DA40: Fuel stains around drain

[BRS]

I topped the tanks the other day then later noticed the fuel stains in the picture. Who has seen this before and what causes it?

[Kai]

Brock,

I have had it. It was a leaking fuel line. We had two theories why it happened:

1) Age
2) Porosity after using MoGas. It turned out that the fuel lines are not certified for use with MoGas.

This was also the time when I realized that fuel lines need to be exchanged periodically and none of the repair shops has ever done it during the annual inspections.

Nevertheless, you might as well have only a leaking washer or o-ring.

Btw, the fuel stains are really hard to clean so it would be in the best interest to address this issue as soon as possible. Meanwhile, you might want to put some cloth into the gap so the fuel drips on the floor and does not run along the plane.

[Chromer]

I had the same problem once, I had taken the fuel sample before a flight and there must have been something that held the sump drain open just enough to allow fuel to drip out. I didn't notice it until the next day. I used the sample tube to take more fuel out, cleaned around the drain and watched to see if it would leak, it did so I took another sample and pulled down on the drain ever so slightly, it worked and the problem has never returned.

[Steve]

Pull the fuel drain access plate off and look around with a flashlight and inspection mirror. That is your best chance to determine the source of the leak.

[Rich]

There are several other fittings at the inboard end of the tank. For example mine developed a leak at the low-fuel sensor mount. There are also, of course, the fuel line, and electrical "potting" points for the fuel level probe, the probe itself, and the potted entrance for the low-fuel warning.

So be sure to examine the inboard end piece where these things go in.

Of course, it's also possible for the tank itself to develop a leak.

[BRS]

Turned out to be the fuel sender threads on the outboard tank. Fixed (I hope) now.

[DavidS]

Oof. Hopefully you didn't have to replace the fuel sender in the process. They're... annoyingly expensive. (Side note, I love seeing how robust our fuel tanks are.)

[Lance Murray]

I think this a typical problem caused by cross threading the threads for the fuel sender during installation. Be very careful when installing the fuel probe.

[BRS]

Didn't need to replace the fuel sender and the threads were fine. Don't know why it leaked but the tech reinstalled with some sealer (permatex?) and it hasn't leaked. For awhile I'm trying to use the other tank for takeoffs in case they used just a bit too much sealant.

[Rich]

This problem just materialized yesterday on my plane. Didn't have the wherewithal to check into it further at the time. Will bring the necessary stuff to the airport tomorrow and check into it. One hopes a minor bit of thread goopy will fix the problem. It's been years since the tanks were fooled with, when I had to replace a fuel level probe.