Gas tank vent? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

OJ1988 · 10-07-2009, 08:32 PM

Background. Truck is a 1969 250 6cyl 3 speed, original. Original tank.

The paint was gone under the gas filler when I got the truck. