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Patching The Wet Wing Tanks


mooniac58

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During the paint job they discovered I have a very slight fuel leak in one of my tanks.  While it does not even drip fuel at this point it would not allow the metal to dry and caused a small 2x2 area that paint did not adhere to well.  The paint shop says that if my A&P can Proseal that from the inside of the tank he will redo the paint there at no charge.


My question is: Can you do this?  Can you just do a "touch up" job on the inside of the tanks to stop leaks or is a complete re-seal needed at this point?


I would like to be able to patch it for now since I doubt anyone here in Hawaii is qualified to do the job and I expect to have N5801N back on the mainland in under 2 years, where it can have a proper re-seal done at Lone Star Aero.


Thoughts?

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Yup you sure can just do a reseal...the hard part is finding the pin hole it is leaking through.  I just did this a month ago on my Mooney.  My IA takes off the top covers and puts plexi glass over them sealed air tight.  We will the tank with water, about half way.  Then stick a vacuum on the tank vent and suck out the air, I usually don't hold it flush but you may have to.  Have a light in the tank and watch for little bubbles.  I wouldn't be surprised if you find more than one hole, and it probably won't be where you expect it.  When done make sure to get all the water out and when you go to fly, I wouldn't use that tank on takeoff! Smile


There is a website somewhere that details this process....I'll see if I can find it.

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The best method to find a leak is by air pressure test. This is the same one used by the factory and all wet wing aircraft manufacturers including Boeing. For a Mooney the procedure is as follows:


1. Empty the tank completely and let it dry for at least 24 hrs.


2. Set the fuel selector to the opposite tank and install the fuel cap.


3. Connect a 3/8" hose to the tank vent and clamp it. For M20Js and before usea smaller hose and seal the coaxial vent tube.


4. Blow air by mouth only into the tank as much as possible. This will insure no excessive pressure will go into the tank.


5. Bend the hose or keep pressure into it (if it is a big leak).


6. On the suspected leak and adjacents areas spray SD-20 foamy cleaner and watch for bubbles. You may need to remove dry areas inspection panels to get to the leak outlet. You can also use a hose as an stethoscope to listen for leaks.


Boeing and other big manufacturers use ultrasonic generators in a pressurized tank and then listen for the sound wave coming out of the leak with an ultrasonic sensor. Same procedure is used for the pressurized cabin. For a 5,000 gallon tank no one is going to put fuel or water when air is simpler, quicker and cheaper.  


 

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Craig,


I have uesd the "Don Maxwell" method to sucessfully patch a small leak and find it very effective at accuratly identifying the leak.  I used vacuum controled with an fish quarium style air regulator and an old altimiter to create a slight negative pressure.  The soap suds bubbled away just as Don says it will.  Also, I am not a believer in a complete reseal just to fix a leak.  In my world of C-5's with huge tanks, 49 thousand gallons worth,  a reseal is out of the question and some of these tanks were assembled in the late sixties.  I don't suscribe to the opinion that old sealent is necessarily bad or that dry tanks causes much of a problem either.   We routinely run our extended range tanks empty unless needed, but when used, they don't leak.  Finally, if flying very heavy weight ops making tatical landings in combat conditions at 750 thousand pounds gross weight dosen't make a tank leak, landing on grass with a Mooney isn't going to either.  Just my opinion. but I just don't see spending lots of money fixing a leak. 


All this being said, if you can get the leak fixed and feel better about a reseal as to a patch, go for it.  I really like the paint shop's willingness to repaint the area.  That is a nice looking paint job and you need to be happy for a long time down the road.


What say the experienced Mooney guys, patch or reseal?


Ralph

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Quote: Piloto

Once you have opened the tank section to patch the leak may as well reseal the whole compartment. It will take no more than 20 minutes extra. This will insure that you have fix the leak and potential future leaks. 

 Why would you bother looking for where the leak is if you are just going to seal the whole thing?  Or is there more work to fixing the leak spot, like rivet work?

