Why are my vent lines leaking?

[DynaBro]

Cars with return lines had the line connect to a nipple on the sending unit, not one or the tank vents. Hook it up properly, make sure the vent lines are clear, use a non vented cap, and try again.

Now this is interesting. So the return line is going to the wrong spot. I think they smashed the nipple on the sending unit cap to close it off though. I will get a photo. I worried this might be the case.

 

[DynaBro]

No bueno.

 

[R/T Boy 67]

I wonder why anyone would do that? I would drain the tank down, remove the sending unit and try to fix it.

 

[DynaBro]

I wonder why anyone would do that? I would drain the tank down, remove the sending unit and try to fix it.

I also have no clue but am curious to hear theories from guys who've been at this for a long time.

 

[DynaBro]

dadsbee

You seem to be the expert on all things gas tank. I know you recommend a specific o ring setup instead of what they sending units come with and a specific sending unit brand, right?

 

[R413]

Yes the return line goes to the pinched off line on the sender. Only the guy that did that can tell you why is closed off.

The 2 vent lines out the LF of the tank, one goes into trunk. The other is "J" shaped and goes straight up and mounts to the shock crossmember with a push in clip. Approx 5" long. So that piece is missing or it would be hanging down and lined up with the tank fittings.

 

[DynaBro]

Yes the return line goes to the pinched off line on the sender. Only the guy that did that can tell you why is closed off.

The 2 vent lines out the LF of the tank, one goes into trunk. The other is "J" shaped and goes straight up and mounts to the shock crossmember with a push in clip. Approx 5" long. So that piece is missing or it would be hanging down and lined up with the tank fittings.

Not missing, it's part of the vent line through the tank now.

 

[4mulas]

Now this is interesting. So the return line is going to the wrong spot. I think they smashed the nipple on the sending unit cap to close it off though. I will get a photo. I worried this might be the case.

Right, and if you followed the schematic in the service manual and thoroughly check out your car before even posting you’d likely find this and more problems.

You can’t see where the vent line in the trunk terminates as it goes back down through the floor and inside a frame rail, so if fuel ever gets in there and needs to drain it drains in the frame rail and runs down the frame and exits onto the ground at the rear of the car.

If the vent lines are reversed in the tank it can also create havoc and the issues you are having, but you remarked that the tank is full and you essentially weren’t going to be able to look. If it were me I’d drain the tank and have a look.

Good luck to you.

 

[4mulas]

Not missing, it's part of the vent line through the tank now.

You cant return fuel into your vent line in the tank. You are pressurizing your system. It’s literally being pumped straight from your fuel pump into the tank. Based on your picture of that weird non conforming fuel filter you have there.

You argue about vented vs non vented caps. Your car requires a non-vented cap period. Otherwise fuel leaks out the filler neck and cap under accelerator.

Make your car just like pictured in the service manual.

 

[DynaBro]

The return nipple in the sending unit just dumps it back into the tank as well. There’s no mechanism inside. Just a short tube. Exact same thing.

 

[R413]

Not missing, it's part of the vent line through the tank now.

Read carfelluy before arguing.

Now you asked what was wrong with your fuel system and we are trying to tell you have the factory did it.

2 vent connections. One for the tube up in the trunk.
Second to the J shaped vent line.

Here is your missing vent line that was installed on these cars when new.

View attachment 1761179

 

[DynaBro]

You misunderstand me. That piece is still present but has been grafted into the rerun line. The fastener portion also still exists but is grafted into the vent going to the tank. It’s all present, just wrong.

Now as to why they ran the return there instead of the sender and did this I have no clue. But I don’t understand how it can be functionally different in regards to pressurizing the tank. Dumping gas back in is dumping gas back in. Neither option has any sort of limiting valve. If I’m wrong that’s fine I would prefer to set this car factory correct but for now I am just going to be certain it matters before buying and going through the massive hassle of installing a new sending unit. And there are questions to unravel its history. Lots of them.

My theory is that small vent you’re discussing does more than we think and indeed needs to be free. The trunk one is not sufficient for breath ability. This is probably why a vented cap MIGHT suffice in the meantime.

 

[dadsbee]

Still not the reason the rubber hoses are wet. Either the clamps didn't seal the hose to the spigots, or as previously mentioned the spigots have pin holes in them..

 

[DynaBro]

Still not the reason the rubber hoses are wet. Either the clamps didn't seal the hose to the spigots, or as previously mentioned the spigots have pin holes in them..

Except I loosened the cap last night and it stopped leaking.

 

[R/T Boy 67]

The tank was designed with two vents from the factory. Plumbing it the way yours is ,is removing one of them. The fuel return line will not pressurize the tank no matter where it is located.

 

[DynaBro]

The tank was designed with two vents from the factory. Plumbing it the way yours is ,is removing one of them. The fuel return line will not pressurize the tank no matter where it is located.

Exactly. Which brings this all back around to maybe a vented cap working in the mean time while I get my resources together to replace the sending unit and run the lines correctly. But it’s still surprising this could cause seepage from both the vent lines, the worst one still being a vent line and the other a feed line from the return hose. I am highly doubtful of the pinhole theory.

 

[EngineerDoug]

Hope this helps - I had a similar problem with my stock '68 tank. This tank has two vent lines, which are routed per the factory setup. I found that the car would stink up my garage after filling up, especially on a hot day. One particularly hot day I noticed fuel puddling under the rear crossmember (one of the lines dumps inside this crossmember.

After some headscratching I realized that one or both of the vent lines was submerged in fuel, and enough pressure developed in the tank to push fuel into the vent line and then into the crossmember.

The solution was to install a vented gas cap (Gates 31670). Note a bonus - this is a locking as well as a vented cap. Fits perfectly and seals better than the old non-vented cap.

This virtually eliminated fuel stink after a fillup on a hot day.

 

[DynaBro]

Hope this helps - I had a similar problem with my stock '68 tank. This tank has two vent lines, which are routed per the factory setup. I found that the car would stink up my garage after filling up, especially on a hot day. One particularly hot day I noticed fuel puddling under the rear crossmember (one of the lines dumps inside this crossmember.

After some headscratching I realized that one or both of the vent lines was submerged in fuel, and enough pressure developed in the tank to push fuel into the vent line and then into the crossmember.

The solution was to install a vented gas cap (Gates 31670). Note a bonus - this is a locking as well as a vented cap. Fits perfectly and seals better than the old non-vented cap.

This virtually eliminated fuel stink after a fillup on a hot day.

I think I read about this on your original post or maybe a reply on a different thread. More than a few guys decided to just not top off and ignore the underlying issue. Which is fine honestly! If they solved it good enough! But I’m buying that cap now for sure. Thanks.