I've been noticing random black smudges forming on my rear doors close to the tire. Has anyone experienced this problem and know of any remedy?

 

wash your car, mang!!!
the black smudges looks like its coming from the door sill.
OPEN the door to see what it is....

 

these pics show that there is nothing on the car....
and any black smudges came from you/daily driving the vehicle.

 

someone did wash their car after driving in the rain, the TL tent to collect most of the gunk at that spot.

 

You are supposed to clean and grease those hinges in between the door and it looks like it might be picking up gunk in there. Its just a matter of washing it really. Try soap, if that doesnt work try a clay bar, if THAT doesnt work which I imagine soap will take it off, then you could use a compound. Looks like dirt to me though.

 

^yeah, it looks like it's coming from the door and wind speed is spreading it along the body

dude just needs to open the door to inspect what it is....
your thought of door grease may be correct.

 

If you have driven in rain especially on the interstate it is completely normal. I have had that happen to my car before but usually only on long trips in the rain.

 

Most noticeable on white. Happens to mine all the time. It's the air flow. Lot's on the trunk face too.

 

yeah I got a WDP and most of my travel is hwy due to work. Over here in rain city, I see those marks after about a week of driving, as a matter of fact I noticed them today and thought of your post on here. Car is need of wash is all!

 

Thank you for all the responses. Reason why I asked because my brother never had dirt build up in that area on his 07 TL type S but it's fairly easy to clean off. Just was curious to see if it was beginning stages to a big problem or something of the sort.

 

its just dirt.
OPEN the door and inspect where it's coming from.

the door grease idea sounds spot on!

so, you're driving at speed....70-80mph...water goes into the door crease and carries dirt and grime and grease over the body....

 

How fastidious is your bro about his car? Does he detail it all the time? I'm in the camp that think it's getting sucked out onto the door from the door sill or jam. You might be surprised to see how much crap can be on the under-sides of the doors and in jams and sills. I clean all of that every wash (cause I'm anal and hate seeing that crap when I open the door) So all that muck hiding on surfaces (and under the rubber seals) gets in the rain water and might just be getting pulled out where you see the dirt deposited on the outside. So I'd doo a full inspection of all of the inner door surfaces. Not what you see inside the car but all surfaces around the seals. The bottoms may be a mess.