Help. Can't find venting fuel cap - The 1947 - Present Chevrolet & GMC Truck Message Board Network

BobaFett · 08-21-2017, 04:18 PM

So I want to swap from my keyed fuel cap to a plain Jane twist cap on my 70' C10 with a tank in the cab. . I read numerous threads on vented gas caps but was never able to find one with a specific part number. I have now purchased 2 gas caps that look like they vent but it still is holding a bunch of pressure. Can anyone point me in the right direction?

GASoline71 · 08-21-2017, 11:32 PM

A stock replacement fuel cap for a 1970 should be a vented cap. What brand and what part numbers did you buy?

Gary

BobaFett · 08-21-2017, 11:40 PM

ACDelco 12F7 is what Amazon said
Duralast 6023 is what Autozone said
They look identical and both boxes advertise vacuum and pressure relief but there is a bunch of pressure every time I remove the cap.

**dmjlambert** · 08-21-2017, 11:41 PM

My understanding is it is normal for them to hold a little pressure. The pressure is only from heat expansion on a hot day. If the pressure is excessive they will vent. They are vented such that they will let air into the tank if a vacuum develops, such as air comes into the tank through the gas cap vent to replace the space left from using gas. If the cap were to hold a vacuum, the truck fuel pump wouldn't be able to pull gas out of the tank for the carburetor.

BobaFett · 08-21-2017, 11:54 PM

There is a large amount of pressure in the tank. Like it is very audible when I remove the cap. With my keyed cap, there is nothing. Once the pressure builds up, you can smell gas for 5' away from the truck. Almost like it is pushing out from the seals.

Wrenchbender Ret · 08-22-2017, 02:23 PM

Drill a little hole in the cap.

**coppertone** · 08-22-2017, 04:34 PM

I had the same problem with my gas cap. I found a thread that someone created that showed how to eliminate the pressure. What I did is take the cap apart and cut the internal spring in half. That worked for me.

alsriv2 · 08-22-2017, 05:23 PM

Quote:

Originally Posted by coppertone

I had the same problem with my gas cap. I found a thread that someone created that showed how to eliminate the pressure. What I did is take the cap apart and cut the internal spring in half. That worked for me.

This is a great solution. I have the same problem as the OP. I am going to try this. Many years ago, I had a '67 GMC that poured gas out the fuel neck/cap even with new caps in place, now I have the opposite problem.

FRCvette · 08-22-2017, 05:33 PM

Quote:

Originally Posted by Wrenchbender Ret

Drill a little hole in the cap.

I did this and it fixed mine.

697498chevy · 08-23-2017, 10:37 AM

Recently put a new gas tank in my 1969 C 10 . First new cap leaked gas and had no pressure build up . Second cap didn't leak but built up a lot of pressure . Third cap doesn't leak so far and doesn't build up any pressure . It's a Carquest cap from Advance #10623 cost $6.69 . Hope this helps .

08-21-2017, 11:40 PM	#3
BobaFett Registered User Join Date: Mar 2016 Location: Livermore, CA Posts: 18	Re: Help. Can't find venting fuel cap ACDelco 12F7 is what Amazon said Duralast 6023 is what Autozone said They look identical and both boxes advertise vacuum and pressure relief but there is a bunch of pressure every time I remove the cap.

08-21-2017, 11:41 PM	#4
dmjlambert Senior Member Join Date: Apr 2016 Location: Cypress, TX Posts: 3,923	Re: Help. Can't find venting fuel cap My understanding is it is normal for them to hold a little pressure. The pressure is only from heat expansion on a hot day. If the pressure is excessive they will vent. They are vented such that they will let air into the tank if a vacuum develops, such as air comes into the tank through the gas cap vent to replace the space left from using gas. If the cap were to hold a vacuum, the truck fuel pump wouldn't be able to pull gas out of the tank for the carburetor.

08-21-2017, 11:54 PM	#5
BobaFett Registered User Join Date: Mar 2016 Location: Livermore, CA Posts: 18	Re: Help. Can't find venting fuel cap There is a large amount of pressure in the tank. Like it is very audible when I remove the cap. With my keyed cap, there is nothing. Once the pressure builds up, you can smell gas for 5' away from the truck. Almost like it is pushing out from the seals.

08-22-2017, 02:23 PM	#6
Wrenchbender Ret Registered User Join Date: Oct 2005 Location: Overland Park, Ks. Posts: 5,229	Re: Help. Can't find venting fuel cap Drill a little hole in the cap.

08-22-2017, 04:34 PM	#7
coppertone Active Member Join Date: Feb 2011 Location: Deep South Texas Posts: 116	Re: Help. Can't find venting fuel cap I had the same problem with my gas cap. I found a thread that someone created that showed how to eliminate the pressure. What I did is take the cap apart and cut the internal spring in half. That worked for me. Attached Images

08-21-2017, 04:18 PM	#1
BobaFett Registered User Join Date: Mar 2016 Location: Livermore, CA Posts: 18	Help. Can't find venting fuel cap So I want to swap from my keyed fuel cap to a plain Jane twist cap on my 70' C10 with a tank in the cab. . I read numerous threads on vented gas caps but was never able to find one with a specific part number. I have now purchased 2 gas caps that look like they vent but it still is holding a bunch of pressure. Can anyone point me in the right direction?

08-23-2017, 10:37 AM	#10
697498chevy Registered User Join Date: Jan 2009 Location: South Carolina Posts: 266	Re: Help. Can't find venting fuel cap Recently put a new gas tank in my 1969 C 10 . First new cap leaked gas and had no pressure build up . Second cap didn't leak but built up a lot of pressure . Third cap doesn't leak so far and doesn't build up any pressure . It's a Carquest cap from Advance #10623 cost $6.69 . Hope this helps .



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