What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Fuel tanks venting through caps

00Dan

Well Known Member
I know the fuel tank vent line design in the -4 makes it exceedingly difficult for any fuel to exit through the vent. What I’m seeing is my tanks are venting fuel through the center of my caps after a fill up. I have the old black o-ring caps, for reference.

Is this a common problem? Should I look at rebuilding my caps or is this something I’ll just have to live with due to the vent line design?
 
Rebuild the caps

The caps will leak as they age. Rebuild, keep lubricated and maintained. The vent system if built correctly will do its job. If your plane is sitting unlevel, you may still get some out of the cap, but dont overfill past the bottom of the cap flange. Remember, if fuel comes out the cap, rain goes in the cap. The vents are critical to continued fuel flow to the engine, and you need to be sure they are open and unobstructed , but the cap should be completely sealed. The rebuild is simple and I keep spare O-rings and the cam pivot on the shelf ..cheap insurance.
 
The caps will leak as they age. Rebuild, keep lubricated and maintained. The vent system if built correctly will do its job. If your plane is sitting unlevel, you may still get some out of the cap, but dont overfill past the bottom of the cap flange. Remember, if fuel comes out the cap, rain goes in the cap. The vents are critical to continued fuel flow to the engine, and you need to be sure they are open and unobstructed , but the cap should be completely sealed. The rebuild is simple and I keep spare O-rings and the cam pivot on the shelf ..cheap insurance.


I’ve noticed a similar issue recently. Where does one find the part numbers, etc for the parts you mentioned?
 
More than one O ring

Those seeing "venting out the fuel caps" have bad O rings as the Usher caps are not vented. There is a small hidden O ring around the shaft going through the cap in addition to the large one you can see when removing the cap. It is likely your small O ring needs replacement. You will have to dismantle the cap to get to the small O ring.
 
O-Ring size

Are the O-rings from Van's Viton? Their website does not say, and the description states "The brown O-rings are generally auto fuel resistant, but their tolerance for the newer oxygenated auto fuels is unknown". If they were Viton, this statement would not be necessary.

Does anyone know the sizes of the two O-rings? Would be simple enough to source.
 
Along the lines of the o-ring discussion, what is it about the brown o-rings that makes them incompatible with the old caps? Did the castings change? Van’s website says the new caps will fit any receptacle so it can’t have been outer dimensions that changed.
 
Back
Top