First, a disclaimer is in order. I do not recommend the procedure about to be described due to the potential danger. Having said that, I am conducting a leak test on about 50% of the fuel tank using actual avgas. I did this same test on my port fuel tank before sealing the baffle and it exposed no leaking rivets on the forward half of the tank. This gave me added confidence before installing the rear baffle.
To accomplish the test, I siphoned 5 gallons of avgas from my Piper Archer's tank and transferred it into my partially completed starboard RV tank. I then added another 5 gallons of regular autogas which filled the tank to the line shown in picture two below. This 50/50 gas mix retains the blue dye of the 100LL avgas so any seeping rivets will show the blue stain. This procedure was carried out in a well ventilated space (front of garage with door open) to reduce any fumes. The tank was left to sit for 24 hours and inspected for any leaks. None were found. The fuel was then transferred into my Chrylser.
Again, this procedure is risky so it is not recommended. On the positive side, however, it does confirm the integrity of the rivets from the mid-point of the tank to the extreme leading edge and these are areas prone to leaking. The rivets and ribs from the mid-point back are much easier to inspect. After installing the rear baffle, access plate, and fuel sender I will do the normal soap bubble and balloon test as was done on the port tank.