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that's a good point, but most leaks are usually caused by a failure of the sealent as to a structural or sheetmetal problems.  Your choice is to reseal or patch.   A full reseal could still leak, a friend of mine flew from Dover to Florida  three times to fix his full reseal and it was AFTER the new paint.  A full reseal is much more invasive to your new paint.  A patch job, however, requires you to find the leak and can usually be fixed by removing only one access panel.  You might want to chat with your paint shop and see a touch up paint job is going to look as good as it looks now as some paints are much harder to blend repairs;  epoxy paints can be real tough.  Also, look into your tank filler with a flashlight and if you see a red color on the floor of the tank, it probably is a 1005-L rubber top coat used to protect the sealent.  This must be removed to insure proper adhesion of any patch, then a new top coat applied. 


Ralph

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  • 12 years later...

By Jove!  I think we have found it....   :)

MS’s first thread...

Probably not exactly the first thread... as that had some welcoming paragraph...

But it is definitely written by the first thread writer...

 

Screws under the wing walk are usually the first to leak...

As a new Mooney owner, you will find there is a strengthened area with a support that flexes the least...

+1 on using the right sealant... plenty written about it around here...

+1 on using the right solvent for cleaning up the blue stain...

+1 on using the right gritty stuff if you are repairing the wing walk material...

 

More details can be found by searching...

Best regards,

-a-

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22 hours ago, Chainfire said:

I have a M20j with one screw leaking right in front of the airplane door where everyone steps. 
 

what sealant would you recommend to seal the one screw?

 

thanks in advance 

Maxwell has recommended Permatex 3 for that.   You can pick the wing walk material off of the screw with a small steel pic, just to remove the stuff from the head of the screw to get a screwdriver in it.    Remove the screw, try to carefully dig out any remaining sealant from the screw hole.    Clean the screw off, put some permatex 3 on it, and put it back in.   Repair done.

 

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  • 4 weeks later...

I am a new Mooney owner that is trying to restore a bird that has sat for 15 years.  The tank was resealed in 2001, and the sealant looks good.  I put fuel in it and it is dripping on the underside edge near the landing gear.  So I was thinking I would try to patch it first.

I read the DMax procedure, and the Flame Master sealant is what he uses.  Where do I get that?  I found some CS3204 on aircraft spruce, but no CS3330.

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14 minutes ago, Brian Coate said:

I am a new Mooney owner that is trying to restore a bird that has sat for 15 years.  The tank was resealed in 2001, and the sealant looks good.  I put fuel in it and it is dripping on the underside edge near the landing gear.  So I was thinking I would try to patch it first.

I read the DMax procedure, and the Flame Master sealant is what he uses.  Where do I get that?  I found some CS3204 on aircraft spruce, but no CS3330.

This isn't a recommendation - just a quick Google result:  https://www.skygeek.com/flamemaster-cs-3330-cl-low-adhesion-sealant.html

Maybe give DMax a call and ask about sourcing sealant.  Important to be sure it's relatively fresh material.

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11 minutes ago, Brian Coate said:

I am a new Mooney owner that is trying to restore a bird that has sat for 15 years.  The tank was resealed in 2001, and the sealant looks good.  I put fuel in it and it is dripping on the underside edge near the landing gear.  So I was thinking I would try to patch it first.

I read the DMax procedure, and the Flame Master sealant is what he uses.  Where do I get that?  I found some CS3204 on aircraft spruce, but no CS3330.


Brian,

There are two versions of the sealant... they get used for different applications... one is for the tank seams... the other is for the inspection panels....

This way, you may be able to remove the inspection panel when needed...

If you can’t find the two different products... it would be time to make a phone call...

Another product is a top coat... not sure if the top coat is still being used... it was redish in color...

PP thoughts only, not a mechanic...

Best regards,

-a-

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I avoid Sky Geek when possible but I ran into the same situation a few months ago so I ordered all the Flame Master Sealants including CS3330 from them.  Order was processed and shipped on time.  I had a bad experience once with Sky Geek (slow shipping and no communications) but they came through this time. 

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Sky Geek has had a history of aggregating orders to improve their discount on larger bulk orders...

Its been a while since I have heard of any complaints about this particular type of problem...

But, be sure to get an expected delivery date... now you know their game...

Best regards,

-a-

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