Wipe her butt?
 

Today having hit 60, I took the opportunity to wash my car. I couldn't help noticing that the dirtiest spot on the car was behind and below the fuel inlet. I'm careful when I refuel and I don't drop gas. Heck, I turn the nozzle upside down to be sure and get the last bit out. Yet there is a pattern of black gunk on the body there. Has anyone else encountered this?

I did try searching old threads but all the different incantations I tried kept coming back with bad fuel links.

If it's after you've washed your car, it is most likely water. I find there are a couple annoying spots you have to pay special attention to after washing the Z. The worst is the tail lights, water runs down and pools under the lights. So what you have to do is, take a deep breath, bend over, pucker and give the tail a blow. If you do it right, you'll see it run down the *** of the car. Best to do it somewhere where your neighbours won't see you. They might think you're weird or something.

No, it was all there before I washed it. I gave it a good run on the highway (ran to Costco and tanked up for the workweek) to dry it off.

I dry mine by starting with a California Waterblade, then blow dry the nooks,crannies,tail lights,door handles,headlights , mirrors, etc using my trusty leaf blower.No more water trails or drips on that first drive.

Could be water running down from the rear hatch area? Try opening the hatch and lifting it up all the way after a wash to clear pooled water. Could also be water pooling under the gas flap after a wash (painted metal gas flap). Water running out from that little area would be quite dirty.

Post some pics. We might be able to definitively tell you what the problem is.

Yeah, I washed it too soon. It is starting again though. I'll give it a week or two to get pronounced and I'll update this thread with pics.

My best guess is I've got vapor escaping from under the fuel lid and it is either condensing inside the inlet hutch or on the car and capturing dirt from the air (much as how ring around the collar works: you provide the sweat and oil and the air provides the dirt. Atlanta has a lot of particulates in the air)

i wash and use leaf blower, gets all the water out of those hard to see places.

Dry car, then you have the following issues:

Mirrors: I push them in, and use a towel to soak up the water, otherwise you'll have water running down the doors

Doors: Wipe down both the door jamb area and the underside of the door, paying attention to the rubber seal; I'm hoping this helps keep the seals preserved, plus who likes getting their work clothes dirty every time they get in/out of the car presuming you work in a dead end suicide inducing office job

Gas Lid: Open, wipe down

Rear hatch: This is the biggest problem area, pop it, wipe down the entire area especially the top as you'll have moss grow in there if you don't, and water will run down the passenger side, be sure to wipe both the jamb area and the lid itself.

Tail lights: A few seconds of holding a towel that can readily abosorb water will do part of it

Rear license plate area: water will drop out of here, wipe it down, bang on it a few times, and wipe it down again.

I've found driving the car for maybe 30 seconds back up the hill to my garage will result in more water, so I will have to wipe those areas down again, OR, wash n dry the car the night before, sit overnight, and it tends to have less repeat water seepage action.

Humidity/heat levels/towel type/direct vs. indirect sun make a HUGE difference. I've been using this maximus crazy $25 micro fiber from chemical guys washed in the microfiber soap.

Tip: Get your drying towel completely wet BEFORE attempting to dry the car, then wring it out as best as you can, and magically it seems to whick water back up much better then doing 3-5 passes and potentially scratching the car in the process, and then getting to hide out in the garage for five hours with the buffer (I do this 2-3x per year because I have no life and it's a Midnight blue and shows EVERYTHING: mistakes, nissan orange peel, lazyness, lack of claybar, lateral micro scratches); Man, when it's clean/shined up @ sunset, looks AMAZING plus it's a Z, so while car paint care is an unhealthy obsession, it's fun when you get a compliment or into a random conversation with another car lover, and attractive women who don't consume fast food constantly seem to appreciate a clean car :driving:

California Waterblade? NOOOOOOOOOOOOO!!!!!!!!!!

I got one from Santa Claus this year, so hopefully it will work as good as my wet vac with the hose in the exhaust position. I got one of the Worx Air blowers. https://www.worx.com/blowers-mulcher...wer-wg545.html

Well, it's winter here, so I'll have to wait a little bit before I give her a go. Supposed to be in the 50's this weekend, so I may get to use it on my Jeep Cherokee Trail Hawk :)

I own two of these:

https://www.chemicalguys.com/Woolly_...p/mic_1995.htm

So the "marks" image is from under the filler flap, I included a "cleanside" shot to emphasize that this is not water coming out of the light fixture.

I suspect that either vapor is condensing or maybe liquid is coming out and that makes the car sticky and the actual dirt is from the air. But I could be wrong. I am very careful when fueling and the streaks/spots become more numerous over time, so I don't think this is spill from refueling.

So I've gone further afield. I've found other people reporting the same problem with other models of car, but one in the same area as I am. And a posited theory that it has something to do with ethanol.

links:
https://www.answers.com/Q/What_can_i..._above_gas_cap

https://community.cartalk.com/t/blac...gas-door/81002

Black mold around fuel door - PeachParts Mercedes ShopForum

Still guessing, but I'm wondering if I don't have mold in the gas tank.

So I think I resolved this. The link I had found and related previously from the Mercedes forum seems to be the one. I had some black gunk under the filler flap that I thought was just oil or dirt from spill from the prior owner. After reviewing the Mercedes article and not getting traction from the community here, I hypothesized this was mold. So I used a bleach solution (Tilex) and an old sock and sprayed down the area under the filler flap and wiped out all the black gunk as best I could without taking things apart. It seems to have resolved the issue.