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Under Seat Tank Filler Neck Baffle?

Golden Burro

Golden Burro

Member
Joined
Mar 18, 2023
I replaced my old rusty under seat fuel tank with a poly one a few years ago. The cap is original and seals about as good as it seems it can, but when I sidehill on the left side or go around a right hand turn it leaks fuel when the tank is pretty full. I've put different gaskets in the cap, but I think it still needs some venting. I was thinking about putting a viton plug with at gas nozzle sized hole in the filler neck. That would block at least some of the spillage. Anyone got a better idea? Yeah, someday I'll go to a rear tank, but thats a ways down the list.
 
You need a vent to the tank - maybe move the vent higher?
If you are sure that the gasket of the cap seals to the tank, I'd suggest relocating the vent.
Plug the vent in the gas cap with some kind of gasoline-proof putty (I've used "Liquid Steel").
Then add a nipple to the filler neck.
With a poly tank, I'd likely use a soldering iron to put a hole in the neck and thread in a brass nipple, maybe 1/8" NPT.
I'd think you could use the roll bar and send a tube of some type way up somehow.
Maybe put another nipple at the base of the roll bar and connect with a hose?
Another hole in the roll bar might be needed to admit the atmosphere to the gas tank.
 
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Get the proper cap to match the aftermarket tank. If MTS they make a cap specifically for their poly tanks. Poly tanks typically have a thicker filler neck than steel so the stock caps don’t seal well. My stock steel under seat tank with good sealing cap did the same thing due to the vented cap.
 
timgr said:
You need a vent to the tank - maybe move the vent higher?
If you are sure that the gasket of the cap seals to the tank, I'd suggest relocating the vent.
Plug the vent in the gas cap with some kind of gasoline-proof putty (I've used "Liquid Steel").
Then add a nipple to the filler neck.
With a poly tank, I'd likely use a soldering iron to put a hole in the neck and thread in a brass nipple, maybe 1/8" NPT.
I'd think you could use the roll bar and send a tube of some type way up somehow.
Maybe put another nipple at the base of the roll bar and connect with a hose?
Another hole in the roll bar might be needed to admit the atmosphere to the gas tank.
Click to expand...
I like the idea of adding a vent, but attaching it to the roll bar sounds like a bad idea unless its strictly an open top Jeep. Personally I'd run a hose into the engine compartment and put a vent high up on the firewall.
 
The only problem with the engine compartment is you'd have to go down to go up into the engine compartment.
This would result in pooling of gasoline in the low area.
If the roll bar is not a good option, maybe send it up into the rear wheelhouse?
Still not very high.
Wild idea, but actually plumb it into the rollbar, then vent the passenger side of the hoop down through the floor to the outside of the Jeep?
The hoop is pretty much a closed space that you could use as a passage for air/fumes.
 
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I found that the filler neck on Tonk was dented & the cap gasket wouldn't seal. After fixing it & orienting the cap so the vent hole is at the top I haven't had any more issues with gas leaking out the filler neck. If everything is in good condition the stock system works. Got a post on here someplace about this but I can't find it.
 
Venting to the rear wheel well is what a lot of folks here have done. Add a filter to the end. Mine is vented from the top of the filler neck down to the frame. It might dribble if i'm laying completely on the driver side but not any faster than the vented cap or a loose cap.
 
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