jayfire

I have a 68, but looks as though the fuel tank is a 76. I put 5 gallons in two weeks ago and it's dry. Put in another 5 gallons and after a few minutes, it was pouring out top of the tank somewhere. It has a vented cap, but still has pressure. Let it sit overnight, came out this morning and it was pouring out again. Only stopped when I took off the vented cap. Pressure?? Should I try another cap? Drill a hole in this one and see if it still happens? Any other ideas? Thanks

68/70Vette

A 68 tank has a provision for a fuel return line located on the passenger's side of the tank at the top. I know a 70 tank has a provision for the vapor return hose at the driver's side of the tank. Fuel could not come out of this outlets unless the tank was absolutely full.

Don't know how putting 5 gallons in could could have fuel coming out the top of the tank. I think the 76 tank has a membrane, but I have no experience with these tanks.

You need a vented cap for a 68. If you don't know if you cap is vented or not, simply sit it a little sideways over the fuel inlet, but don't turn or tighten it..it'll be vented.

A nice new factory duplicate tank for your 68 is only a little over $200 from Quanta. Installing the tank is a good builder of character.

0Willcox Corvette

68 cars used two different tanks, one for big block one for small block. The sender in a 1968-1974 tank was on the bottom of the tank, the sender for the 1975-1977 tank was on top.... and indeed had a bladder.

If you install a cap on a car that is designed to be vented, in most cases the fuel pump will collapse the tank and all 68 cars used a vented cap so you want to make sure you have a vented cap. (it will say vented on the cap).

Have you checked the rubber hoses at the tank to make sure they are not leaking?

Willcox

jayfire

I was looking up fuel tanks and mine looks like 75-77 tanks. After putting about 4 gallons of fuel in the tank, put the cap on and fired it up, after about 30 seconds of running, shut it off and fuel is pouring down pass side of tank and around the filler neck. Wasn't until I pulled the cap it stopped leaking. (Only 4 gallons of fuel in it!) I let it sit overnight with the cap on, like normal. Go outside the next morning and fuel is pouring out along the pass side again and its wet around the filler neck again, even though car hasn't been started in more than 12 hours. I pulled the cap off, heard the hissing, then leak stopped. Maybe I have a faulty vented cap? I drilled a hole all the way through and put it back on last night, its going to be a hot one today, so I will see if I get any pressure and start leaking again. Remember, this is all with just 4 gallons of fuel and not running the car. Thanks

0Willcox Corvette

The cap being vented or not should not have any implication on the tank leaking.
A non vented cap on a car requiring a vented cap would cause the fuel pump to collapse the tank... not leak fuel. The fuel pump would create vacuum pressure on the inside of the tank if the tank is a sealed unit.

Where do the sending unit wires attach to the tank sender? You should be able to see them on the bottom of the tank if it's the correct tank.

Regardless of what is going on with the cap or the tank, check the rubber hoses at the tank and at the sender to make sure they are not leaking.

Willcox

mysixtynine

68-69 need A vented cap. The cap does NOT let air into a tank on these cars. The tanks have a vent in the top of the tank (see second picture) by the filler neck to allow air into the tank. The vented cap allows pressure out only. Look a the disassembled cap below (first pciture)... no way air could get pulled past that rubber seal... its a pressure release only. These newer caps don't seem to be made correctly as they seal too hard. I had to remove my rubber seal so that tank could vent... after driving I would hear hissing popped the cap and it almost blew outa my hand there was so much pressure. I removed the rubber and now it vents nice (I don't suggest completely defeating the seal like I did by removing the rubber probably should have taken a few loops outa the purple spring but I am not sure how many times I could un-bend the cap crimps before they let go).

You building up some pressure maybe ok... it sounds like something is compromised on your tank that is allowing the pressure to push the fuel out. If you truly have a 76 tank then you will have other hoses to contend with like the evap. system.

Can you show us where the fuel is leaking from... the return line on this tank is way up high on the passenger side and does not have a line going down into the fuel so even if it was blocked off poorly and leaking due to pressure 4 gallons would never reach the top of the tank. A 76 tank is way different than a 68 69 .



Vent on top of tank to allow air in for displaced fuel being pumped out.

jayfire

The sending unit and all the wiring is at the top of the tank next to the filler neck. That's why I'm assuming it's a 76 tank. Since I drilled a small hole through the cap, haven't had a leak since. It was definitely leaking somewhere from the top, because it was all wet around the filler neck.

mysixtynine

If it is a 76 tank then the return appears to also be in the sending unit itself.

This year would also have an evap. recovery system as well. So I would guess there would be nipple(s) on the tank itself somewhere for those.

This tank would also NOT have vented cap. So if someone put a 76 tank in a 68 and did not provide for the evap and or may have blocked off the return then you had a completely unvented tank for both fumes to escape and displacement air to enter.

The return does not protrude down low enough into the fuel where your reported 4 gallons should be able to be picked up by the return during a pressure situation unless maybe the bladder has some how collapsed and is making the tank less spacious.


There appears to be an additional nipple on the top of the tank towards the drivers side of the tank... my guess is this is the evap connection??

jayfire

Yes, that is my tank. I think I will just pull it and put in the correct tank. Peace of mind! Thanks