Thanks for the note. I've checked my vent tube and think it's in the
right place. My fuel caps are not original and I get a small amount of
blue streaking on the right wing aft of the cap. We've diligently
checked out the gaskets and the metal ring around the top of the tank
for leaks. Everything seems to be in place. So that got me wondering
if the vented cap might be allowing air in both directions, and I
wondered it that was the way the cap should function. Maybe it
requires a half-vented cap. I have a Cessna parts book but couldn't
tell.

Dale