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Fuel leaks


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I recently purchased a RV9A. I have a slow leak at the forward wing root where the fuel lines enter the fuel tank on both wings. I replaced the fuel lines believing that was the issue. But that didn’t work. After about two weeks I still have seepage. I inspected the wings. No indication of fuel anywhere on the aft wing root nor the entire wing. I assume this is just a slow seep but I’m having a hard time finding it. Is there an easy way to easily handle this issue?
post some pics for us to see? try cleaning off all the blue staining to see where the seep is.
My right tank just about bankrupted me last month after it sprang a leak and piddled all that liquid gold over the hangar floor while I was away overseas. 50-odd litres at $3.01AUD a litre ($7.80USD/USG for those non-metric folk! :p )

It was traced to the rubber seal between the fuel quantity sender and the end rib. Vans no longer supplies this rubber seal, rather, they say to install the sender with tank sealant now. If you still have the rubber ones, that might be the issue - although I'd have expected the dye stain to be visible but your post suggests there's no visible evidence of such a leak?
Sounds like a perfect opportunity to drain the tank and check it using soap bubbles to show the leak.

The procedure on an installed tank would be to use blue painters tape or something like that over the fuel cap to prevent major leaks there, cap off the fuel line at the tank, and pressurize the system by placing an inflated balloon over the fitting on the tank where the fuel vent exits. Then spray the area in question with soapy water and look for bubbles.

Do not attempt to pressurize the tank using a compressor or something like that. Anything more than a miniscule amount of pressure can damage the tank.
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I just went through this on my my RV-10 right tank. Not sure if the 10 and the 9's fuel plumbing is the same, but for me it turned out to the the fuel pickup-finger strainer fitting. The sealant was at least 10 years old so it developed a seep. The worse part is draining the tank. After that simply unscrewed the fitting, cleaned up all the threads, reapplied new sealant, then reinstalled. I gave it a good 4 days to cure before putting fuel back into the tank.
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Someone asked for pics. Here they are last wing first then right. I thought it might be the service hole that the fuel line goes through. But maybe not. I may have to remove the tanks?


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Someone asked for pics. Here they are last wing first then right. I thought it might be the service hole that the fuel line goes through. But maybe not. I may have to remove the tanks?

Based on the pics, I'm willing to bet it's the same issue that I had. I'd clean everything, reseal, reinstall and then put some fuel back in and see if leaks again.

If you brought the airplane to me and asked me to attempt to fix the leaks I’d:

1. Pull both tanks for a detailed inspection. Is it leaking from the corner of the tank or somewhere on the back flange. My guess is the corner of the tank near the sump drain.

2. I’d pull the access panel (after draining the tank) and inspect that corner for sealant. I believe BruceH on the forum has a detailed write up about how he removed the existing proseal and resealed a tank.

3. If it’s the corner you might get by with resealing that area with Proseal.

4. Reseal the access cover, pressurize and test for leaks.

5. Hope you don’t need to create access panels in the aft bulkhead.
Thanks all. I think I have a plan. And hopefully I won’t have to cut an access. I think I’ll remove the tanks check for leaks with the soap bubble method and go from there.

The most likely suspect is the access panel in the inboard end of the wing
It is tight, but you can remove and reseal it without pulling the tank
I have done so twice in my 9A.
If there is either a cork or rubber gasket involved, that is the problem.
Overall, I agree with the suggestions above.
I have had to repair several leaks similar to what you have and having said that, it is mostly leaking around the access plate or at one or more of the screws.
It doesn't look like you have a gasket under the plate, so that's promising.
I will also say that sometimes the leak isn't where you expect it to be and the fuel is traveling.
If you touch the proseal with your finger and it is sticky, it is definitely leaking through the proseal somewhere.
Based on your pictures, there isn't an obvious spot to zero in on.
Check all the fuel line B-nut connections to make sure that isn't it.
The soap bubble test is worth doing but you won't be able to see the back baffles, which could be the source.
I would go for the simple solution first.
Clean it off as good as you can.
Spray some developer, from a dye penetrant test kit, on the area. It will leave a whitish powdery look. Let it set over night or go flying and any fuel seepage or leak will show right up.
If that doesn't work, I'd just take the tank off and test it with soapy water. VAN's sells a kit for this, but I usually just tie wrap a balloon to the vent outlet, close off everything else with a plug or tape and use some air pressure to blow air into the fuel outlet and blow up the balloon. (The balloon will keep you from over pressurizing the tank.) Use a piece of nylon tubing or something to blow the air in and then fold it over and clamp it to keep the air pressure in.
It's not that difficult, just a little time consuming.
Good luck
It is a pain to remove and replace a wing tank, but you'll have much better access to that inside bottom corner, after you remove the rib access panel, for inspection/cleaning/re-sealing.
You'll need every 1/4" universal adapter in your tool box plus another one between your wrist and elbow.
Fuel tanks removal

Anyone have advice for how to get to the bolts between tank and wing? My hands and arms seem to be too big. I can access the bolts but I’m having trouble getting my tools (I’ve tried many). To work. I’m using 3/8. Tried ratchet and ratcheting boxed end wrench.
I used an electric 3/8 inch drive ratchet made by Milwaukee. Just put the ratchet on the bolt head and a activate it.
You'll also need an open end wrench to break some loose. Once you've broken the torque, you should be able to spin them with fingertips or with a small socket held in your fingers.
I also used the Milwaukee ratchet - in fact I bought it specifically for this purpose.


To make access easier, I disconnected the fat aileron control tube on both ends and just slid it through rib openings to the outboard part of the wing so it wasn’t in the way. I think it took about 45 minutes to remove the wing tank all totaled. That ratchet made a big difference, and I’ve used it many times since for numerous other things. I’ve never regretted buying a tool after doing some research.
Anyone have advice for how to get to the bolts between tank and wing? My hands and arms seem to be too big. I can access the bolts but I’m having trouble getting my tools (I’ve tried many). To work. I’m using 3/8. Tried ratchet and ratcheting boxed end wrench.

Just had to do this a few days ago. My leak is at the outboard rib. I too disconnected the aileron pushrod. I loosened each bolt by hand with a deep-socket wrench, and then used an air ratchet to speed up the removal process. A few of the lower bolts were a pain due to not being able to see them, but overall the process took about an hour and I'm sure would be quicker next time.

I pulled these fuel tanks. I knew they leaked when I purchased the aircraft. I didn’t expect the leaks to be so prolific. However, this is a lot of patching on both tanks. I’m wondering if you would advise patching again or building new? I’ve never seen these outer tape like patches and as you can see the previous owner opened almost every section. I wanted to remove the outside patches and do it right. But I’m worried that these tanks will just continue to be a problem. (The patches match the wing color and are a bit hard to see).

Donald Kajans


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