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Leaky fuel tank woes ... looking for perspectives


Immelman

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About a month ago I noticed fuel smell in the cabin and grounded my plane. The fuel was traced to be coming down the forward spar from the left tank. I have been a proponent of patches vs. complete reseal; in 10 years of owning my 66E I've had one leak and a simple patch job was sufficient. Looking at the logs, there have been just a couple of patch jobs, over 52 years! That's not bad. When I read that people spend $$$ for a complete strip and reseal and have leaks again after 10 years.... well, that gives me pause. "You can buy a lot of patch jobs for the cost of one reseal", and I have done most of the labor. I'm quite good now at removing, prepping, and resealing the access panels. Each attempt is ~$50 of sealant and 1-2 hrs of shop labor.

But my patience is wearing thin. We've now done three attempts at a patch and the leak is still there, showing up minutes to hours after fueling the tank. So far we've covered just about all of that forward spar top and bottom as well as the rib at the middle of the tank!!!

I will say that I have a great relationship with my local shop that handle a lot of Mooneys and is not new to patching tanks.... but after 3 attempts, I need a new perspective, a new method to consider.

1. My shop's method: look at the tank from the outside (borescope forward spar through the drain holes, etc), and estimate where new sealant is needed, cover over the original sealant.

2. Don Maxwell method: use vacuum with bubbles. My guys don't like this because they say that used to use it, but found that even modest vacuum could compromise the integrity of the old sealant causing more leaks.

3. Big $$$ method: strip and reseal.

My questions: does anyone have another method for locating leak? Any other considerations for making a patch successful? Has anyone had such trouble using vacuum (Don Maxwell method) on old sealant creating more leaks?

Finally.... if I do consider a strip and reseal - really a last resort - one thing sticks out in my mind: How can someone do this without creating a corrosion hazard inside the wing? By this I mean, if the stripping agents are corrosive... and you're removing all the sealant, surely come stripper will pass around the structure and remain in there. This seems like a big hazard to me.

 

Edited by Immelman
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Immelman,

Any interest in doing the strip yourself?

We have had a few done around here over the last couple of years...

Solvents are well known.

Sealants are well known.

Procedure is well known.

Experience Required.... done by first time owners... with other life skills.

Photographs Available... Probably by one of our youngest MS members.  :)

Limitations of old Sealants are pretty well known.

How long do you want to put this off?

Fuel in the cabin, takes a lot of fun out of flying. (Been there done that)

PP thoughts that may help your thought process. Not a mechanic.

Best regards,

-a-

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Bladders are an option also, but bigger $ than a proper strip and seal. What you are facing is most likely new leaks, not the old one you just patched. Expect this to continue until you bite the bullet and recognize the 52 year old sealant has met its end of life. 

So, your choices are

1) Patch new leaks continually and live with the constant leaks as long as the plane stays airworthy. Good luck if you try to sell it, you will be dinged here for sure on a prebuy and have to give up what a strip and seal will cost anyway

2) Put in bladders - Big bucks but your done with it for at least 20 most likely 30 years

3) Get it completely stripped and resealed by Weep No More and be done with it for at least 10 most likely 30 years.

 

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Thanks for the fast thoughts guys... more considerations:

I am inherently a DIY guy and am not necessarily opposed to a DIY reseal. I'd still want to be satisfied I won't corrode my spar! I found one writeup done by Doug Burright and have thought about it. However I have a baby at home, fly for an airline, and the time commitment is an issue. As it is I feel guilty taking a good chunk of my time off to chase this leak. I am curious how many labor hours are required for the DIY strip job. Again I've had the panels off so many times its no longer a big deal!

When it comes to dropping big $$ - someone mentioned resale... I am aware of the market for these airframes. Its not that great. I have to face the music here: with a high time engine, good, but dated (80s) panel, 80s paint, etc, my plane isn't worth much. I accept that. But it DOES give pause to dropping big money. The money I spend on this plane will need to be justified for my continued use of it. I could easily drop $10K into this thing and have an airplane worth.... $30K at best. Same with an IFR GPS, etc. I've had 10 good years with this airplane, I know it well.

