Chasing a phantom fuel leak on a 172 for 9 hours, was it the O-ring or the flare?

Gavin Hall · 2026-11-01T00:30:05.778666+00:00

Had a 172 in the shop for a slow fuel smell near the left wing root and figured it was a 30 minute O-ring job. Turned into 9 hours over two shifts because we kept pressure testing the wrong spot and the leak only showed up when the tank was above half full and the plane sat at an angle. Side one says always pull the panel and redo the flare fitting first, side two says swap the cheap O-rings and call it done since most of these leaks are old rubber. I'm honestly not sure which habit saves more time in the long run and I've seen both bite people. What's your go-to order on a leak you can't see, and how do you keep from throwing parts at it?

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Chasing a phantom fuel leak on a 172 for 9 hours, was it the O-ring or the flare? | Aircraft Mechanics - Guest Forum