Fuel seep out drain hole in M20J

[Groundhog]

Hi all! I’m a brand new owner of a 1978 J, and after my prebuy/annual at a MSC I noticed a fresh fuel stain around what appears to be a drain hole near the wing root of the left wing skin, well forward of the drain sump. First of all, I was just wanting to see if anyone can confirm that this is actually meant to be a drain hole in the skin. Also, is there anything I should do to troubleshoot before talking to the shop about it? I’m guessing they didn’t see a leak because that tank was relatively low level during the inspection. I filled up before I flew it to my home airport. Thanks in advance for any advice!

[N201MKTurbo]

See if it only leaks when the tank is full. It will help isolate where the leak is.

These are hard to isolate, you can’t see much in the wing ahead of the tank. You can use a borescope, but even then it is hard to tell. Either way, you will have to open the tank to repair it.

[Groundhog]

Would you suggest flying it on that tank to burn off a certain amount of fuel, and checking afterwards to see if it leaks? Then burn off a little more at a time to try to determine the level it leaks at? Or is this a no fly issue? 

[N201MKTurbo]

8 minutes ago, Groundhog said:

Would you suggest flying it on that tank to burn off a certain amount of fuel, and checking afterwards to see if it leaks? Then burn off a little more at a time to try to determine the level it leaks at? Or is this a no fly issue? 

Sounds like a plan. If you find the level it doesn’t leak, you know the leak is above that. It is usually the top seam, often the top front inboard corner.

[EricJ]

37 minutes ago, Groundhog said:

Would you suggest flying it on that tank to burn off a certain amount of fuel, and checking afterwards to see if it leaks? Then burn off a little more at a time to try to determine the level it leaks at? Or is this a no fly issue? 

The guidance in the maintenance manual is that it isn't a flight issue until it leaves a big enough stain on the ground (seriously).   So if it isn't making it to the ground, it's an annoyance that needs to be monitored.    Many Mooneys have leaks like this.    I know just how much to fill my left tank before it'll start leaking.   

The tank can be patched and some MSCs (or shops or A&Ps) will do this.   Maxwell's shop patched one of my tanks for a flat fee several years ago and that patch is still fine.

 

[Groundhog]

Thanks guys! I’m new to all this and still learning. I knew when I bought it that a tank patch or reseal could be in my future, but was hopeful when the MSC didn’t find any evidence of leaks. I wish I would have fueled it up before I did the inspection!

[Ragsf15e]

Find out what level it leaks at.  If it’s an acceptable fuel level for your mission, just stick with it.  If it’s not, seek an experienced place for a patch.  It’s not terribly hard, but it’s kind of an art finding and fixing inside a fuel tank.

[Skates97]

My plane had a full strip/reseal done a few years prior to purchasing it so I thought I was home free. After purchase I found that if I filled the right tank I had a leak that showed up right where it looks like yours is at. I could remove the small panel in front of it and see it coming down the front corner of the tank. I called up Wetwingologists and he said he would be happy to fix it under warranty but that would have been a flight from CA to FL. He said during the curing that sometimes there will be a small bubble in the sealant that can pop and leave a small leak. I filled the tank one night and stuck a rag in that hole to soak the fuel and keep it from running down the underside of the wing. In the morning I took the cap off and found it down to about 20-22 gallons left. No AP wanted to mess with it so I flew it that way for a few years, I just didn't fill the right side.

I moved to a new field and had an AP/IA that was okay with me opening it up and working on it, he would supervise, but he didn't want the responsibility of another leak and me coming back to him because "he was the one who fixed it." I think that's also why none of the others wanted to touch it. Where it leaks is not always where the leak is coming from, but working from a fairly new complete reseal I opened up the tank from the bottom. I also suspected it was in the front part of the tank and knowing the level it leaked down to I knew about how high to look. We found a tiny hole in the sealant, fixed it, and it has been trouble free ever since.

There is also an excellent article by Don Maxwell on how they find and fix leaks.

Fuel Tank Repair.pdf

[A64Pilot]

18 minutes ago, Skates97 said:

Where it leaks is not always where the leak is coming from

 

 

Fuel Tank Repair.pdf 408 kB · 1 download

Truer words were never spoken, the actual leak can be several feet from where it appears, it can and will run under the sealant to pop out somewhere else.

There are products made ro lay over the B2 to seal it. one we called Monkey Blood because it was red.

‘I’d advise avoiding these products, sometimes they work, but often they don’t work for long 

[Guest]

From the maintenance manual, fuel leaks in areas not exposed to slip stream (inside the wing) must be repaired before flight.

Clarence

[Guest]

10 hours ago, Groundhog said:

Hi all! I’m a brand new owner of a 1978 J, and after my prebuy/annual at a MSC I noticed a fresh fuel stain around what appears to be a drain hole near the wing root of the left wing skin, well forward of the drain sump. First of all, I was just wanting to see if anyone can confirm that this is actually meant to be a drain hole in the skin. Also, is there anything I should do to troubleshoot before talking to the shop about it? I’m guessing they didn’t see a leak because that tank was relatively low level during the inspection. I filled up before I flew it to my home airport. Thanks in advance for any advice!

There should be an inspection cover near this drain hole, open it for further investigation.

Clarence