Was chasing a fuel leak for two days until an old timer showed me the soap bubble trick on the wing tank seam

Christopher Hill · 2026-09-10T16:10:08.565871+00:00

Last month I had a slow fuel weep on a Cessna 172 that only showed up after the plane sat overnight in the hangar. I pressure tested the tank, checked every fitting twice, and even replaced the cap gasket, but the blue stain kept coming back near the outboard rivet line. An A&P with 30 years on type walked over, mixed up some dish soap and water in a spray bottle, and had me pressurize the tank to just 0.5 psi with a shop vac on blow. Within ten seconds we saw a stream of tiny bubbles right at a rivet I'd wiped clean three times and swore was dry. The soap found it in under a minute after I burned two days poking around with a flashlight and mirror. Ended up re-sealing that rivet and the leak is gone. Now I keep a spray bottle of soapy water in my box, has anyone else had good luck finding seeps this way or do you have a better method for pressurized checks without over-stressing the tank?

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Was chasing a fuel leak for two days until an old timer showed me the soap bubble trick on the wing tank seam | Aircraft Mechanics - Guest Forum