Dealing with Fuel Tank Leaks

I hope this post may be of use to those out there struggling like I am with a leaky fuel tank. I have a few pics and videos to show concerning my process along with a question concerning something I found in my fuel tank that I would like to understand.

I have been fighting fumes in the cockpit pretty much since my first flight. I have approximately 150 hours on my 9A now. I have always had a distinct smell of fuel whenever I would initially open the canopy prior to flight. The fumes have always dissipated on the ground once the engine was started. I attributed this to the air movement through the cockpit once the prop was spinning. I have never smelled fuel at any time during flight, only on the ground prior to engine start. Up until just a couple of months ago I had never seen any visual indications of a fuel leak, only a smell of fuel when I initially opened the canopy. However, back in November after fueling up one day I knelt down to take a look underneath the wing to see if there was any indication of fuel anywhere. There it was. There was a line of blue dye along the trailing edge of the fuel tank running from the fuselage outboard to the first inspection plate.

Well that was it. I grounded the plane in December. Over the Christmas/New Year holidays I pulled the left fuel tank off to see if I could fix the leak. I will not go through the process involved in pulling the fuel tank except to say that even though it does take a couple of hours of physical contortion to get back into the back side of the wing spar to remove 21 bolts and, every time I do this, the process does take some skin off of my hand, wrist and forearm, overall the process is doable.

At any rate, to shorten this post, I removed the tank in December and did the typical soapy water bubble test only to find . . . NOTHING! I pressurized the tank for days with a balloon that pretty much held its pressure. I was never able to see any bubbles form with the soapy water. I did see where there were some blue dye stains so I took some ProSeal to that section of the tank along the rear baffle seam and along one of the Z-brackets. I let it cure for a week and pressurized it again. It appeared there were no leaks. So, I put the tank back on.

I am sure you know what happened next. After 3 or 4 flights I looked again underneath the wing. Yep! There was the blue dye again. Only this time it was worse! So, this weekend, off came the tank again. Again, I put the balloon on the tank, sealed it up and pressurized it. Only this time around the soapy water revealed multiple pin hole leaks along the bottom rear baffle seam. I took some pictures along with a couple of videos of my process.

Click on the picture below to see the first video of the leaks along the bottom rear baffle seam:



After some deliberations I decided I could take the end plate off of the tank and with a long screwdriver reach through one of the rib baffle holes and get to the inside of the seam with some ProSeal. In the video above you also saw a leak in the far outboard corner of the rear baffle. I was able to reach down through the fuel filler opening to get to the inside of that seam.

Click on this picture to see the other video showing the inside of the tank after the access plate was removed.



So, if you watched the video you noticed the question I had. I noticed some fine powdery type residue on the inside of the fuel tank. The pictures do not really show all of the inside of the tank but it did look like the residue was mostly on the floor of the tank. From what I could tell, especially when I look closely at this picture it looks like this residue is from the ProSeal:


You can clearly see where the ProSeal on the reinforcing stringer on the floor of the tank is flowing outward from that seam.
[ed. 2/23/12, just in case you may not read all the way to the end of this thread I have discovered this residue is rust from my steal fuel storage tank I use for my 100LL fuel source. RVbySDI]

So the questions I have for everyone: Has anyone seen this before? Should I be concerned with it affecting the fuel as it flows into the engine? I would guess the filter(s) will catch most of it. Any thoughts at all would be appreciated.

I have the fuel tank sitting in my living room floor now in front of the fireplace. It will take several days for the ProSeal to cure. After that I will seal the access plate up and pressurize the tank again. We will see if my patch worked or if I missed. I was having to go more by feel than sight especially when I had to reach through the small baffle hole in the first rib. It is completely possible I could have missed sealing that section of the rear baffle seam. Once it cures and I can test it again I will have a better feel for whether I will have to reach into any of these areas from the inside again or not. Time will tell.

Click on https://picasaweb.google.com/114083177287781041474/FuelTankRepairs?authkey=Gv1sRgCILc6YSAxIOlMA to see all of the videos and pics I took while working on this repair.

Residue

Steve

Did you build the tanks?

What type of fuel are using? Any auto fuel?

I've never seen residue like that when using 100LL.
Better find out what it is before flying again.

Carr

Carr said:

Steve

Did you build the tanks?

What type of fuel are using? Any auto fuel?

I've never seen residue like that when using 100LL.
Better find out what it is before flying again.

Carr

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Yes, I built the tanks. I have never used anything except 100LL.

