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Fuel leak on a 172 during a preflight I almost skipped
Last Tuesday I was rushing a preflight on a 172 at a small field outside Reno because the rental line was backed up and the owner wanted it out fast. I caught a faint fuel smell near the left wing root and found a seeping O-ring on the quick drain, dripping maybe a drop every 30 seconds onto the hangar floor. I grounded the plane right there, grabbed a bucket, and told the owner it wasn't going anywhere until we swapped the valve. He pushed back for about 10 minutes saying it was fine, but a drop every 30 seconds adds up fast. Anyone else deal with a quick drain that only seeps when the tanks are full? Trying to figure out if that's just age or a bad batch of O-rings.
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avery7214h ago
Quick drains seeping only when tanks are full is actually a pretty common thing, so you're not crazy for noticing it. The O-ring sits right at that valve seat, and with a full tank there's more head pressure pushing fuel down against it, so a worn ring that looks dry with half tanks will start weeping. On a 172 it's usually just age and crud more than a bad batch, but heat and old rubber don't help. The tell is whether it drips steady or stops once the level drops, and yours sounds like the classic worn ring. Good call grounding it, a drop every 30 seconds is like a cup an hour, that adds up over a long cross country.
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