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Black stuff around gas door

My 97 Corolla has had this problem for a while. Black stuff tends to build up around the gas door (you can see it in the picture). I can wash it off but it keeps coming back. I tried replacing the gas cap but it didn’t make any difference.

Also, I don’t know if this is related or not, but something similar is going on up on the driver’s side of the hood.

Any ideas?

That looks like mold to me… How does it react when you sprinkle a little chlorine and water on it? If it immediately starts losing color, drips off and disappears, it very likely is mold.

I sprayed a little mildew cleaner with bleach on it, and it definitely has an effect. The spot I sprayed dried completely clean. But how is it possible that mold is growing on my car, especially on the hood, when it sits out in the hot summer sun all day?

Is it safe to use mildew cleaner/bleach on the car, or can it damage the paint?

Edit: Just for fun I measured the temperature of the hood with an IR thermometer:132F

Any possibility the water drain behind the gas cap door is plugged?

I don’t know if thats mold or just plain dirt, dust, and pollen, from sitting out all the time. Dew forms on the paint in the morning, the wind blows the dust around and collects and maybe incubates the mold or just sticks to the surface. You really need to wash and wax the car if its sitting out all the time.

I’ve noticed that dirt collects inside my fuel door, and if I let it go long enough, water will get in there during rain storms and bleed some of that dirt out onto the side of the car adjacent to the fuel door.

My advice is to open the fuel door and clean as much gunk as you can from the area around the fuel cap. That should mitigate the problem until it gets dirty again. It probably wouldn’t hurt if guys like us washed and waxed our cars more often.

I’m wondering whether the ethanol or gas fumes somehow don’t attract mold. After all, it is organic in nature so it could be fed on by some organism.
I’ve seen that black stuff on other cars from time to time, all near the gas cap too, so that’s got to be a clue…

How old are the tires?

What you might be seeing is carbon black coming off worn tires.


Maybe, but why does it collect RIGHT above the top of the gas filler door? Click on the picture, it really stands out.

I wonder if there’s not some kind of leak in the fuel filler pipe or vapor recovery system in that area.

I almost always agree with Tester, but…this time…not so much.
I think that texases is onto something, and I wonder if the area on the hood where the black debris accumulates is very close to the carbon canister. If so, this could be a possible indicator of a vapor recovery system problem.

Hmmm…Here’s a question for the OP:
Is the Check Engine Light lit up?

No, no check engine light.

Any idea where the carbon canister is on a 97 Corolla? The only thing I recognize under that part of the hood is the master brake cylinder, but I know very little about cars. I’ll take another look later when I get a chance.

Those pictures just look like embedded dirt to me. I’d give the car a good wash and wax and see what happens. If you clean well behind the fuel door, I bet this stops happening until the wax wears off the the dirt builds up behind the fuel door again.

Wash, wax. Repeat when dirty. Problem solved.

You might want to stop by the Toyota dealer’s parts department and ask for an “exploded view” diagram of the evaporative emissions recovery system (vapor recovery). I no longer have access to technical data, or I’d be happy to look it up for you.

It’s hard to say without looking at the car, but I suspect the black residue coming from under the hood is simply oil seeping past the tired valve cover gaskets and burning on the exhaust, the rising fumes depositing carbon. In that engine I believe that intake is foreward of the engine and the exhaust manifold aft, so the fumes would be coming from that spot. I suspect they’re unrelated to the deposition above the gas door.

As regards the gas door blacking, are there any rot holes around the fill pipe and what shape is your exhaust system in? Is it possible that exhaust fumes could be coming up behind the gas door and leaking out past the upper edge of the door?

I am wondering if can be road moisture thrown up from the tires and leaking into that area.


Bob, are you aware that the OP posted the problem four years ago?

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