That sealant looks like it has a brown tint to it, is that true or is it just the camera? The sealant migrating out from the stringer looks like it is actually dissolving, that's not a good sign and what you are seeing is NOT normal.

PS: Normal B-2 sealant should tack free in about 2 hrs, at 70d it should be firm in 24 hours max, it does not take several days.

What type/brand of sealant was it and how old is it?

Walt said:

That sealant looks like it has a brown tint to it, is that true or is it just the camera? The sealant migrating out from the stringer looks like it is actually dissolving, that's not a good sign and what you are seeing is NOT normal.

PS: Normal B-2 sealant should tack free in about 2 hrs, at 70d it should be firm in 24 hours max, it does not take several days.

What type/brand of sealant was it and how old is it?

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A couple of months ago I purchased a quart of B-2 Flamemaster from Van's. There was a slip with the tank sealant that says that it will take 3 - 7 days to cure, and will remain soft for up to 30 days.

Even after a week of curing and extra heat, it was still somewhat soft. Not tacky, but certainly not solid. I used a 1g resolution scale so the ratio was exact. My sealant also has a brown tint to it. Maybe that is a characteristc of Flamemaster over Proseal??

Walt said:

That sealant looks like it has a brown tint to it, is that true or is it just the camera? The sealant migrating out from the stringer looks like it is actually dissolving, that's not a good sign and what you are seeing is NOT normal.

PS: Normal B-2 sealant should tack free in about 2 hrs, at 70d it should be firm in 24 hours max, it does not take several days.

What type/brand of sealant was it and how old is it?

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The sealant does have a brownish tint to it. I used Flamemaster B2 from Vans. I built these tanks in 2008-2009. Those tanks cured for about 4 weeks or longer before I ever sealed up the rear baffle. They spent another 2+ years sealed and empty before I ever put fuel in them while I built the rest of the airplane.

I know there are bound to be a lot of opinions about this and I welcome all comments. Never the less, I would greatly appreciate anyone who may have any first hand experience with this. Better yet, is there anyone out there that can do a chemical analysis of this material to find out for sure what it is? If it is the Flamemaster B2 sealant I would like to know what is causing it to break down into this powder like substance.

I just thought of something while looking at the video again. I think this potentially could be rust. In fact my thoughts are that it if it is indeed rust then I know the source. I have a 300 gallon steel fuel tank that I use to fuel my plane. It has a filter on it that is designed to keep this type of contamination out of the fuel but my guess is that rust from the steel tank is making it through the filter and into the fuel tank. It definitely has a reddish-brown tint to it that reminds me very much of rust.

I think I am going to pull the filter off of my fuel tank and see if it has the same substance in it. I will post when I can get out to check it.

I've never used the Flamemaster, I've always used PRC Desoto "ProSeal" and have used the AC Tech for repairs with no issues (it is also dark gray). For building tanks I personally would only use PRC (this is what I've used/seen used my whole career) with good results (very rare to get a bad batch). We would seal a tank and put fuel on it 8 hours later with no problem. Using B-1/2 we would put fuel on it after just a few hours if we were in a rush.

Same for me Walt...PRC Proseal from ACS.

The military uses it for a reason. I thought I would try a little Flamemaster from Van's. It cured slower and it had a different smell. I used it on everything but my tanks. Scothbrite all mating surfaces and 1/2" beyond. Clean with MEK. Spend the extra money on PRC proseal and don't be stingy...it only adds a lb or two more. Go over all accessible proseal with PR-1005-L from ACS(red Buna-N). It bonds great to proseal and bare, scuffed aluminum. Pressure test to 1 psi using homemade or electronic manometer. By all means build your own tanks.

Note in one pic above...I notice many are not putting proseal on both sides of ribs and also not covering all rivet shop heads. The proseal adds a bunch of strength to those joints to prevent loose rivets/weeping rivets down the road.

Red sealant

Is there a brand name for the red sealant mentiioned here..haven't found it at ACS( assuming that means Aircraft Spruce..right? )
Thanks
Tharpo

red sealant

You would think that someone whose nickname used to be "Red" could have "read" a little more closely.....I just saw red after a second look. Disregard my last.
Tharpo

Walt said:

I've never used the Flamemaster, I've always used PRC Desoto "ProSeal" and have used the AC Tech for repairs with no issues (it is also dark gray). For building tanks I personally would only use PRC (this is what I've used/seen used my whole career) with good results (very rare to get a bad batch). We would seal a tank and put fuel on it 8 hours later with no problem. Using B-1/2 we would put fuel on it after just a few hours if we were in a rush.

