Correct Gas Cap? Too much pressure!

[demian5]

Ok so I looked and searched on here and found nothing definitive.

Stant site shows:

1970 and earlier 10491
1971 10582
1972 10572

I have a 1970
I don't have any vents on my tank and I get crazy pressure and the cab stinks of gas. The back side of my cap has a vent system but its plastic and I cant pull it apart to cut the spring.

Help? Suggestions? Knowledge you would like to share?

The old one just leaked down my cab and bed when cornering.

[Bob B.]

Originally Posted by demian5

Ok so I looked and searched on here and found nothing definitive.

Stant site shows:

1970 and earlier 10491
1971 10582
1972 10572

I have a 1970
I don't have any vents on my tank and I get crazy pressure and the cab stinks of gas. The back side of my cap has a vent system but its plastic and I cant pull it apart to cut the spring.

Help? Suggestions? Knowledge you would like to share?

The old one just leaked down my cab and bed when cornering.

Do you have the correct 1970 gas tank? If it does not have the vent line on top you might have a 1969 tank, or one for a 1970 without EEC. If that is the case you might want to try a 1969 cap. A truck with EEC will have the extra vent line on top of the tank and the charcoal canister under the hood.

[FRCvette]

I had this same problem with my 70. I ended up drilling a very small hole in the backside of the cap. No more pressure or smell.

[rechinca]

Originally Posted by FRCvette

I had this same problem with my 70. I ended up drilling a very small hole in the backside of the cap. No more pressure or smell.

FRC is it possible to post a pic of the hole you drilled for reference on the cap?

[demian5]

Originally Posted by FRCvette

I had this same problem with my 70. I ended up drilling a very small hole in the backside of the cap. No more pressure or smell.

Pictures of this or you are telling tall tails...

[FRCvette]

Originally Posted by demian5

pictures of this or you are telling tall tails...

[demian5]

Originally Posted by FRCvette

Attachment 1863796

And it DOES NOT leak all over the side of the truck when cornering right?

[El Dorado Jim]

Originally Posted by FRCvette

I had this same problem with my 70. I ended up drilling a very small hole in the backside of the cap. No more pressure or smell.

I have done this on different vehicles and it works

[demian5]

Originally Posted by Bob B.

Do you have the correct 1970 gas tank? If it does not have the vent line on top you might have a 1969 tank, or one for a 1970 without EEC. If that is the case you might want to try a 1969 cap. A truck with EEC will have the extra vent line on top of the tank and the charcoal canister under the hood.

Well the 69 cap is the same as the 70...

I have no vent lines on the tank except the fuel line for the sender.

[Fbks_Cruiser]

Do you still have the original cap? Like mine, it probably leaked because the rubber seal is old, dry and cracked. Try carefully removing the rubber seal from the new cap and putting it on the old cap.

But be warned, I had gotten a new vented cap from Stant a couple of years ago. The rubber only lasted about 1-1/2 years. Then it started to crack and leak. I guess there are different rubber compounds now a days. I cut a new seal out of some rubber I had lying around. We’ll see how long it lasts.

[demian5]

Originally Posted by Fbks_Cruiser

Do you still have the original cap? Like mine, it probably leaked because the rubber seal is old, dry and cracked. Try carefully removing the rubber seal from the new cap and putting it on the old cap.

But be warned, I had gotten a new vented cap from Stant a couple of years ago. The rubber only lasted about 1-1/2 years. Then it started to crack and leak. I guess there are different rubber compounds now a days. I cut a new seal out of some rubber I had lying around. We’ll see how long it lasts.

My understanding is the caps need to be replaced every couple of years cause of that. No big deal, I just want the right one on my truck so it works properly.

[jeffahart]

I am running a stant 10623 and it vents. I bought a couple others that did not. When you get the cap blow on the vent, it should vent.


j

[Shinysideup]

Whats too much pressure you speak of? It should hold a little, which I assume you hear when you remove the cap. You may be trying to solve a non-issue.

[54blackhornet]

I learned that NAPA caps are junk ! Bought two and the rubber dissolved in no time at all. Also learned that if you have trouble with your carb losing prime, have to pump the gas repeatedly before starting, you are probably using the wrong style gas cap....

[demian5]

Originally Posted by Shinysideup

Whats too much pressure you speak of? It should hold a little, which I assume you hear when you remove the cap. You may be trying to solve a non-issue.

It wants to blow the cap out of my hand and the cab smells like gas bad cause the pressure is trying to come out of wherever.

