Gas leaking out of tank vent

[NovaSF]

Hello everyone. I have a LS3 swapped 70 Nova with a basic return style system. Noticed a little fuel dripping under my car today after a little drive. Appears it was coming out of the gas tank vent (pictures). I then opened the gas cap and a bunch of pressure blew out of the filler neck. Weird. The drips stopped. Tank is about 60%full.


Clogged vent where it allows pressure to build then puke??? Any thoughts???


Thanks!

[grease]

Does the vent have a roll over valve in it? If yes, it may need to be installed vertically instead of horizontally.

[NovaSF]

Hmmmmm. Not sure. Would a roll over valve have something to do with the big washer right under the vent cylinder? Not sure what the purpose of that washer is.

[NovaSF]

Quick search..... bingo. Sure looks a lot like this.. Roll Over Vent Valve.

[dhutton]

Needs to be vertical and above the level of the tank with no dips in hose that could collect fuel.

Don

[RdHugr 68]

Rollover vents are more trouble than they are worth.

[Twentyover]

Rollover vents are more trouble than they are worth.

But required by many vintage racing sanctioning bodies

Quick search..... bingo. Sure looks a lot like this.. Roll Over Vent Valve.

Rollover check valve is frequently a ball check valve depending on gravity to remain open to vent. Mounted sideways, it's boned. So the question I'm having is why the tank is building pressure when functionally sealed and consuming fuel?

[andrewb70]

Someone didn't read their Tanks Inc. instructions :-)

Andrew

[2yellow69]

Could the pressure build up be the fuel warming up? Or the engine creating a vacuum by using the fuel in a "sealed" tank? Between the fuel warming up and the vacuum in the tank the roll over check ball might be the easiest route for fuel to escape?

A long time ago when my 69 Camaro was stock someone stole my gas cap. Well, I may have left it at the gas station. Anyway, I bought a new cap, put it on and went on my way. The next night at 2 in the morning it sounded like someone hit my car with a tennis ball and set off the alarm. My neighbors and I ran outside and found nothing. It happened a few more time during the week and my buddy and I decided to stay up and catch whoever was messing with my car. A little after midnight, while we were both looking at the car, it happened again. No one was around and nothing hit my car. The next day I started investigating and found the new non-vented cap had allowed the 30+ year old fuel pump to collapse the top of the tank. As the night cooled down the tank slowly released vacuum and the top of the tank would "pop" partially back into place. A new tank and sending unit with a VENTED cap solved the issue. It was amazing that the fuel tank was absolutely destroyed by putting the wrong gas cap on.

[NovaSF]

I guess I’ll have some questions come Monday for the dude who did the fuel system set up. Uuurrrrrgggghhhhhhhh.

Took out the valve, tested it, it’s functioning as it should. The temps here don’t swing too much in SF but there have been some highs and lows lately when I’ve been driving (~ 25 degrees), don’t know if that matters.

Gonna trim the tube a bit so there are no flat spots and it’s perfectly vertical and make a little bracket. Then test and WE SHALL SEEEEEEEEEE.

Thanks for everyone’s input, this site is very therapeutic at times as it helps from going down the rabbit hole into what the hell is wrong this time madnesss....

[andrewb70]

Also, why is there a hose clamp on what looks like an AN fitting? On the center port of the regulator/filter...

Andrew

[NovaSF]

Here’s a pic of that hose clamp

[NovaSF]

Gonna go test later today🤞

[2yellow69]

If I remember correctly, the center port is the return to tank line. It's been a bit since I've worked on my car. That fitting is probably a barbed fitting to AN.

[andrewb70]

The inlet AN adapter is loose. The one that's offset.

[NovaSF]

AndrewB70.... everything on the offset seems tight and no leaks. Am i missing something obvious??

[blitzer454]

AndrewB70.... everything on the offset seems tight and no leaks. Am i missing something obvious??

I think Andrew is referring to the gap in the hose fitting. There should be no gap like the other fitting.

[andrewb70]

I think Andrew is referring to the gap in the hose fitting. There should be no gap like the other fitting.

Yes...that.

[Hotwire]

I ended up pulling my Tanks Inc rollover valve (running their tank in my 64 Chevelle). The vents they have in the tank cause too much fuel to run up through the vents constantly triggering the rollover valve and allowing pressure to build in the tank. I've had so much pressure build it was pushing fuel out of the sending unit/fuel pump access gaskets.

If you want to keep the rollover valve I highly recommend installing a burp tank inline on the vent so that fuel will not get to the rollover valve. I plan on getting an ebay PCV catch can and converting it to burp tank duty then reinstalling rollover.

[NovaSF]

Thanks.. I’ll investigate