Deciding when to reseal/bladder vs patch

[Huckster79]

1968 m20f.  Pretty good blue stain under pilots wing.  Got some good info from the vintage Mooney fb group- but was hoping for some more in depth conversation on figuring out a “theology” of when to go for a full reseal or bladders vs a patch? 
 

how have you all made that decision? I’ve only owned it since April, does one patch for a hoped one off that will hold, then see if it’s just going to be constant chasing? Until one gets to know the bird?   I’m nice they start they don’t stop?  does it depend on where n how big it is?

This is a new area of ownership for me, my old c140 just had plain tanks. So much like deciding when to overhaul… looking for some theories on the “when” to do go all out vs patch? 
 

[N201MKTurbo]

First off, there is no such thing as a patch. You can repair the tank sealant according to the instructions in the service manual.

That is a typical leak. it can be caused by a leak anywhere in the front of the tank. You can get a better idea if you look in the inspection panel and see  where it is coming from.

You cannot judge the quality of the sealant by looking at the outside of the tanks.You have to get in the tanks to evaluate it. And a complete reseal doesn't guarantee anything. The last time I assisted someone with a repair, it was recently resealed by one of the highly respected shops.

A properly done repair is as good, or better than the original sealant. The leaks are usually due to a minor error in the sealant application, not a failure of the sealant itself.

When in the tanks, and fixing the leak, you can tell if the sealant is bad if it peels off easily, is soft and uncured or hard and brittle. If it is still rubbery and well bonded, it is a waste of money to do a complete reseal.

[Hank]

The Maintenance Manual has size specifications on what is an acceptable leak; anything more will.need some sort of repair.

Questions to ask:  when were the tanks resealed last? Is there evidence of previous patching inside? Is the sealant in good shape except for the leaking area?

My tanks had been patched several times when I did a complete reseal. The original sealant was then 50 years old. Some was reported to be crumbling and sandy-like. It was definitely time.

To tell, you'll need to fly a tank empty or drain it, then look inside.

[Shadrach]

That can likely be repaired. The cost to remove and reinstall the inspection panels is nominal. I have been into my tanks three times in the last 20 years. They were supposedly stripped and resealed in 1999. As it turned out, they were only mostly stripped and resealed. There were still areas of original sealant. Over the years I have removed the remainder and repaired as necessary. At this point, I look at the tanks as an area that will need minor mx every five to seven years. All of my issues have been annoyances rather than airworthiness issues (per the maintenance manual).

Internal source of failure is rarely obvious to the naked eye. The best way to determine location is to spray the inside of the tank with soapy water, tape plexiglass over the access panels and observe the inside of the tank under vacuum. The best way to fully observe the tank interior under vacuum is to place mirrors and lights inside during the process.

[Ragsf15e]

The one on the left wing looks like it’s leaking internal to the wing and then coming out the drain hole. I’m pretty sure the maintenance manual says that is an airworthiness issue. That one is probably driving a sooner rather than later repair or reseal.

[dennis riz]

have you figured how much fuel you are losing?? I have similar leak and at one point missing 25-30 gallons of gas trying to figure out it if it leaks that much, I dont see fuel on hangar floor

[Shadrach]

On a side note, whoever did the sump relocation AD on the OP's bird did a nice job.

[Skates97]

At what level does it stop leaking? That gives you an idea where to look for the leak when you open up the inspection panel.

Before I bought my plane it had a complete reseal done by Wetwingologists in FL. The right tank, if I filled it, would get a leak like that. It would stop once it was at about 22 gallons in the tank. I called Wetwingologists and they were happy to fix it under warranty but I was on the other side of the country. He said it was likely a quick fix as sometimes there will be an air bubble in the sealant that pops and dries leaving a pinhole.

I measured how far down the fuel level was when it stopped leaking to give myself an idea where to look. We drained the tank, opened up the inboard inspection panel on the bottom, and I looked around the sealant at about the level we had measured and sure enough, found a pinhole in the sealant. Applied sealant there and it hasn't leaked since.

Knowing at what level it stops leaking will give you an idea where to look in the tank for the issue. You can also follow the Don Maxwell method.

 

Fuel Tank Repair.pdf

[dennis riz]

thanks for info that makes sense, if fuel is below tabs seems to hold up. I will play around with adding small amounts

[Shadrach]

34 minutes ago, dennis riz said:

thanks for info that makes sense, if fuel is below tabs seems to hold up. I will play around with adding small amounts

The only way to verify all leaks is to observe the tank under vacuum.  Even then it's a good idea to repeat the process and check again.  I usually mark any observed leaks with a sharpie and then spray again and observe.  I really don't dread tank repairs like others do. I would open up a side business if I were credentialed. It's straight forward, methodical work that yields gratifying results.