[demian5]

Ok, so I bought one for my truck. A 1970 and earlier 10491.

I blew through the back of it, pressure was released (unlike the 10582 I have that i can't blow through since the tank is supposed to have a vent on this model year). I think "awesome, solved!"

Put it on, make some on ramp maneuvers, gas all over side of truck.
Seems to seal, the lock mechanism is a little lazy compared to the old one... lets return it and try another one.
Replacement cap, same thing. Gas all over. Lock mechanism lazy on this one too.

Back to the cap I've had that builds up too much pressure.

I would like to see what the "hole' thing is about for the current cap. Or maybe I try a 72 cap, but that would be the same as the 71 I assume. Maybe I try and pull the pressure mechanisms out of both caps and swap them...

Ill keep trying stuff till I fix it. However, I know this has been solved by somebody.

The funniest thing I have learned about this (don't tell ANYONE) the keys interchange and work between all of the caps. Buy a cap and open your buddies gas cap...

[jcwren]

This issue with replacing gas caps every couple years, or declaring the NAPA ones are junk, is most likely because of gas with a high ethanol content. That garbage just DESTROYS rubber.

This idiotic idea of ethanol-based fuels has done far more economic damage than any environmental benefit it purportedly has. It's destroyed rubber in innumerable vehicles and small gas engines, absorbs water far quicker, turns to varnish sooner, and raised the price of corn to feed animals. Just another "good idea" from the government.

[54blackhornet]

My statement that NAPA caps are junk is correct ! The store manager agreed wholeheartedly. I also never have put anything other than NON ETHANOL premium in my two 67/72’s, and I mean ever. Both have their original engine and carbs. After pumping numerous times they both start on old style divorced chokes and run perfectly. Not being able to buy something as simple as a proper gas cap is just ridiculous. Hopefully I’ll live long enough to see the return of proper America made craftsmanship once again. And as far as rubber goes, I’ve bought gas filler rubber grommets that failed in less then two years. Never once spilled gas on them either. Same goes for brake and clutch pedal rubber, failure! Same with replacement rubber floor mats.

[697498chevy]

Car Quest #10623 works well on my 1969 also .

[Bigdav160]

I don't think you can buy a truly vented cap anymore. EPA mandated that they must hold some pressure.

I am pretty sure I read that replacement caps designed for vented applications hold 1-3 psi

[697498chevy]

The #10623 cap doesn't leak on right turns on my 69 truck . If I fill it up to the neck and park it in the sun it'll build up pressure and probably leak . I don't fill it all the way up . My truck does have a LMC tank with the vent line plugged . Hope this helps .

[jeffahart]

Originally Posted by 697498chevy

The #10623 cap doesn't leak on right turns on my 69 truck . If I fill it up to the neck and park it in the sun it'll build up pressure and probably leak . I don't fill it all the way up . My truck does have a LMC tank with the vent line plugged . Hope this helps .

My 10623 cap vents and breaths. Maybe I got a defective cap. But it does not have the same internals of other caps I've tried. I just might look at one next time I'm at O'Reilly and see if it vents. Anyhow, I finally have I cap I love. I hated the tank bloat.


j

[demian5]

Originally Posted by jeffahart

My 10623 cap vents and breaths.

I bought one of those too and still not right...

Ill drill a hole in the only one I have that doesn't leak all over the side of the truck and hold too much pressure.

[jeffahart]

Originally Posted by demian5

I bought one of those too and still not right...

Ill drill a hole in the only one I have that doesn't leak all over the side of the truck and hold too much pressure.

Interesting, your the second one who now said the Stant 10623 doesn't vent. I must have gotten a one off or something. I will test another because I'm curious. I will probably end up venting my tank in the future anyway, but the gas cap thing is making me curious.

I agree on the leaking rubber. Seems like the gas caps have to be treated as a perishable these days and replaced every couple years.

Good luck, the mod is pretty simple too though.


j

[webfoot]

I have also run non-ethanol premium in my old rides and the pressure builds up so much in these "vented" caps it swells the tank up. I went to fuel up on a hot day once on a long trip and the cap blew out of my hands and filled my face full of gas vapors.

Rubber these days is absolute garbage. My shift boots I installed a few years ago are already cracking. I see why NOS parts are so popular, cuz they are worth it. I put a new fuel neck grommet on my tank filler and that thing was so dry rotted in 1 year it basically crumbled off. Why are resellers carrying this crap?

End of rant.