Hi, I have a huge issue with my 1970 el camino. I filled the gas tank two weeks ago, drove the truck only a few miles (approximately 10 miles) then put the truck away under a canopy for the last two weeks. [More... the weather in El Paso, TX is getting into the high 90's ..this is for reference information only.]

I walked by the truck and smelled gasoline tonite. I thought geez I have a leaking fuel line but NO. The gasoline was dripping out of the inlet pipe or inlet tube right at the gas cap (ay know, where you put the gas in the tank). The gas cap is a non-venting cap. I slowing removed the gas cap and gasoline burst out of the inlet tube...and I would have to guess it was over a gallon of gas SPRAYED at high pressure out of the inlet tube. It looked like water blowing out of an elephants trunk! After the spray slowed down a lot...I slipped a oil drain pan under the inlet tube an caught at least another gallon of gasoline spilling out.

I have read a few other threads on pressure in the tank but none seems to answer my question OR maybe I just don't understand them enough. They look about vented gas caps and talk about vent lines.

I don't know what vents line this El Camino has. And tonite as I am writing this the ground is saturated with gasoline and has been sprayed down with water ....so I am not getting under the truck to look in the dark for vent lines.

Please add your clear and complete comment for me to understand and learn from the Guys who are the Experts.

Thank a lot.

I have a 70 Elky, mild 350.
Most of the time when I go to fill up, I get pressure...that's about all. A little Whhhhosh, the cap jumps into my hand.

Retired Army. The big trucks had a "fill to here" line to leave room for the fuel to expand. Bradleys and Humvees you filled to the bottom of the screen. Tanks, well, you just kept adding fuel!

Though you got way more of a mess than I ever heard of.....I just think your fuel expanded. Did you fill her up on a cool night or morning?

I would look at the vent line first. It must be blocked or crimped.

Aren't El Camino's supposed to use a vented gas cap?

Dan

You mentioned that you have a non-venting cap so I assume that you have EEC and 67shovel's advice to check the vent lines would seem to be the first place to look. A vented cap is not the solution since the cap is designed to let air IN to the tank not out.

My '70 Elky (without EEC) suffers from pressure buildup as well, although not to the same extent as you experience with a fountain of gas shooting out. However, the pressure buildup is enough to cause concern. It all started when I replaced my tank this past winter due to a pinhole leak on the top of the original tank. Prior to that, I had no issue and can only assume that if the same problem existed with the original tank, perhaps the pinhole vented pressure buildup. I searched all of the prior threads that I could find, only to discover that there are lots of guys who have this pressure buildup problem also but not a single concrete solution was ever given - just a lot of speculative answers.

My "fix" if you want to call it that has been to take a vented cap and rig the vent valve so that it is open all of the time, allowing air in as well as pressure out. It's not the ideal solution but at least it prevents the buildup of excessive pressure that could open a seam in the tank or force gas out of the carb. On the down side, there now is a noticeable gas smell from sloshing when making a turn or accelerating. The ideal fix would be a two-way vented cap but such an animal doesn't exist. I'll be watching your thread replies closely in the hope that somebody out there has a singularly brilliant idea on how to solve the pressure problem - not just more speculation. Good luck and let me know how you make out.

I also have the gas tank vent problem. And being in the same part of the country as Ryan, (albuquerque), I'm also in need of a fix. My 69 Elky has a later model gas tank in it. A 69 gas cap would not fit the filler neck. A '72 cap fits but is not vented. So I drive with the cap turned just short of, well, on. I mean it's kinda dangling really. So my fix is gonna be an EEC vent setup. So were does the vent "canister" go? I know the charcoal can goes on the drivers side inner fender well. But the vent can, (the oval shaped thing) has got to go under the car in front of the gas tank above the rear axle? Ideas..........
Hey Ryan, my elky used to be a southern New Mexico car, I wonder if some of our parts got mixed up at a body shop down there at some time ?? LOL.

The best solution, really, is to simply not fill the tank up completely in hot weather. The fuel will be relatively cool sitting in the undergound tanks at the gas station. If you don't drive at least a couple gallons out of the tank right away, that fuel will expand beyond the capacity of the tank and has few places to go outside of the vent tube (earlier cars) or the filler neck.

Back in the days of Trans-Am racing, Roger Penske use the trick of packing dry ice around the gasoline storage tank used to fill the tank on the cars while they were in the pits. By his pit crew manager's estimate, this allowed them to pack 24 gallons of fuel in a 20 gallon tank during the pitstop! Of course while racing the fuel was being consumed quicker than it was expanding so they never had an overflow due to expansion issue like a street car may have, but the point is, fuel expands quite a bit between the cool environment in the ground to the warm environment in your car.

Of course like all bright ideas in the world of racing, Penske's idea was deemed illegal and banned.

Good Afternoon, I looked for the vent hose on the gas tank....I only see one hose coming out of the middle top of the tank. So, I don't see any vents!!!
I am not going to remove the tank today to see what is on TOP of the tank...But don't think that will show any new clues, or vents.

Someone asked what the weather was the day I filled the tank. It was May 26, high 86 at 2:42 PM per National Weather Service Report. I actually filled it up at noon, but did drive the truck in the afternoon when it was around the 86 degree mark before put it back behind the fence and under the canopy.

This seems like a common issue. I took out about 6 gallons of gas today because I thought it would help give the remaining gasoline in the tank room to expand. I will NOT fill the tank to the brim next time.

Mr. Classic Gary,
About my El Camino and El Paso, It was bought and sold right here in El Paso at a local dealership. I have the build sheet from under the seat. So, Southern New Mexico parts could be on the truck. haha Your comments made me smile.

if anyone wants to do it, you could drop the tank, pull the sending unit out, and drill a hole in it to put a vent line like a fuel cell has. just run a 3/8" fuel line in a loop to somewhere under the car with a vent on it like you find on axles and transmissions.
i can't guarantee that it won't smell like gas from time to time, but the tank will be effectively vented.