Got a fuel tank vent leaking issue.

So while the road runner is on the lift i have been trying to figure out why the fuel tank has started leaking out of the vent tubes. The tank was replaced two years ago with a Spectra unit. It has been working perfectly but just recently when i fill it up for some reason it will spit fuel out of the vent tube like crazy.

I see that one tube goes into the frame and i think then into the trunk?

The other just goes up and has a curved end by the body.

Any thoughts on why it would start leaking out of the curved end vent tube? It has has never done this before??

Here's a couple of photos of the tubes.

Thanks for any ideas.
Stu

There was a time where 69 Roadrunner tanks had the vent lines switched inside the tanks on the repops. Switch the rubber hoses and see if it fixes it.

Ok that's worth a try. I just dont understand why it was fine for two years and just now started leaking. I wonder if the line in the tank may have broken somehow and is sucking up fuel??

hi mid, yes your "j tube" is connected to the spectra short vent line that is only about 6"to 8" long in the tank. try to switch the rubber lines around to see if it solves the problem. more aftermarket headaches. ronnie

Are you filling it & 'topping it off' when the outside temp is warm?

Fuel in underground tanks is cooler than it will become in a smaller gas tank above ground on a warm day & fuel expands as it warms up.

I try to fill up 10 miles or so from home (with no topping off at all, ever) if I know the car will be sitting for more than a few hours.

Thank you guys for the good idea!


I will try that for sure. Since this started happening something must have either come loose or broken in the tank.

Are those Runner hoses designed for fuel? Do you fill up where the fuel has E85? May be the rubber is breaking down and slipping past where it's clamped. Looks to be the case on one of your lines. The culprit looks to be the outside hose since there's a fuel stain next to the clamp. With the fuel expanding I'll bet when you have a full tank the fuel shoots out of the path of least resistance.

Not much could go wrong unless something got damaged in some way. I would look at pretty much the only thing that would go bad such as the rubber lines. I would replace them all and make sure the steel lines are clear.

My buddy was going to use his new Snap-On bore scope to look into the tank and see what may be going on, but it broke three days after he bought it. Go figure....

The way that is dripping on the edge and blowing forward on the shock, I would get a mirror and check out the sending unit seal if you haven't. The ethanol will blow them up also, or the seal could just be bad or not seated well.

If you sold the car, and the leak just started with the new owner, I'm betting he is adding fuel after it shuts off (rounding up to the next even $$ amount on the pump), then parking the car in the sun. The tank is getting over filled.

I live a block from the gas station I use here. I have learned not to fill the car then drive it home and park it. I fill up before I'm leaving to go somewhere, and then hang up the pump when it shuts off. I'll pay whatever the odd change the pump may shut off at. Gene

We have it up on the lift and it was leaking from the one vent that had the curved type metal tube end. No where else. So i will try switching the two and see what happens.

Stu

Since it has been toasty throughout the state recently, you probably are experiencing lots of vaporization from the alcohol laden fuel and the stock venting has issues with keeping up. This will cause the tank to get pressurized and allow the leaks. You may want to revise your venting and improve it.

Interesting idea!!!

The fuel issue, like yours, has been an ongoing discussion on the FBBO site. One guy tested the current pump swill and found that the fuel boils at 150*. Think about that. Your engine is running, on the coolant, at 180* or more. Mix in the radiated exhaust heat plus other heat sources. On my own 65 Coronet, after driving it for 20 minutes or more, would have the fuel boiling in the tank. Car has 3" TTI exhaust that at that area has anywhere from 1" to a little more for clearance between the pipes and the tank. The car would be fun to drive since it was blubbering from fuel boiling in the carb too. I put on a carb heat shield plus used the blocked off heat riser intake pan shield/gasket and that helped on the engine side but the other end was still an issue. For sure we need better venting back there. Is your fill cap vented or non vented? Mine was vented but I still got a whoosh when it got opened.

I have a vented cap and well. I checked it over to make sure nothing to make it looked fine. This issue just started recently and even happened ( to a much lesser extent) at my buddies shop when the car was sitting and the engine cold.

When it happened to me at a car show last month it dripped out steadily from both side of the tank like it had a hole in the tank for a solid hour. I thought the seam had gone bad but that not the care as on the life you can see it coming out of the smaller curved vent tube.

Maybe check the vent line and make sure there are no restrictions. On the "Tanks Inc" site, they say not to use the commonly done curly cue vent that some people make as it can collect liquid in the low spots, from the fuel condensing after cooling off, causing a restriction in the venting. My neighbor had a tank made out of aluminum, bad choice btw, with the vent done that way. He has fun filling it sometimes because that vent is restricted. I need to make a straight one for him down the road.

My bet is the fuel vapors are pushing past the hose clamp and that the hose needs to be replaced. Also, since you were see fuel on both sides I'll bet the fuel is running down the seam and dropping on the other side of the car.

That is so true. This pump gas we get today is junk. I had some issue when mine started to boil in the carb. This was back a few years when the gas started to get worse. At first I thought my needle and seats were bad as it was boiling the fuel out the carb internal vents into the eng and loading up. I put a 1" phenolic spacer on it and a heat shield and moved the fuel line away from the eng heat as much as I could and it took care of it. Makes sense if the fuel gets hot enough in the tank as I have not had that problem but I do know they change to winter blend here in Md where I live and then back to summer around April as I got gas in March last year and when sitting in traffic for a long while on a 70 degree day I switched my electric pusher fan on in front of the rad when the eng was at 185 and to my surprise the fuel started to boil in the carb as soon as the pusher fan pushed more rad heat over the eng. And the eng never went over 185 I just turned on my electric fan because it looked like I would be there a while. It would never do that on summer fuel as I sat for a 1/2 hr in the summer with my electric fan running and the car never went over 185 and I had no problem at all. This pump gas is junk. Ron