Gas leaking from tank after filling up...

[stuka1166]

Filled the tank on my Road Runner...Noticed gas leaking from under the car...Released gas cap and it "de-pressurized"...Leaking stopped.

No clue what's going on, other then building pressure...BTW, the car is very hard to start as well after refueling.

Any clues ??

Thanks !!!

 

[skrcsmith4]

Could be leaking from the sending unit. My 69 rr leaks if I fill the tank. Friend has a 69 super bee same thing. Also I had a 69 in in 1975 same thing leaked if I filled the tank

 

[Cranky]

Are you hot filling it to the very top? Had a road cruiser 70 Challenger that would leak when filled up when hot but it would push it out of the cap even before I could get it back on. Gas expands and a hot day with a car that's also hot will usually make it happen so I got to where I would pull the nozzle out on the first click off instead of trying to get it topped off. That did the trick for me.

 

[Dreamcatcher]

You might also look at the rubber donut where the filler neck goes into the tank. Mine leaked there. There available for about 20.00. As far as hard starting and pressure in the tank there should be a tank vent that may be plugged. Some older cars also used a vented gas cap.

 

[Bb70charger500]

I also had a filler neck grommet leak on me ,I never filled the car up so never noticed it till one day I was driving home had a nice police officer pull me over and told me every time I get on the throttle gas come pouring out the back .
$10 later my gas mileage went from 14 mpg to almost 20mpg

 

[GearAddict]

Could be leaking from the sending unit. My 69 rr leaks if I fill the tank. Friend has a 69 super bee same thing. Also I had a 69 in in 1975 same thing leaked if I filled the tank

I replaced my tank... turned out to be the sending unit seal... usually you will dump a little gas on the road as gas sloshes in the tank under acceleration.

 

[1969CoronetR/T]

I been having the same problem for the last five years. I just fill it half-way for a temporary fix. Last summer I went out to my garage and noticed a small pool of gas on the floor so I took the gas cap off and it shot a good foot out of the tank for a good three seconds. Also, had a few people top beside to tell me that I an leaking gas. After the garage incident I figured if i do not fill it all the way it can expand and not purge as much. Race fuel is over $9.00 a gallon...

 

[Dennis H]

Description soinds like possible vent issue. They are at the forward upper part ipof tank and tubes are visible in trunk. Need more info. Car on incline when parked etc.

 

[The Horvaths]

I never top off when it is warmer outside than the underground fuel storage tanks (about 50 F). Fuel expands a good bit when heated.
Also, all of my classic vehicles have vented gas caps.

 

[bigmanjbmopar]

I had a similar issue was real bad if park slightly downward with a full tank would vent out like a 1/2 gallon! Made sure vent lines were good per the FSM also when that didn't fix it I took my no vented cap and drilled two 1/8" holes in it stopping just inside before the gasket. now all I get is a slight smell with a full tank fill up on a hot day but no more on the ground! I also tried putting a fuel filter in reverse on the short vent line and took it up higher to the body, that didn't work.

Here is the inside of my tank and the FSM for 69 vent lines for example. The idea was one line went to the back of the tank so when you were downhill it could vent and one was short at the front of the tank so when you were up hill it could vent. but today's gas expands fast and evaporates fast and I think overwhelms the old vent design, I could not find a vented cap to fit my fuel neck so I drill the holes and everything works great and there was no cost to me

 

[moparedtn]

Yeah, I've got a repro tank and repro sending unit and I've had the thing out twice now, trying to get a good seal on the sending unit gasket. I put over half a tank of gas in it and here come the drips.
Even permatexed her up last time and used a thicker gasket.
About ready to weld the damn thing (or maybe JB Weld).
Just bought a new cap also and it's not vented. Figured that was ok, since the vents that go up in the trunk are there?

 

[1969CoronetR/T]

I noticed after parking my R/T outside my warehouse a few miles from where I filled it up that it was leaking. I looked under the car and it seemed to come from the front of the gas tank and not the inlet tube. So, in my case it is the vent tubes or or the sending unit. I noticed that there was a pressure release when I took off my non-vented gas cap so maybe the pressure blows it out the vents tubes. I normally only put five gallons in at a time and this time was no different and it still purged.

 

[Dennis H]

I fill mine. Make sure that the vent tubes visible in the trunk are routed high enough at the u -turn bend.

 

[Icecobra]

I have the problem of leaking after fill up. I looked in to the fuel separator and I am installing this on the vent tube. It separates the fuel from the vapor and is about a 8 ounce catch tank. It lets the vapor out and holds a small amount of fuel in it that drains back in to the tank. I am hoping this works as fuel dripping from under my car really bugs me not to mention the fear factor and fire possibilities that can occur. I have not installed this yet but hope to in the next weekend or two...

 

[stuka1166]

I had a similar issue was real bad if park slightly downward with a full tank would vent out like a 1/2 gallon! Made sure vent lines were good per the FSM also when that didn't fix it I took my no vented cap and drilled two 1/8" holes in it stopping just inside before the gasket. now all I get is a slight smell with a full tank fill up on a hot day but no more on the ground! I also tried putting a fuel filter in reverse on the short vent line and took it up higher to the body, that didn't work.

Here is the inside of my tank and the FSM for 69 vent lines for example. The idea was one line went to the back of the tank so when you were downhill it could vent and one was short at the front of the tank so when you were up hill it could vent. but today's gas expands fast and evaporates fast and I think overwhelms the old vent design, I could not find a vented cap to fit my fuel neck so I drill the holes and everything works great and there was no cost to me

The bottom drawing...The gas leaks from the shorter vent tube...Sitting on level ground

 

[Dennis H]

The bottom drawing...The gas leaks from the shorter vent tube...Sitting on level ground

that's right, mine too. When the tube height was rased it stopped.

 

[clazar]

I also had a similar problem. My car has California emissions on it. They have different gas tanks. 4 metal vent tubes come out from the pass side of it & go up into a tube in the trunk. One of the rubber lines attached to it was leaking. The gas ran down to the front of the tank & dripped. Only replacement of the line was necessary. If you have a Calif tank, you can tell by looking in the trunk & you'll have a metal tube attached to the pass side trunk floor.

Chuck