Mooney tank/tank re-seal questons

Bill

Touchdown! Greaser!
Joined
Mar 2, 2005
Messages
15,105
Location
Southeast Tennessee
Display Name

Display name:
This page intentionally left blank
  1. Is it normal for a Mooney tank to weep slightly, or should it be totally dry?
  2. How long does a tank seal normally last?
  3. What options are available when having a tank re-sealed?
  4. What does a re-seal normally cost?
Thanks all.
 
It should not weep. At all. Although many owners put up with a little blue spotting. In my book, a drip or the smell of fuel in the cabin is a grounding item.

A reseal lasts 10-15 years, but it varies greatly depending on who did the job the last time. There is also some concern that hard landings and operating from rough/grass fields may contribute to leaking due to the wing flexing slightly.

To reseal properly, you have to scrape/grind off every bit of old sealant while working through the small inspection holes. It is very labor intensive and costs $8000 or more to do right. When faced with minor leaks, as in a little blue staining at a rivet or nutplate, there are those people who will dump more sealant at that spot. Trouble is, that may not be where the leak is actually occurring. If you seal it from the outside or just remove a screw, glop on some sealant and reinstall the screw, the leak may just move to a new spot.

Then there are bladders. Some owners opt to put in bladders rather than reseal. It costs you fuel capacity and useful load. I sold my Mooney a while ago, but as I recall the bladders weren't a panacea either. I had my wings sealed done by the late, great Charlie H. at Wet Wingologists and was happy with the job he did.
 
Bill, I invite you to join the Mooney Mailing List at www.aviating.com/mooney - a terrific mooney-specific resource.

As Ken said, a good reseal job is a lot of work, but when done correctly should last a long time. There are only a few shops that do it "right" and stand behind their product.
 
Someone told me there are also rigid tanks that can be installed in the Mooney wings, but don't know it would be done other than to disassemble the wing, install the tank and reassemble the wing.
 
Mooney tanks should be tight. Seeps around rivents imply hard landings and ovalized rivet seats. Seeps between leaves definitely mean sealant is coming off.

Have owned two Mooneys. The late great Charlie Hinojosa, the first airman who I helped back to a third class medical after MI, did a heckof a job sealing my turbo bullet- it was five figures and he had to disassemble station 48 to get it stopped.
 
NC Pilot said:
Someone told me there are also rigid tanks that can be installed in the Mooney wings, but don't know it would be done other than to disassemble the wing, install the tank and reassemble the wing.
You're referring to the bladder system. Here's a link to one compnay that makes them:
http://www.onaircraft.com/Mooney.htm

For some models this is a good choice. Overall cost with installation will be about the same as a strip and reseal job. Ken mentioned that they cost you fuel capacity. In the past that was true, but you'll see on the web page that they addressed that problem.

If you're looking at Mooneys, if it already has a weep or seep, be prepared to spend a lot of money and have weeks of downtime to have it fixed. A plane with a recent reseal commands a premium.

Jon
 
Last edited:
4CornerFlyer said:
You're referring to the bladder system. Here's a link to one compnay that makes them:
http://www.onaircraft.com/Mooney.htm

For some models this is a good choice. Overall cost with installation will be about the same as a strip and reseal job. Ken mentioned that they cost you fuel capacity. In the past that was true, but you'll see on the web page that they addressed that problem.


How much usefull load will you loose with a bladder system?
 
4CornerFlyer said:
Overall cost with installation will be about the same as a strip and reseal job.

First, the parts cost alone for an O&N fuel tank bladder installation on an M20J is $7450, which is roughly the high end of a two tank reseal job. The labor costs (40 hours estimated by O&N) is ~$2800 more (assumes $70/hour shop rate, YMMV), which puts bladders in the 1.5-2X price versus a reseal. You can get a tank resealed for ~$1.5k if you are willing to personally do the work the A&P absolutely hates (gouging skin off your arms and knuckles removing the old sealant). FWIW, I don't make $70/hour after tax, so it is well worth my time to take one day per tank off work and strip the old sealant myself.

Second, it isn't mentioned in the O&N material you posted, but the bladder tanks do inflict a weight increase so useful load is impacted if bladders are installed. The reseal option has no such weight penalty.

