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Are my Fuel Tank Vents Working?

PandaCub

PandaCub

Active Member
I'm blessed to fly both an RV-14A and an -8.

When I top off the tanks on the -14A, if the day significantly heats up expanding fuel will drip out the fuel vent tube(s) onto the tarmac. This seems normal.

On the -8, though, I sometimes see blue Avgas streaks emanating from the closed fuel cap and going down the top of the wing. Shouldn't thermally expanding fuel follow the path of least resistance, i.e. thru the vents?

The engine (IO-360-M1B) has always run fine, but I'm concerned about possible fuel vent blockage. How could I test for this? Any thoughts appreciated.
 

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You can check the vents are clear by either blowing in the vents or blowing in the fill cap and having someone listen for the air escaping.
 
If fuel is getting past the filler caps, they need adjusting or new O rings.
 
DOn't know about the 8, but on the 6, fuel has to push up about a 1.5' head to get out of the vent exit. Therefore, if the cap o-rings are not sealing properly, THAT is the path of least resistance for the expanding fuel and air. It will only push out of the vent if the cap is sealing.

Larry
 
Usher Fuel Caps:

Adjustment instructions and parts shown below. Instead of fuel lube for lubrication many folks use Krytox GPL 205 grease with good results. Expensive, but the small 0.5 ounce tube will last a long time.

i-CZCx5NV-L.jpg


Parts are available from Van's:

 
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Jetmart said:
Do you lube both O-rings or just the small one?
Click to expand...

The answer to your question is contained in the first line of the instructions that you quoted in your post:
"FOR PROPER FUNCTION: If cap becomes difficult to latch, lubricate both O-rings and all moving parts ..."​
 
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