[DCarlton]

You’re lucky.  You live in MI.   You can easily fly to Wilmar for a proper reseal. I’d get on the schedule for 2025 and enjoy having the issue behind you.  

[Shadrach]

 

9 hours ago, DCarlton said:

You’re lucky.  You live in MI.   You can easily fly to Wilmar for a proper reseal. I’d get on the schedule for 2025 and enjoy having the issue behind you.  

What's a complete reseal cost these days? $9K? More? It's my opinion that a reseal is a complete waste of money and resources unless it has been determined that the sealant is deteriorating.  That determination has yet to be made in this case.

Almost any reseal situation other than deteriorating sealant will mean significantly more effort will be devoted to removing perfectly good sealant than correcting the actual problem(s).  Localized repairs are not difficult and are long lasting if performed IAW approved procedures and materials.   

Mike Busch has created a successful business whose primary service is preventing needless maintenance.  I know that's not how it's marketed precisely, but that is exactly the end game of the service being provided.  The OP is new to Mooneys and has yet to determine the cause of the leaks. Probably more prudent to determine the condition of the tanks rather than to just throw 10K at it.  Every dollar spent on unnecessary maintenance is a dollar that could otherwise be spent on enhancing safety and reliability. 

[DCarlton]

47 minutes ago, Shadrach said:

 

What's a complete reseal cost these days? $9K? More? It's my opinion that a reseal is a complete waste of money and resources unless it has been determined that the sealant is deteriorating.  That determination has yet to be made in this case.

Almost any reseal situation other than deteriorating sealant will mean significantly more effort will be devoted to removing perfectly good sealant than correcting the actual problem(s).  Localized repairs are not difficult and are long lasting if performed IAW approved procedures and materials.   

Mike Busch has created a successful business whose primary service is preventing needless maintenance.  I know that's not how it's marketed precisely, but that is exactly the end game of the service being provided.  The OP is new to Mooneys and has yet to determine the cause of the leaks. Probably more prudent to determine the condition of the tanks rather than to just throw 10K at it.  Every dollar spent on unnecessary maintenance is a dollar that could otherwise be spent on enhancing safety and reliability. 

Know anyone out West that's wiling to take on a patch?  I don't.  No one wants to do fuel tank work.  Know anyone out West that's willing to do much of anything for less than $2K and another months downtime (or more)?  I don't.  Find me someone, I'll get a patch.  For me, if there's no one in SOCAL, it's another grand in travel and logistics costs to get it patched or more.  If you take it to Texas, you get in line and probably wait months to get your plane back.  A fellow Mooney driver at my airport said I took him three months to get his Ovation out of annual in TX.  I had mine patched 15 years ago; I'm ready to get mine done for good.  The original post flies an F.  Really think the sealant is still good?  If you schedule with Wilmar, you're out to 2025; plenty of time to find a patcher... if you're lucky.  

[Shadrach]

10 minutes ago, DCarlton said:

Know anyone out West that's wiling to take on a patch?  I don't.  No one wants to do fuel tank work.  Know anyone out West that's willing to do much of anything for less than $2K and another months downtime (or more)?  I don't.  Find me someone, I'll get a patch.  For me, if there's no one in SOCAL, it's another grand in travel and logistics costs to get it patched or more.  If you take it to Texas, you get in line and probably wait months to get your plane back.  A fellow Mooney driver at my airport said I took him three months to get his Ovation out of annual in TX.  I had mine patched 15 years ago; I'm ready to get mine done for good.  The original post flies an F.  Really think the sealant is still good?  If you schedule with Wilmar, you're out to 2025; plenty of time to find a patcher... if you're lucky.  

I sometimes to neglect to allow for the different degrees to which people are plugged into their maintenance communities and or willing to be hands on. I forget that there are those who’s choices are limited. I’m on the eastern seaboard and have a number of mechanics that will supervise me doing this kind of work. I’m pretty sure if I were in California the scenario would be the same. That being said the shop on my field will and has done fuel tank repairs. 
The age and model of his aircraft is not relevant. The age and condition of the sealant is. 

[dennis riz]

agreed, I am gonna fly the plane to use the gas thats in it and my local A&P is going to perform the leak teat, In my case the tanks were resealed by wetwing in oct of 2012,the

warranty was 7 years. I was quoted 5600 a wing for a reseal. Hoping my A & P will be able to just fix the leak.

 

[Shadrach]

1 hour ago, dennis riz said:

agreed, I am gonna fly the plane to use the gas thats in it and my local A&P is going to perform the leak teat, In my case the tanks were resealed by wetwing in oct of 2012,the

warranty was 7 years. I was quoted 5600 a wing for a reseal. Hoping my A & P will be able to just fix the leak.

