Gas pouring out of filler neck

[thebebop]

Ok so this morning I fill up my 55 2nd series. I never top my cars off. When the pump clicks off I stop filling. This afternoon I go our to the shop and there's a strong smell of gas. I notice some gas on the ground next to the truck right under the gas cap. So I open the cap and a whole bunch of gas spits up and out of the filler.

I realize the heat will cause expansion but I've never experienced this on any of my previous vehicles....any suggestions on why this is happening? Or is it normal?

[OrrieG]

I'm guessing someone has replaced the original vented cap with a non vented one??

[mr48chev]

Probably expansion is pushing the gas out. That might be especially true if you filled it at night or when it was cool. Gas expands quite a bit and if the truck is parked at the curb on the street or on a slight incline to the gas filler side that increases the chances of it running over.

If you had a non vented cap on the stock tank you most likely would have had the engine die after a few miles and then hear a big woosh of air running into the tank to fill the vacuum the pump created in the tank. I've had them suck the sides of the tank in on my 51 Mercury with the stock tank when I first got it together in the late 70's.

A non vented cap would probably push gas through the needle and seat with the pressure build up in the tank before the cap leaked.

I'd just make sure I didn't park with the filler side of the truck lower than the other side when the tank was full and see if that took care of it.

[thebebop]

Thanks for the replies...here is a picture of mine...I thought it was a vented type. I did fill the truck up when it was about 85 degrees out and then drove it for about 20 minutes. I parked in the shop where it was probably 95 to 100 at the time it overflowed. It was filled up in a level area and parked the same.

[mr48chev]

If you have a stock tank and have driven the truck at least 20 miles ( and probably more like ten miles) at one shot with no problems that is a vented cap. My 51 Merc would die after about five miles with a mismarked cap. It did it three times at the same spot on the way to work with two different caps out of the same batch at the parts house.

[tmoble]

that's technically a vented cap but it only lets air in, not out. I think there's guys on here that fixed them with a small drill bit.

[mr48chev]

True in theory it only. lets air in to take up the space that the gas left after it was pumped out by the fuel pump but some may vent to the outside when pressure builds up in the tank and not all of them or the necks seal that well after that many years.

[Coupeguy2001]

I make a gas cap baffle that fits under the cap to prevent the gas from dripping off of the gas cap if you fill the tank.
Asking $10 for the baffle, and $5 to ship.
works great for tank fill-ups down to 3/4 full, where you won't get the problem.
they have anti-rattle plastic shims and don't rust or corrode since the washers are silver plated.
I have about a hundred of them.