The Cessna 120-140 Association Forum

I have a 1950 140A and recently I noticed staining behind my fuel caps continuing down the top of the wings. I wiped it clean and after my flight last night immediately checked after landing and sure enough fuel is being sucked out. But I can't determine if it's coming from the gaskets on the fuel caps or maybe the fuel cap vents. The caps go on tight and gaskets are not visibly broken or deformed. Any recommendations for trouble shooting?

My best guess is gasket, especially if it's relatively recent. Another possibility would be plugged vent/vent line...if I'm remembering correctly that there is a central/top vent(?) on the A. Otherwise, I wouldn't think that there's anything "mechanical" with the cap that could cause it, 'though I don't have an "A" cap handy to confirm. Let us know what you find. Mac

I would suggest you read the article on fuel systems and caps in the "Neal Wright Technical Articles" section of the Forum Archives. Make sure your caps are correct and the vent system is working as designed.

I've got two 140A's and have had the same issue you're experiencing. If you take a look at the 140A Parts Book for the fuel tank installation you'll notice in the drawing that there are (2) two gaskets used in the filler neck system on the aircraft. One is p/n 0533531 which is the gasket installed under the top skin that covers the fuel tank. That gasket seals the top skin between the filler neck adapter, p/n 052359 (that bowl looking metal cup that surrounds the filler neck) in order to keep debris/dirt from entering the fuel tank area. Below the filler neck adapter (p/n 052359) is another gasket p/n 0523532 that seals the adapter to the top of the fuel tank. It has been my experience when I had fuel leaking on the top of the wing near the filler neck that the bottom gasket (0523532) was bad, and was causing the fuel to siphon slowly up past the adapter and onto the top of the wing. Symptoms look like the fuel cap is leaking, but that may not be the case. I'd opt for checking/replacing that bottom gasket (0523532).

...don't know if this may help, but here's a pic (I believe) of the 140A filler cap/area:

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...oh well, I tried. PM me & I'll try to send via email if you think it might help.
Mac