Third, based on various owner reports I've read the lifetime of the average bladder installation isn't much different versus the lifetime of a good reseal. IOW, O&N might claim that bladders are "the permanent solution to wet-wing leaks" but you need to read that claim carefully. IOW, the bladders will eventually leak just like wet wings will eventually leak, but technically with the bladders installed you don't have a wet wing anymore...so when the bladders eventually leak you don't have a wet-wing leak...so technically your wet-wing leaks have indeed been permanently solved--trouble is, your Mooney fuel tank leak issues are not permanently solved. See the O&N product warranty period (5 years).
 
Last edited:
I have wet wings on the IAR.

The previous owner never completely filled the tanks because the rudimentary fuel vent system would cause problems if you didn't leave an expansion space in the tanks during storage and would easily overflow during fueling if you weren't careful. I suspect the ROAF did the same because the first time I completely filled the tanks for a long x-c I got staining that indicated the seams along the top of the wing spar were weeping. Inspection by my mechanic found the existing sealant along the top of the spar was cracked in several places meaning it probably got hard over the years from the air gap.

Knowing that aging Mooney's had a reputation for weeping tanks, I looked at sending it to a Mooney dealer/maintenance facility in TX which had a good reputation for correcting fuel tank problems right the first time. They even have a publication on the subject.

http://www.donmaxwell.com/MAPA_TEXT/FUEL%20TANK%20REPAIR%20OPTIONS/FUEL_TANK_REPAIR_OPTIONS.HTM

There's some discussion on the reseal vs. bladder choice included.

When my mechanic got wind of my intentions he informed me he had plenty of experience sealing tanks on DC-3's and Beech 18's and such and said he could do mine as good as anyone. And so he did. He took a day to clean the tank, another to install the sealant, and one more to let it cure at hangar temperature before we put the fuel back in. He used a high dollar polymer (~$80/qt I think) that looked like dried Silly Putty when cured. It put a stop to the tank weeps and the lingering avgas smell in the cabin.

So if you need a tank resealed find someone who makes a living doing them. The fellow in TX is highly recommended if you can't find someone local.
 
The Mooney maitenance manual has guidelines for allowable seeps so it isn't instant grounding. But when it starts you better start making plans.

I just had my right side resealed at Willmar aviation for $3600. It is the hard side so both would be around $7000. Their process is chemical and takes one week. There was minor damage to the paint around one access panel.

I decide on them over baldders and scraped shops. Mooney factory licenses the process. But each method has pros and cons.

http://www.willmarairservice.com/
 
Anthony said:
How much usefull load will you loose with a bladder system?

Anthony,

I don't remember the exact numbers but it is about 5 or 6 pounds per bladder. I have 3 bladders per side for a total of six and IIRC I lost about 35 pounds of useful load. For my early C model I ended up increasing my fuel capacity by about 6 pounds. Note that I don't trust any partial fueling methods with the bladders so I ended up loosing another 36 pounds from the "cabin load" at the same time. When the kids are older I will probably add the new 4th bladder per side option to my aircraft.

The work to put in the bladders included new fuel caps that replaced the old thermos style caps.

I had the work done at O&N and was very pleased with the results. At the time I remember thinking that the cost was about $1,000 more than a reseal. When I did the research I spoke with two fellows who have had their bladders for over 10 years at the time. Neither had any leakage problems.

Len
 
Capt Kirk said:
Anthony,

I don't remember the exact numbers but it is about 5 or 6 pounds per bladder. I have 3 bladders per side for a total of six and IIRC I lost about 35 pounds of useful load.

That's not too bad Len. My wife wants me to get an M20J/201 instead of upgrading the Tiger's radios for IFR, so I've been following these threads with interest. While I agree with her for the extra speed, range and service ceiling, I just don't know if I want to sell the Tiger as I really like it, and having a fleet of planes ain't an option.

I guess the bottom line with considering any Mooney is to make sure the tanks have been resealed or bladdered. If not, either the purchase price or your budget should reflect the added potential expense.
 
Last edited:
Anthony said:
I guess the bottom line with considering any Mooney is to make sure the tanks have been resealed or bladdered. If not, either the purchase price or your budget should reflect the added potential expense.

From what I've read the rule of thumb is anything over 5 years on a re-seal is gravy. If you're going to look at a plane ask that the tanks be filled when you get there. Ken mentioned the smell of fuel in the cabin. That was the first tip off in my plane. My plane had been in AZ for several years. The first winter here the seals went.

Len
 
Anthony said:
I just don't know if I can sell the Tiger

Why not?

I mean, if you're having that much trouble, you can just give it to me. I'd be happy to help out. :yes: :D
 
Back
Top