I got my brand new NX450h+ in March of this year and I already noticed what looks like a rust spot on the paint. I have no clue what to do and figured you guys would know better than me. This spot is along the side of the car near the rear passenger wheel. When I run my finger over it, it feels smooth and doesn't feel like a rock chip or anything. Does it look like rust to you guys? I noticed it while trying to clean my car with a soft cloth and soap but couldn't get it to come off. Would this be something the dealer would cover since the car is practically brand new? And if not then how should I deal with it? I tend to like to DIY everything but if its better to get someone else to do it I'm open to that as wel.

 

If there is no indentation or hole, it is not rust from the underlying metal. but a rust stain from surface contamination. Lots of metal particles get on your paint from everyday use. Spray it with an iron remover (such as Sonax Iron, Carpro IronX, Chemical Guys Decon Pro) and follow directions. Usually, you spray it and let it dwell for 15 minutes, then wash the area with water. Your picture looks more like a surface contaminant rather than rust from the metal.

 

I took your advice and got some iron remover. It cleaned up the spot but it does seem like it is a spot of rust unfortunately. It seems like there's a pinhole in the paint and it rusted so fast. Not sure what to do about this and I'm assuming the dealer isn't going to do anything about it.

 

My first thought was iron contamination as well. If it is rusting, water is getting in. Either there was a rockchip (could be small) or a paint pinhole like you say.
I am not sure the dealership would help you much, it's too easy to blame it on a chip, and you'd have to wait until the problem gets far worse for them to admit it was a defect. And it will get worse unless something is done.

Either way the fix will be the same as if it were a rockchip.
I'd like to preface my advice with the disclaimer that I don't work at a Mercedes detail shop or anything, but I am detail oriented and have done this exact procedure on my own car. If anyone has better advice I'd like to learn it.

1. You need to get down to bare metal because of the rust. Rust is only possible because the metal has become exposed, and you will need to remove it completely before sealing it back up. You could use a very, very thin and fine point fiberglass pen ("Extra Thin Eurotool Fiberglass Pen on amazon). If the pinhole and affected rust area is even smaller, you might be able to try one of the pointed fiberglass pens. You rotate it to abrade the clear, color, and base all the way to bare metal in a small area. You should remove enough that there is no chance that rust still exists underneath the paint. That could be about 1-2mm diameter in your case. Then wipe the smallest spot with 70% IPA on the corner of a microfiber (try to avoid touching the surrounding paint)
2. Look up your exterior color paint code and order a paint touchup pen. It should be self-priming (or it won't adhere to the metal). Use the pen to get some paint out onto a sheet of aluminum foil. You might think this is dumb, but the paint pen is really imprecise and it is really easy to make mistakes with. Instead, take a toothpick and poke the tip into your paint puddle and stipple the exposed metal until you have it all covered. Let it try for several hours or overnight, then do it again - it will shrink while curing. Repeat until you build it up enough. If you are careful you can mostly blend it in. The only way to fully blend it in is to build it slightly higher than the surrounding coat, and polish it down - best not done if you have a ceramic coating or wax. Wax can be stripped, ceramic cannot easily.

You can use the same technique for other rock chips that will inevitably appear in the future.

 

It is what's called rail dust, basically, it some kind of particle from rail car or even possibly transport truck, Don't worry it is just the particle that is rusted not the car paint. Clay bar it and it will come off.


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