace the door, just clean up the rusted area and respray. considering the rusted area is not on the main panel, the resprayed area shouldnt be too noticable.

I ahve a question. If the door is galvansied and it started rusting, doesnt that mean I wont have any zinc left anywhere on that door?

Quote: if the door was galvinised then it would not rust in the first place that is the whole point of it , so this now means that MB still have not got to grips with corrosion

 

[Lordcarter]

My understanding of zinc plated is that when the metal or zinc is exposed the zinc corrodes instead of the iron until all the zinc is used up. Galvanising only helps delay rust not prevent it.

If you look at oil rigs, they just have big lumps of zinc or a cheaper alternative strapped to the metal every so often.

So my original question, it's sounds like the zinc layer on that door is depleted.

 

[Boxbrownie]

My understanding of zinc plated is that when the metal or zinc is exposed the zinc corrodes instead of the iron until all the zinc is used up. Galvanising only helps delay rust not prevent it.

If you look at oil rigs, they just have big lumps of zinc or a cheaper alternative strapped to the metal every so often.

So my original question, it's sounds like the zinc layer on that door is depleted.

So we have sorted Mercedes' rust problem, all they need to do is bolt some sacrificial anodes to each body panel and we are all done, there's a ships chandlers down the road from me has them at a good rate

Joking aside your explanation is correct but I find it impossible to believe they have not got the process right! I would not be surprised if that rust stain is evidence of some migratory rust from the trim or even a result of some "nibbling" on the surface of the steel panel from a trim piece.
A large manufacturer from Essex had the same sort of problem on the rear cargo door of a popular model caused by a plastic trim, the cause was a small tail from the moulding process gradually rubbing through the paint and then the galvanic surface, thankfully it only manifested on a small percentage of vehicles due to the parts supplier not finishing the trim completely before chrome dipping it.

Anyhoo, good to hear they are going to sort it for you, although I would be surprised if they could anything but considering the age/mileage.

Lovely find on the car BTW, well done.

 

[Lordcarter]

I thought I should update this thread in case anyone else has a similar problem. So Mercedes took the car away in Feb/2013 and the door got fixed. By fixed I mean they sanded away the area and resprayed it. Grrrrr

Mercedes did admit it was a manufacturing defect that caused the problem.

So now 15 months later it is back. Not as bad as before (yet) but upon washing the car I found rust in the same area.

Hopefully the paint warranty still holds as they did the work and have admitted it was a manufacturing problem. Back to Cambridge I go.....

Cars only done 13k miles!