Fuel pushing out filler tube

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rod7515

rod7515

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I have a 66 Dart. Factory tank but it has been modified for a sump kit welded in. The fuel lines have been increased in size to 1/2” going from the pump just below the tank up to the fuel regulator mounted on the passenger inner fender near the alternator. From there the fuel one runs to carb inlet. The return line goes from the regulator back to the tank and it is also 1/2” line.
So twice now I have filled up the fuel tank, drove 5 miles or less and shut car off inside garage. Outside temps both days were around 80*. After the car sits for approximately 3-5 minutes gas starts pushing out behind the gas cap. Neither time was there pressure built up behind the cap when I removed it.
There is a vent in the system in the fuel neck. Any ideas why this is happening? Do I need to install another vent on the top of tank? What’s your thoughts?
Thanks Rod
 
Gas is cold in the ground tank at the gas station and warms up in the car gas tank it expands and over flows.

Had the same problem with a 56 ford PU. If I filled the tank then parked in my works parking lot, when I came out at the end of the day there would be fuel all over the ground, AND in the cab, (hardened rubber filler seal on the in cab gas tank)

I always expected to blow up when I cranked it over to drive home.
 
rod7515 said:
I have a 66 Dart. Factory tank but it has been modified for a sump kit welded in. The fuel lines have been increased in size to 1/2” going from the pump just below the tank up to the fuel regulator mounted on the passenger inner fender near the alternator. From there the fuel one runs to carb inlet. The return line goes from the regulator back to the tank and it is also 1/2” line.
So twice now I have filled up the fuel tank, drove 5 miles or less and shut car off inside garage. Outside temps both days were around 80*. After the car sits for approximately 3-5 minutes gas starts pushing out behind the gas cap. Neither time was there pressure built up behind the cap when I removed it.
There is a vent in the system in the fuel neck. Any ideas why this is happening? Do I need to install another vent on the top of tank? What’s your thoughts?
Thanks Rod
Click to expand...

Do u have a vented cap ? I f its not , u have no vent .
I had a new 68 barracuda that did that , bone stock, its air trapped in the tank.
On my currant 68 fastback , I have an extra vent looping up in the trunk, making a complete coil , up high, and then back down thru the floor and ends about frame level , hasnt puked yet , been that way for about 10 yrs now------------
 
IMHO if the vents were blocked the engine would create a vacuum in the tank and ultimately die.

I don't see how a blocked vent could cause fuel to fill up the fuel inlet tube.
 
I do have the stock filler tube vent piping. However I did increase the size to a 3/8 aluminum tube instead of the factory 1/4" size. But that vent is on the upper side of the fill pipe. Ss for the cap I purchased a cap that one of the members here make from billet material and it's not vented but with a vent in the neck it should not build pressure. With fuel returning to tank I'm sure there is pressure build up. How do I get rid of this pressure?
Thanks Rod
 
The only fuel going back to the tank first came from the tank, basically a loop. No pressure build up even if the tank had no vents. you are consuming some of the fuel in the carb/efi so you have a net loss. This could create a vacuum in the tank if there were no vents

Example...

(Just numbers, not real world values)
You have 5 gph being pumped out of the tank, 1gph is used by the EFI / carb, the return returns 4gph back to the tank. With no venting the tank will develope a vacuum and either crush the tank or stop moving fuel. With a vent the pressure in the tank will be atmospheric or very close to it but it will never be pressurized.

Even with the pump running and the engine not running you are still pushing 5gph out and returning 5gph, no vent, tank has no pressure or vacuum in it, with a vent tank has no pressure or vacuum in it.
 
I can think of one situation, this deal is troubling.

"Let's say" the filler tube is for some reason extended further than "would expect" into the tank. This produces a dome so to say in the tank, because any fuel/ air / vapor above the entrance of the filler tube becomes a "pressure dome." Perhaps this is happening, and warming of the fuel both from temp and from "action" (energy imparted by the pump) causes that fuel to want to expand. It's only point of release is to expand up into the filler tube.

What SHOULD be happening is that if this is the case, the fuel backing up into the filler should be spilling out the vent tube.

The fuel cap should NOT be vented
 
rod7515 said:
I do have the stock filler tube vent piping. However I did increase the size to a 3/8 aluminum tube instead of the factory 1/4" size. But that vent is on the upper side of the fill pipe. Ss for the cap I purchased a cap that one of the members here make from billet material and it's not vented but with a vent in the neck it should not build pressure. With fuel returning to tank I'm sure there is pressure build up. How do I get rid of this pressure?
Thanks Rod
Click to expand...

FAEL EXPANDS W/ HEAT , NEEDS A VENT !! NUFF SAID !
 
So you dont think fuel moving out of the tank and returning would create pressure from the fumes alone?? Do you think its just the temps that allow for expansion. One problem that relates to this would be the fuel fills right up to the filler area before it kicks off as full.
Saturday (or anytime I put fuel in it) when I filled it up the nozzle wont shut off before it's right to the top of neck. I even turn the nozzle upside down and very slowly fill. This way is does not splash out while filling. But once its full it always spits gas back at you.
As for put a vent in it I can do that but wouldnt or shouldnt it vent thru the vent already in the filler neck? Where do you suggest a 2nd vent in the tank should go?
The filler tube is the stock filler and no locating has changed with the tank or neck.
I remember as a kid these were always hard to get gas into without them kicking back at you. Believe me I've had plenty of gas baths from the older cars as my dad had a gas station and I was fortunate to have to pump gas everyday for over 10 yrs of my early life!
Thanks for everyone's help and ideas
Rod
 
VERY first thing I'd do is make sure the vent is actually open, and make sure the cap is actually sealing. I'm sure the activity of the pump is going to raise vapor pressure of the fuel, but a properly open vent should just simply let it out. Should not be an issue.
 
Based on everything you had posted I am 100% convinced that the tank is just getting over full, and a change in temp, is causing the fuel to expand.
 
fill it up and connect a pressure gauge to the vent
 
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