Gas tank pressure

[Carmine]

Hi everyone. Beautiful day here in the northeast. Sunny and 64 degrees. Might be the last one like this, so I decided to go for a ride. Was out about an hour or so and the car ran good. Smooth. Returned home and thought this might be my last ride of the season, so I decided to put some Lucas fuel stabilizer in the tank. Have about 1/4 tank left. I undid the gas cap which was accompanied by some back pressure. I mean serious back pressure. I've heard and felt this before on other cars, but this was the most ever. The cap is brand new for my '62 which has no return line. Is this amount of pressure normal?? I don't see how it can be. Is it recommended that I drill a hole in this cap to relieve the pressure. Thanks, Carmine.

 

[La Hot Rods]

That is a common problem with new gas caps
I don't think they can sell one that vents to the outside anymore.
One way to look at it. You may may not have a vapor lock problem if the system stays pressurized.

 

[bobs409]

Yeah, ever since I put a new cap on my Jeep I get that pressure build up.

 

[Carmine]

That is a common problem with new gas caps
I don't think they can sell one that vents to the outside anymore.
One way to look at it. You may may not have a vapor lock problem if the system stays pressurized.

Ok, but is this amount of pressure a problem?? The car has been running well. I'm not too concerned about vapor lock. I'm somewhat inclined to drill a discreet hole in the cap to relieve the pressure. I don't know how this could hurt anything, but I don't need more problems if this isn't the thing to do. It just doesn't seem correct, this amount of pressure, Carmine.

 

[jdk971]

i want to know the answer also. i have a in tank fuel pump for a ls engine. and a new vette regulator at the tank and no return line.
also a vented cap. jim

 

[blkblk63ss]

If you drill a hole you will get gas smell in garage,and your gas will evaporate out of your fuel tank.If you have a modern car it pulls pressure automatically from tank. I would not worry about your older car''s . My 63 is that way ,and will leave it that way.

 

[La Hot Rods]

Just open it up when you get out of the car every now and then and before you park it in the garage

 

[Carmine]

If you drill a hole you will get gas smell in garage,and your gas will evaporate out of your fuel tank.If you have a modern car it pulls pressure automatically from tank. I would not worry about your older car''s . My 63 is that way ,and will leave it that way.

The pressure doesn't seem to affect its performance. I was just concerned about the pressure affect on the tanks seam or the rubber hose/fittings connecting the filler tube to the tank. If this pressure was just a little pssssssssssssstttttttttttttttt, I wouldn't be concerned over it. But, it was a lot. The most I've ever experienced from any car. I never realized a condition like this could exist until I was replacing my sending unit and took off the rubber line attached to it. I knew the gas in the tank was below sender but it shot out like it was a nozzle at a gas pump. Much force behind it. I thank everyone for their responses but I'm really not sure what to do about this. I'm not very comfortable with the way it is. Guess I'll look at some other caps to see what is offered, Carmine.

 

[bobs409]

Maybe a good used cap or NOS? Lots of GM cars would have used this style.

On my Jeep it gets worse as the gas tank gets emptier, not even a problem when it's full. I usually let the pressure out when returning home.

 

[bobs409]

If you drill a hole you will get gas smell in garage,and your gas will evaporate out of your fuel tank.If you have a modern car it pulls pressure automatically from tank. I would not worry about your older car''s . My 63 is that way ,and will leave it that way.

I don't see how it would be any different than an original cap that vents the pressure out. There would be no pressure build up so little fumes pushing out. I have 3 cars in my garage with original caps on and never a gas smell.

 

[DonSSDD]

Might find a well made cap from a Corvette supplier for say a 63 Corvette? The correct one should have a one way vent to allow air in as the tank empties.

 

[Carmine]

Looked at a couple of vendors and they sell vented caps for '58-'63 Chevys. The closeup of the caps shows the word "vented" embossed on it. I just checked my new cap and don't see the word vented anyplace on it. Ordered a new "vented" cap and some valve cover decals. Hope this puts my mind at ease. Have all winter to think about it. It snowed here yesterday. End of the season for me, Carmine.

 

[bobs409]

Yesterday it was 70, today it's 40 and and snow showers! Crazy weather...

 

[blkblk63ss]

Looked at a couple of vendors and they sell vented caps for '58-'63 Chevys. The closeup of the caps shows the word "vented" embossed on it. I just checked my new cap and don't see the word vented anyplace on it. Ordered a new "vented" cap and some valve cover decals. Hope this puts my mind at ease. Have all winter to think about it. It snowed here yesterday. End of the season for me, Carmine.

The cap will be vented to the inside. It will draw in but not out.That is the way mine is. You are trying to reinvent the wheel Carmine!!!!!

 

[63impalass409]

Is this suction pressure? Can't that collapse a fuel tank?

 

[blkblk63ss]

I don't see how it would be any different than an original cap that vents the pressure out. There would be no pressure build up so little fumes pushing out. I have 3 cars in my garage with original caps on and never a gas smell.

Have you ever checked to see which way the vent go's. It can be vented to allow air in but not out . It is a one way vent.

 

[blkblk63ss]

Is this suction pressure? Can't that collapse a fuel tank?

no.

 

[blkblk63ss]

As a side note Carmine, newer car's have eliminated this problem by drawing vapor's from fuel tank's as they drive. That is why if you do not have a gas cap on properly ,it will set a check engine light to come on because it cannot properly pull a vacuum from tank as it has a vacuum leak.Engineer's have fixed this problem year's ago.The old car's are just that way. Oh and if you set a open container out in the open with gas in it ,say a cup or so ,see how long it take's to evaporate,compared to one that is closed.That is why the cap's allow air in ,but not out.

 

[bobs409]

Is this suction pressure? Can't that collapse a fuel tank?

Not sure if you're asking me or Carmine but my Jeep pushes pressure outward. I press in on cap to angle it and I can feel the air pushing out on my fingers.

 

[bobs409]

Have you ever checked to see which way the vent go's. It can be vented to allow air in but not out . It is a one way vent.

Can't say I have. Never really thought about it before.