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The jury is out on tank sealant IMHO.

My QB tanks built in 2002 were done with Proseal, no question of it. But they leaked a gas around rivet shanks causing paint blisters forever. I finally built new tanks last summer using Flamemaster from Vans. So far they are OK. No blisters as of this date that I know of.

I kept some of the paper plates used to mix the stuff for a while to see how it would set up and cure. In every case it cured quite firm in a few days.

A couple weeks ago I decided to use some of the remaining Flamemaster (out of date) in the rudder and elevator skin bend area as called for in the build plan. I did not weigh the mixture this time but just mixed it until the color looked about right, it too cured very firmly in a couple days.

Technically, I believe Proseal and Flamemaster meet the same military specs. The only difference is the price and that's why Vans uses Flamemaster.

I don't have a clue what is going on with the tanks precipitating this thread. There was a report a while back where the sealant on the exterior of the tank became soft when fuel leaked through to it suggesting there was something going on when oxygen is present with fuel and the sealant. I never heard an explanation as what did cause the sealant to go soft beyond that speculation.

The brown stuff in the tank is suspicious. My first thought was residual matter from fuel that had evaporated. But it could be sealant breaking down. If so, there is something really wrong with that batch. These sealants are designed to withstand fuel.

David-aviator said:

. . .There was a report a while back where the sealant on the exterior of the tank became soft when fuel leaked through to it suggesting there was something going on when oxygen is present with fuel and the sealant. I never heard an explanation as what did cause the sealant to go soft beyond that speculation.

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The bead of sealant along the outside seam of the rear baffle in my first video has this happening to it. In December when I first pulled the tank off I contacted the Van's builder assist and talked to them about this issue. Although I cannot remember which individual I talked with at that time, he did state this is common for the sealant to do this when leaking fuel and air mix and come into contact with the sealant. He also stated once the leak was stopped and there was no longer fuel contacting that sealant it should solidify again with no harmful effects. I did see this occur in a section of that bead that did not have fuel leaking on it any longer. Conversely I also saw where the sealant that did have fuel still leaking on it was still tacky.

David-aviator said:

The brown stuff in the tank is suspicious. My first thought was residual matter from fuel that had evaporated. But it could be sealant breaking down. If so, there is something really wrong with that batch. These sealants are designed to withstand fuel.

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I have not been able to get back out to the airport to check on this yet, but I am still leaning toward the idea that the brown stuff could be rust from my steal fuel storage tank. This makes sense to me more so than the idea that the sealant is somehow dissolving. Once I am able to check it out I will be sure to post on here my findings.

Magnet will tell you if it is rust.

Wayne Gillispie said:

. . .Note in one pic above...I notice many are not putting proseal on both sides of ribs and also not covering all rivet shop heads. The proseal adds a bunch of strength to those joints to prevent loose rivets/weeping rivets down the road.

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Wayne,
Just to be clear, the photos and video I took of the rear baffle area were AFTER I had cleaned off any residual sealant around the bottom flange of the rear baffle seam where I found the leaks. Prior to the repair process I did indeed have a solid bead of sealant across the entire baffle seam and made sure all rivets were covered with sealant.

Thanks for your comments and observations. It really does help to have other's eyes looking at things. Without the ability to post pictures and videos on this forum I do not know how I would be able to have such experienced eyes examining my problem(s).

Mike S said:

Magnet will tell you if it is rust.

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Well there you go! Just as I finished typing my previous post on how great it is to have a forum like this where I can tap into the wisdom of others, along comes your post. I don't know why I didn't think about that. Duh! I will see what a magnet will reveal.

I vote for rust

If its in the tank settling out you should find in bottom of carb bowl, thats where I have seen that same kind of red powder when dry.

67MK Larry said:

If its in the tank settling out you should find in bottom of carb bowl, thats where I have seen that same kind of red powder when dry.

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Agree with you on that, except this will not apply in my case. I have fuel injection. If it is getting picked up and makes it through the filter(s) I will have to concern myself with these particles possibly clogging fuel injectors.

Yep

That is certainly and issue, by the way how about a used aluminum tank off a wrecked big truck, I am in trucking business a had rusting steel tanks replaced with aluminum tanks off a wreck. They come in 50 , 80, and 100, and 150,s usually for your storage issue.

Truck storage tanks

Steve just looked at Ebay there are two 100 gallon tanks for 175.00, their in Pa

67MK Larry said:

Steve just looked at Ebay there are two 100 gallon tanks for 175.00, their in Pa

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I like the idea of aluminum. My current steal tank is 300 gallons. I would like to have at least 200 gallons to make it worthwhile. I have my current tank mounted on a trailer and I haul it to whichever airport I can get the best price on.

