While working on the R spar, Marc came over to help figure out the tank issues. He's also an engineer and I wanted a fresh pair of eyes on the problem. He agreed that there should be no leaks based on my procedure and his visual inspection. Back to testing: we split up the tasks of one person pumping and the other spraying bubble soap, but never saw any bubbles. We finally took the compressor and blew air into the tank. We could feel a breeze on our fingers on the inboard edge (with all of the connections) but couldn't make any bubbles appear nor feel our way to the leak.
Rather than using expensive, toxic, smelly and flammable avgas I decided to do an old fashioned test. We filled the tank with water from the hose. Viola! The Proseal around the fuel sender leaks like a sieve! Water streamed from the entire circumference. Mystery solved.
This also validated my gut feeling that it was a systemic issue. Recall that I used left over Proseal that had been in the freezer. While working with it, it was appropriately sticky and gummy and I thought it was OK, but apparently it was by then too viscous to actually flow when I tightened down the fuel sender plates.
I'll order some more Proseal (or B2 sealant as it is now known) and re-do the senders when it arrives. I'm feeling much more optimistic that we'll get something that is water tight next time.
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