Beginning to wonder if I dreamed this, but it seems to me I read that we are supposed to put a 1/16 hole in the top of the fuel cap. Static, full tanks, tight and dry, Post flight, fuel stains on under side of wings from sump to back of wing. Sump nozzle shows no leakage. Any Ideas,? it sat with full tanks for 2 months, and no leaks.
Thomas - I used the Zenith caps for the first 70 hours and had fuel stains on top of the wing. I replaced them with Cessna caps and fuel is no longer exiting on top of the wing. As far as the sump CAV drainers; when I check for water I usually wipe it off with a rag and that seems to help reduce the leakage (almost stop it). I got the idea (of the Cessna caps) from Bob McDonald on this site.
I'v had stains underneath both from the fuel sender screws and overfilling the fuel which runs inside the wing. My caps have the gooseneck forward facing vents however I like the idea of Cessna vented caps, which I think are now mandatory fittment to both sides of Cessna tanks.
Only trouble I had was when a cap got left behind on the runway, I lost most of the fuel from the OTHER side on that trip, before I stopped the crossfeed and switched to the open tank. Soon learnt its best to safety cable the caps to the tanks, so you can't takeoff without them, well without them making a lot of noise. Also do not allow others to distract during fuelling operations!
Its probably a good practice to carry a "spare" gas cap. In the event you lose one either in-flight or on the ramp it could be a trip saver to be able to retrieve a spare cap from your stash onboard the aircraft. I carry a cap that came with my kit as a spare.
I found vented Chrome gas caps for older Harley on ebay for $9 each free shipping. Bought two and they look good and don't leak like the stock ones. Go to Ebay and put in this number in the search box: 330468052118
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