Edited by Immelman
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17 minutes ago, mike_elliott said:

Bladders are an option also, but bigger $ than a proper strip and seal. What you are facing is most likely new leaks, not the old one you just patched. Expect this to continue until you bite the bullet and recognize the 52 year old sealant has met its end of life. 

So, your choices are

1) Patch new leaks continually and live with the constant leaks as long as the plane stays airworthy. Good luck if you try to sell it, you will be dinged here for sure on a prebuy and have to give up what a strip and seal will cost anyway

 

I disagree that a patch job may not last 5 years. Unless the sealant is breaking down a patch job last some time. Of all the Mooneys I know of on the field here none have had a strip and none are currently leaking. 

-Robert

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I used Maxwell's method but instead of soap I filled the tank with water and looked for bubbles. They are hard to see but you just need to be patient and have some idea where to look. I put a tiny party balloon over the fuel pickup to prevent any water from getting into that line.

i don't think the vacuum compromises the sealant but if it did maybe the weight of the water counter acts that possibility.

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1 minute ago, nels said:

I used Maxwell's method but instead of soap I filled the tank with water and looked for bubbles. They are hard to see but you just need to be patient and have some idea where to look. I put a tiny party balloon over the fuel pickup to prevent any water from getting into that line.

i don't think the vacuum compromises the sealant but if it did maybe the weight of the water counter acts that possibility.

I am slightly skeptical that the method used by the man who has arguably patched more Mooney tanks than anyone on earth could induce leaks.

-Robert

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7 minutes ago, RobertGary1 said:

I disagree that a patch job may not last 5 years. Unless the sealant is breaking down a patch job last some time. Of all the Mooneys I know of on the field here none have had a strip and none are currently leaking. 

-Robert

I do not believe I said it wouldn't last 5 years, Robert. What the OP, and you have been facing, is the original sealant springing new leaks. Thats why you are patching it every year (I believe you said that in an earlier post). Granted, you can patch a lot vs the cost of doing it right, but you have to live with the leaks as they spring up. If it makes you happy to continually be patching your tanks, I am happy for you. Would I buy your plane? probably not without it having a complete strip and reseal, or unless you had a 10K allowance for it in the price.

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I don't want this thread to devolve into the bladder haters versus the bladder lovers, but just as a data point, I'll go on record as a bladder lover.  20 years and counting.  Never a drip, a drop, or a blue stain.  I am not disparaging the strip and seal solution in any way.

Since it is just me and my wife 99% of the time, the slight loss of useful load is never a factor.  For a C model, there is a "slight" increase in fuel capacity.  It now appears that Griggs has taken over the bladder business, so availability of support is not a question.  However, I think everyone agrees that the bladder "once and done" solution is pricey.

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In patching your tanks, for those of us that have, do you use the two part patch first, wait a day and paint the single part, no catalyst sealer on top. Or..do you use one or the other only?

I haven't looked inside many tank but I could imagine some prior patch jobs may be very sloppy and therefor difficult to lay the patch on even and smooth. 

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41 minutes ago, nels said:

In patching your tanks, for those of us that have, do you use the two part patch first, wait a day and paint the single part, no catalyst sealer on top. Or..do you use one or the other only?

I haven't looked inside many tank but I could imagine some prior patch jobs may be very sloppy and therefor difficult to lay the patch on even and smooth. 

want to see sloppy? Here you go... drain holes sealed over, no required topcoat, sealant not on areas it should be, etc.. No wonder this DIY job now requires a pro to fix. Actually I understand it was done by an A&P even. If you dont know why these pics represent a lousy reseal/patch job, you probably shouldn't tackle it yourself. 

Names and N numbers withheld to protect the victim

Left Tank 1.jpg

Right Tank 1.jpg

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When my tanks were redone at Wet Wingologists in 2011, he told me that there were several patches of varying ages inside them both, but the underlying original sealant was breaking down, and had a sand-like consistency in some areas. Guess 41 years was all it had to give. 