I will have to check into this. By the way, not sure if you were thinking the tank you mentioned is near me or not, but I actually live in Oklahoma. I guess I need to find one close to me here.

Slimey residue

Steve does the residue have a slimy feel to it? If so it may be bacterial growth. It?s uncommon in gasoline however more common in Jet fuel.

Sometime free to ship

In the trucking world there is a lot of back hauling, and mt space, if its a private trucker or even a wholesaler ask if they could get to a terminal near you I moved a guys car from East coast to ICT for 100.00. You have to ask. A semi truck bone yard is always near major cities. Here in Chicago area there are places for semi parts all over. Get on Craigss list. 10-4?

kevinsrv7.com said:

Steve does the residue have a slimy feel to it? If so it may be bacterial growth. It?s uncommon in gasoline however more common in Jet fuel.

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No, it is a dry dusty type consistency. My wife and I did some testing with some of the residue last night as Mike suggested. It was magnetic indicating it to be rust. Rust from the steal storage tank is the most logical explanation. I am going to start with changing out my filter on the storage tank. It is designed to filter out rust but it has been on for a while so it is time to change it. Then I will start thinking about finding another storage tank. I like the idea of an aluminum tank as Larry suggested. Now if I can find one that will work for my situation.

67MK Larry said:

In the trucking world there is a lot of back hauling, and mt space, if its a private trucker or even a wholesaler ask if they could get to a terminal near you I moved a guys car from East coast to ICT for 100.00. You have to ask. A semi truck bone yard is always near major cities. Here in Chicago area there are places for semi parts all over. Get on Craigss list. 10-4?

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Thanks Larry, I will look online. If you have any leads or if you think you could help with delivery I would love to talk with you. Drop me a PM anytime.

Let me start looking

The 2 150's option would get your 300 gallons, let me get sizes, being so close to Ok City should be a plus. Im kinda busy right now I will send a pm in a couple of weeks. Good luck with resealing, my wife and I will be in Ok city in June, we are flying RV-6a to West Coast and stop to see wifes relative.

67MK Larry said:

The 2 150's option would get your 300 gallons, let me get sizes, being so close to Ok City should be a plus. Im kinda busy right now I will send a pm in a couple of weeks. Good luck with resealing, my wife and I will be in Ok city in June, we are flying RV-6a to West Coast and stop to see wifes relative.

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Drop me a note when you can. Would love to have you visit when you come to OKC in June. We have a hangar and place to stay, if you need either or both.

leaking tanks make me sick...

Steve, thanks for sharing your experiences... seeing your photos just makes me sick. Hang in there. I hope that you can get it resolved soon. For what it's worth I used the same Flame master product from Vans. I never had a batch that looked brown though... always a dark grey to black.

[email protected] said:

Steve, thanks for sharing your experiences... seeing your photos just makes me sick. Hang in there. I hope that you can get it resolved soon. For what it's worth I used the same Flame master product from Vans. I never had a batch that looked brown though... always a dark grey to black.

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Mine is a dark grey also. I have made an edit to my original post as I am now thoroughly convinced the brownish residue is indeed rust from my steal fuel storage tank.

My original comment concerning the last picture was based upon my perception that it looked like the tank sealant on the bottom stringer was flowing out away from the seam. It did indeed appear that way. However, when I go back into the tank and look in person I can see the sealant in that area is solid. What looked like flowing sealant was a trailing piece of sealant that was formed when I initially applied the sealant. If you built your tank using ProSeal or Flowmaster you know what I am talking about. When whatever tool you use to apply the sealant is pulled away from the area a small string of the sealant is pulled away also until it finally lets go of the tool. It truly is like pulling taffy.

I again did some more exploration of the fuel coming out of my storage tank last night. I took apart the filter and filter bowl off of the storage tank. When I took a magnet to the inside of the bowl there was a small amount of rust stuck to the magnet. So, I am going to be replacing the filter and keeping a close eye on the fuel. I am on the search for a replacement storage tank now. If there is anyone out there with a lead on a non-steal fuel tank that will hold around 300 gallons please contact me. Has anyone ever welded up their own aluminum fuel tank? I am wondering how difficult it would be to construct my own. Any thoughts?

Going back to the leaks that started me down this road, I will be putting the access plate back on Saturday and will pressurize the tank back up to see if my sealant patches have stopped the leaks. Stay tuned for information on that.