What foam to use in gas tank vent lines?

Drove the car to work yesterday parked on an incline that had the rear higher than the front. I smelled gas and a small bit of fuel on the ground. I chalked it up to the incline and a 4/5ths full tank. After all I have good vent hoses and the plastic filter holder plugged in the end of them, and its all securely held up in there by the body clip above the axle. Well today i parked level and only burned a little more gas but sure enough the little puddle came back. Looking at the 70 manual 80-3 shows not the plastic filter holder but maybe 3 to 4 inch foam strips are to be stuffed in the vent lines. I want to get the right foam for breathability but need some that wont melt because of the gas. Some suggested lawnmower foam does anyone have good success with this or anything else?

 

Yes but that depiction is in the Chassis Manual. I submit this was superseded by the 70 Factory Assembly Manual at 8-6.1. The Assembly Manual shows a surge tube with a short foam insert at the top. I would not stuff foam in the lines.

 

A surge tube is what Larry's link calls a vent tube. I would start out with no foam in the surge tube set up with the lines clamped vertically per factory specs and check the results.

 

That is what I used on my car when I put in a new gas tank. No problem so far with a full tank on a hot day.

You should also make sure your cap is vented. 70 is vented and 71-up is not.

 

Funny enough I do have the plastic surge tube end in my current tubes (which are vertical and up in the body clip). There was no filter with it when I got it though. Someone irl had said just stuff a little cotton in it and it'll be fine. But recent problem and the manual are convincing me otherwise. On the matter of the gas cap the manual did say on 80-2 in the top middle paragraphs that "(A "NO VENT" type filler cap is used)" so thats what I am using. My car is an AC car and has a return line but I was assuming that the corner vent would be enough and the manual would have stated otherwise. With the mention of possible revision changes and the fact the car is older than me so I lack the "know what was normal because I lived through it" knowledge. I am doubting a little lol

 

If your car is a 70...it's a not vented cap. If it's a California emissions car, I think it's vented.

 

You probably have a leak someware on the seam of your tank. It just takes the right amount of gas to make it leak. keep driving and looking for puddles , but that will take time if you want answers NOW then you need to dive underthere and get eyeballs on it. You could always loop your fuel lines and add some compressed air to it. Youl see it or hear it for sure. Im sure your smart enough to not over do it. Ive done it to get a good siphon going on a car not mine You can see the tank expand a little, nothing to worry about.

 

If you want foam use a foam lawnmower filter and cut it to fit your needs.
But.
If your car didn't do this before, and nothing has changed except possibly the foam, then I would suspect another problem.
Because the foam does not stop fuel from moving it only slows it down, really it is there to keep the air moving slowly. The vent tube being where it should be should keep the gas in the tank, as the tube should terminate higher than the top of the tank. And another thing, if you see gas on the ground, concrete, blacktop it must be leaking over time because in the summer heat it should dry just about as fast as it hits the ground. Rule of thumb, if the tank is vented to the atmosphere use non-vented cap. If, like some station wagons it is not vented to the atmosphere, use a vented cap.
On one of my cars I had a fuel smell when I put more than a half tank in it. Couldn't find it, tried several times. After a long while I finally saw dirt gathered on the line that comes through the pick-up. It was seeping a little and drying before it dripped, all I had was the smell. It is a 66 so the pick-up comes out the front, so I removed it and had my local radiator guy fix it, no more smell.

Good luck,
Mike

 

It may not supposed to have a vented cap in 1970 but putting a vented cap on it kept mine from spewing fuel. If you park it at an angle, the fuel can be pressurized by the air trapped in the tank with only one vent and it will force it out the only available opening it has. Popped the old non-vented gas cap and it quit spewing fuel out the vent. Swapped for a non-vented and hasn't had it happen since. Your mileage may vary but it fixed my issue. Been there, lived that.

 

Pretty solid advise guys, I will concentrate on that area to find the leak but I will be looking at the hose conditions again, how well they are sealing against the nipples and see if there are any deceptive trickles from the seams throwing my area of attention off by backing the car up on some ramps. If I still have some trouble Ill buy a vent cap cause hey they're cheap anyways and use it for a bit and watch the results to help pin the problem down. Thanks guys!

 

My Riviera has a vent rubber line to a tube that loops into my trunk and then plugs back into the tank . Dosent seem like a vent though.

 

If you guys are talkin bout the (red square foam seal) I used 2 part epoxy. Foam sealant the stuff they use on frame rails and sheet metal to bond panels together. After a car is wrecked and gets repaired . Fuse and Vavoline make it SEM and 3M

 

Check the condition of the short rubber lines from the end of the metal lines to the tank.