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#1 |
Registered User
Join Date: Aug 2016
Location: Lake Forest, CA
Posts: 2,177
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Correct Gas Cap? Too much pressure!
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.
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"Work hard, use your vacation days." 1970 C15 GMC Long Bed 1986 C20 Scottsdale 1983 K2500 Sierra Classic Suburban 6.2 Instagram: C10sofOC |
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#2 | |
Senior Member
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Location: Los Angeles
Posts: 1,331
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Re: Correct Gas Cap? Too much pressure!
Quote:
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1967 GMC CM-2500 Camper Cruiser, 351E V-6, NP 435 4 speed, Dana 60, and factory A/C. 2012 GMC K-3500 WT regular cab, 6.0L Vortec, 6L90. |
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#3 |
Registered User
Join Date: Mar 2007
Location: cincy
Posts: 693
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Re: Correct Gas Cap? Too much pressure!
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.
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There's something women like about a pick-up man 1967 c10 swb Stepside 2004 SSR 2013 Silverado swb |
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#4 |
Senior Member
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Location: Vacaville, CA
Posts: 529
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Re: Correct Gas Cap? Too much pressure!
FRC is it possible to post a pic of the hole you drilled for reference on the cap?
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1971 Custom/10 - 350/3 speed, Orange/White roof |
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#5 |
Registered User
Join Date: Aug 2016
Location: Lake Forest, CA
Posts: 2,177
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Re: Correct Gas Cap? Too much pressure!
Pictures of this or you are telling tall tails...
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"Work hard, use your vacation days." 1970 C15 GMC Long Bed 1986 C20 Scottsdale 1983 K2500 Sierra Classic Suburban 6.2 Instagram: C10sofOC |
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#6 |
Registered User
Join Date: Mar 2007
Location: cincy
Posts: 693
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Re: Correct Gas Cap? Too much pressure!
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There's something women like about a pick-up man 1967 c10 swb Stepside 2004 SSR 2013 Silverado swb |
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#7 | |
Registered User
Join Date: Aug 2016
Location: Lake Forest, CA
Posts: 2,177
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Re: Correct Gas Cap? Too much pressure!
Quote:
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"Work hard, use your vacation days." 1970 C15 GMC Long Bed 1986 C20 Scottsdale 1983 K2500 Sierra Classic Suburban 6.2 Instagram: C10sofOC |
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#8 |
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Join Date: Dec 2009
Location: El Dorado Ca
Posts: 3,374
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Re: Correct Gas Cap? Too much pressure!
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#9 | |
Registered User
Join Date: Aug 2016
Location: Lake Forest, CA
Posts: 2,177
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Re: Correct Gas Cap? Too much pressure!
Quote:
I have no vent lines on the tank except the fuel line for the sender.
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"Work hard, use your vacation days." 1970 C15 GMC Long Bed 1986 C20 Scottsdale 1983 K2500 Sierra Classic Suburban 6.2 Instagram: C10sofOC |
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#10 |
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Location: Fairbanks, AK
Posts: 336
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Re: Correct Gas Cap? Too much pressure!
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.
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1972 GMC K2500 Super Custom Matt |
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#11 | |
Registered User
Join Date: Aug 2016
Location: Lake Forest, CA
Posts: 2,177
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Re: Correct Gas Cap? Too much pressure!
Quote:
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"Work hard, use your vacation days." 1970 C15 GMC Long Bed 1986 C20 Scottsdale 1983 K2500 Sierra Classic Suburban 6.2 Instagram: C10sofOC |
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#12 |
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Location: Scottsdale, AZ
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Re: Correct Gas Cap? Too much pressure!
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.
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#13 |
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Join Date: Apr 2012
Location: Ocala,Fl
Posts: 733
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Re: Correct Gas Cap? Too much pressure!
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.
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#14 |
Registered User
Join Date: Jul 2008
Location: Eastern Oregon
Posts: 2,337
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Re: Correct Gas Cap? Too much pressure!
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....
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71 C-20 07 Magnum RT AWD Last edited by 54blackhornet; 01-05-2019 at 04:00 PM. |
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#15 |
Registered User
Join Date: Aug 2016
Location: Lake Forest, CA
Posts: 2,177
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Re: Correct Gas Cap? Too much pressure!
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.
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"Work hard, use your vacation days." 1970 C15 GMC Long Bed 1986 C20 Scottsdale 1983 K2500 Sierra Classic Suburban 6.2 Instagram: C10sofOC |
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#16 |
Registered User
Join Date: Aug 2016
Location: Lake Forest, CA
Posts: 2,177
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Re: Correct Gas Cap? Too much pressure!
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...
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"Work hard, use your vacation days." 1970 C15 GMC Long Bed 1986 C20 Scottsdale 1983 K2500 Sierra Classic Suburban 6.2 Instagram: C10sofOC |
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#17 |
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Location: Flowery Branch, GA
Posts: 206
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Re: Correct Gas Cap? Too much pressure!
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.
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1970 C10 LWB Stepside 1971 Dodge Dart 1993 Buick Roadmaster Estate Wagon |
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#18 |
Registered User
Join Date: Jul 2008
Location: Eastern Oregon
Posts: 2,337
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Re: Correct Gas Cap? Too much pressure!
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.
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71 C-20 07 Magnum RT AWD |
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#19 |
Registered User
Join Date: Jan 2009
Location: South Carolina
Posts: 264
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Re: Correct Gas Cap? Too much pressure!
Car Quest #10623 works well on my 1969 also .
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#20 |
Registered User
Join Date: Apr 2011
Location: Klein Texas
Posts: 3,852
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Re: Correct Gas Cap? Too much pressure!
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
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My Classics: '72 K20 Suburban + '65 Dodge Town Wagon '72 Corvette Roadster +'67 Corvette Roadster '73 Z-28 Camaro '63 Ford SWB Uni Pickup '50 Ford Coupe |
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#21 |
Registered User
Join Date: Jan 2009
Location: South Carolina
Posts: 264
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Re: Correct Gas Cap? Too much pressure!
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 .
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#22 | |
Senior Member
![]() Join Date: May 2012
Location: Scottsdale, AZ
Posts: 1,906
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Re: Correct Gas Cap? Too much pressure!
Quote:
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#23 |
Registered User
Join Date: Aug 2016
Location: Lake Forest, CA
Posts: 2,177
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Re: Correct Gas Cap? Too much pressure!
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.
__________________
"Work hard, use your vacation days." 1970 C15 GMC Long Bed 1986 C20 Scottsdale 1983 K2500 Sierra Classic Suburban 6.2 Instagram: C10sofOC |
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#24 | |
Senior Member
![]() Join Date: May 2012
Location: Scottsdale, AZ
Posts: 1,906
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Re: Correct Gas Cap? Too much pressure!
Quote:
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
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#25 |
Registered User
![]() Join Date: Nov 2007
Location: Hermiston, OR
Posts: 947
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Re: Correct Gas Cap? Too much pressure!
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.
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Running in place gets you nowhere fast. -me 1968 GTO 4-spd covnvertible 1970 K-20 4-speed, factory AC. |
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