At some point, you'll just have to redo them or install bladders. And at some point, the bladders will need to be replaced. There appears to be much variation in when that occurs, and only anecdotal evidence of what can be done to extend the timeline. 

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7 hours ago, nels said:

I used Maxwell's method but instead of soap I filled the tank with water and looked for bubbles. They are hard to see but you just need to be patient and have some idea where to look. I put a tiny party balloon over the fuel pickup to prevent any water from getting into that line.

i don't think the vacuum compromises the sealant but if it did maybe the weight of the water counter acts that possibility.

I used this method to help a client of mine find and repair his fuel tank.  It work well at finding the leaks. Easier to spot the single bubbles rather than looking through a foamy pile of soap bubbles.

Clarence

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When I got my C the right tank was seeping and later started dripping.  I used Don Maxwell's method to find the source of the leaks but instead of patching over the bad areas I stripped just the bad area, probably about 18" in the bottom inside corner, and resealed it.  That was over a year ago and it is still leak free.  I don't think the vacuum could cause additional leaks.  After stripping I rinsed it several times using water and dried it with a blow dryer then cleaned it with MEK.  I would patch mine at least once again before getting it stripped and resealed. I would not however attempt a total reseal as that would be too much fun for me.  

I recommend trying it again using Don's method as it is almost impossible to find the source of the leaks otherwise.  Good luck

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5 hours ago, mike_elliott said:

want to see sloppy? Here you go... drain holes sealed over, no required topcoat, sealant not on areas it should be, etc.. No wonder this DIY job now requires a pro to fix. Actually I understand it was done by an A&P even. If you dont know why these pics represent a lousy reseal/patch job, you probably shouldn't tackle it yourself. 

Names and N numbers withheld to protect the victim

Left Tank 1.jpg

Right Tank 1.jpg

I agree. It appears the repair person was more interested in quantity than quality. The spots he missed are very obvious and just a hurry job. The secondary single stage coat could have sealed what he missed and I believe the intent of the secondary coat is meant to fill the pin holes or blisters left from the application of the heavy primary coat. The second application is really important for a fool proof job. Hence the reason for my question:  do the guys here who have done this job follow up with the thin sealant or do some just use the thin sealant for a patch.

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I patched mine several times.  I have done roofing and this reminds of putting henry's around roof jacks.   After several repairs on a 47 year old plane, I had Advanced Aircraft in Troutdale do a complete strip and seal.  Money was well spent.   As a DIY guy myself, I would not do a strip and seal myself.   Some things are better left to the professionals.

Ron

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2 minutes ago, Brandontwalker said:

Got a question. When replacing the access panels, how do you hold it in place while starting the screws? Suction cup?


Sent from my iPhone using Tapatalk

I make a loop with painters tape. One end touching the panel the other end wrapped around my hand. It’s not super sticky but you just need 2 screws started.

-Robert 

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FWIW, when Maxwell's shop patched my tank they said sometimes it's hard to pinpoint the source of the leak even with the bubble method, since the bubbles can travel underneath the sealant before they appear in the tank.   So where the bubbles appear in the tank is not necessarily where the fuel is getting out of the tank.

Basically, wet wings are kind of a pain when they age.

 

Edited by EricJ
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22 minutes ago, Brandontwalker said:

Got a question. When replacing the access panels, how do you hold it in place while starting the screws? Suction cup?

Suction cup wont work on the wing walk area, I prepped the panel and placed in the tank then used 2 rods that I threaded and pulled into place with them. 

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7 hours ago, mike_elliott said:

want to see sloppy? Here you go... drain holes sealed over, no required topcoat, sealant not on areas it should be, etc.. No wonder this DIY job now requires a pro to fix. Actually I understand it was done by an A&P even. If you dont know why these pics represent a lousy reseal/patch job, you probably shouldn't tackle it yourself. 

Names and N numbers withheld to protect the victim

Left Tank 1.jpg

Right Tank 1.jpg

Clarence, I thought for sure you woul spot the obvious issue here Hint: Sealant doesn’t adhere well to primer

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