 

Ouch. Seems like the price goes up about $1000 every 5 years.  I think it was ~$2000 a side when I started flying the Mooney 20 years ago. 

[DCarlton]

3 hours ago, Shadrach said:

I sometimes to neglect to allow for the different degrees to which people are plugged into their maintenance communities and or willing to be hands on. I forget that there are those who’s choices are limited. I’m on the eastern seaboard and have a number of mechanics that will supervise me doing this kind of work. I’m pretty sure if I were in California the scenario would be the same. That being said the shop on my field will and has done fuel tank repairs. 
The age and model of his aircraft is not relevant. The age and condition of the sealant is. 

To me, what you describe are the good ole days.  Long gone where I live.  Currently, you're lucky to have someone local willing to do your annual.  My mechanic retired.  His two younger well trained employees left for higher paying jobs.  Everyone else is saturated with flight school aircraft or they're making big money off of jets.  Get in line.  For me, screwing around with a patch that may or may not work is just wasting what flying years I have left.  

[Shadrach]

13 minutes ago, DCarlton said:

To me, what you describe are the good ole days.  Long gone where I live.  Currently, you're lucky to have someone local willing to do your annual.  My mechanic retired.  His two younger well trained employees left for higher paying jobs.  Everyone else is saturated with flight school aircraft or they're making big money off of jets.  Get in line.  For me, screwing around with a patch that may or may not work is just wasting what flying years I have left.  

I totally get that. Money vs time calculations change at different points in life.  Maintenance relationships take time to build. I am guilty of taking that for granted. 

[PT20J]

As @N201MKTurbo said, there is no such thing as a patch. There is such a thing as a repair, and as @Shadrach said, if the sealant is not deteriorating and has good adhesion except for the location of the leak, there is no reason that a properly done repair will not work. My 1994 J was repaired twice by Mooney under warranty and once by a previous owner many years ago, and it doesn't leak. In 1987, I purchased a 1978 J and one tank was repaired by the previous owner and it never leaked in the seven years I owned it.

Repairs are expected -- that's why there is a procedure in the service manual. But, it has to be done right. Find a shop like Maxwell that has done a bunch of them.

[DCarlton]

7 minutes ago, PT20J said:

As @N201MKTurbo said, there is no such thing as a patch. There is such a thing as a repair, and as @Shadrach said, if the sealant is not deteriorating and has good adhesion except for the location of the leak, there is no reason that a properly done repair will not work. My 1994 J was repaired twice by Mooney under warranty and once by a previous owner many years ago, and it doesn't leak. In 1987, I purchased a 1978 J and one tank was repaired by the previous owner and it never leaked in the seven years I owned it.

Repairs are expected -- that's why there is a procedure in the service manual. But, it has to be done right. Find a shop like Maxwell that has done a bunch of them.

"spot repair" ?

[Jsno]

I have just started a fun reseal in one of my tanks.  I tried patching areas but leaks kept developing.  This is a very tedious job and will probably take me one to two months part time.  I have found through discussing with professional aircraft fuel cel mechanics and an engineer at work that heat is what damaged the sealant.  So if fuel is not covering the sealant, the heat will cause it to deteriorate.  That is probably why your tank leaks above the tabs.  Most folks don't keep their tanks absolutely full.  It is probably an area far outboard or the upper spar.  I have found a six inch area where the sealant was completely missing on the upper front spar on mine.

Another problem is that my tank has Buna slosh coating over the sealant.  Apparently it was done a second time as well to attempt to seal the leaks.  It did no good.  It makes removal much more difficult as Polygone does not touch it unless it gets on the sealant underneath.  I actually use a pick to lift as much as I can off before scraping.

I think you should open up the tank and look for areas on the upper spar, and outbid and see if that solves your problem before a full reseal.  If you are considering bladders, I have found that they are expensive, add weight, and the tops will also dry out if not kept full so I have opted for sealant.  I think most Monney owners do not keep the tanks full because it will cut into your useful load.

 

Like stated above, make some plexiglass panels, apply about ten lbs of vacuum and look for bubbles.

 

 

[Jsno]

One more thought on scraping sealant.  If you scratch the metal be sure to etch and alodine the area or you will get corrosion under the sealant.

[EricJ]

39 minutes ago, DCarlton said:

"spot repair" ?

aka, "patch". 

[Shadrach]

40 minutes ago, DCarlton said:

"spot repair" ?

[Shadrach]

4 hours ago, Jsno said:

One more thought on scraping sealant.  If you scratch the metal be sure to etch and alodine the area or you will get corrosion under the sealant.

You should be using non marring tools for sealant removal. I use a scroll saw to cut custom shaped tools from plexiglass then smooth an area for a hand grip on my grinder.