Resealing vs. Bladders – Fuel Tank Repair Options

By Don Maxwell
Published MAPA, Volume 22 , Number 8 ~ August/September 1999

The calls are pretty much the same. “I have a leak under my wing, or a leak on top of the wing when it’s full, or I smell fuel in the cockpit; what would you charge to seal my tanks?”  The answer is, it’s hard to say with out seeing the plane, and a reseal may not be needed.

Repair or Reseal
The worst type of job I can think of in this business is resealing fuel tanks. Fortunately, not all leaks require a complete reseal. Most articles I’ve read about sealing tanks make it sound so mysterious, and only those with supernatural abilities could seal one properly. In reality, I’ve found most leaks are fairly easy to locate, and repair. The tanks are accessible from all six sides, and the blue dye in the fuel will pinpoint their origin on the outside of the tank. Removing the access panels above the suspect area will usually reveal an indication of where the leak originates in the tank. At this time, we evaluate whether this is a localized problem, such as a loose rivet or pinhole (fig.1) in the sealant, or a breakdown of the sealant into a chalk like material requiring a major re seal..

Panel Leaks
Most of the leaks we see are inspection panels. In some cases we may just tighten the screws on the panel or remove a panel screw (fig.2) that shows signs of leaking, apply some sealant to the threads and replace it. A panel is a little more difficult. If it’s a bottom panel leaking,(fig.3) I will remove the top panel, and seal it from above. To remove a panel requires patience. First drain the remaining fuel and remove the screws that secure the panel. Next mask the panel and the area around it with masking tape. This will protect the paint from damage. Do not beat on the panels. The panels are glued to the underside of the wing with the same type of sealant used to seal the tank. Take a very thin putty knife and work the blade between the panel and the wing. I use a rubber hammer to work the blade around the panel, sometimes several times, until the panel releases.  With the panel removed I use a flashlight to examine the interior condition of the tank . If the leak appears to be localized, and the rest of the sealant is pliable, I reseal the area, seal and replace the panel. I recommend leaving the tank empty for at least three days.

Cabin Fuel Smell
Cabin leaks are probably the easiest to locate and repair. First, I remove both front seats, carpet and the side panels. In some cases it may just be a leaking gasket on the fuel gauge  sending units and tightening the screws is all that is needed. The source of the leak can be located by the fuel stain from the blue dye in the fuel. I routinely repair these leaks on the inside of the cabin if there are no other leaks requiring removal of the wing inspection panels. Usually the carpet is saturated with fuel and the smell will remain until the carpet is replaced.

Full Tank Leaks
Most deterioration of the fuel tank sealant that I see is in the top of the tanks. Apparently, tanks that are not kept full while the airplane is inactive, tend to have top leaks. It is not uncommon to remove long strips of sealant from the top of tanks in this condition by hand. These leaks usually cover a wide area and are harder to reseal because of their location.

Reseal or Bladders
I’m often asked, “what do you think about bladders?” Until recently I’ve answered that they were for Bonanza and Cessna drivers, or that mine wasn’t big enough! Bladders were new to Mooney’s’, and my thinking was that if bladders were so good, the factory would have installed them. Another factor was you could still get a strip and reseal for around $4000.00. Recently, we have installed the O&N bladder system in some of our customers Mooney’s. I must admit, I was impressed with the ease of installation, and the accessibility of the individual bladders if removal becomes necessary. Installed price for bladders in a “C” “D” “E” or “G” is approximately $6500.00 depending on your shops labor rate. I checked with some tank shops and found that a strip and reseal runs approximately $5500.00 for the short bodies, $6500.00 for the “F” and “J’s” to $7700.00 for the “K’s” thru “M’s”.

Plus vs. Minus
Although I would prefer a good strip and reseal job, there are some very positive aspects of the e bladders. Stripping and resealing tanks is a very labor intensive operation that I find employee’s don’t want to do. I have spoken with several individuals that are trying various chemicals to remove sealant and one that was experimenting with a laser . But for now, with only a few shops willing to scrape tanks, I see the price for this service will only increase. Most warranties are for five years, and then the possibility of another reseal. Bladders are individually removable, repairable and on the short bodies add about three gals of fuel capacity. The one downside, that I see to the bladder system , is that on the longer bodied “F’s” and “J’s” is that nearly 10 gals of fuel capacity is lost. Most of my flying has been in an “E” model and it’s 52 gal capacity has always exceeded mine. A recent online discussion with a couple of our “online family” aircraft salesmen was a draw. One felt that the reduced fuel capacity would hurt the aircraft resale value. The other claimed to have sold dozens of aircraft and that the bladders had enhanced the aircraft value.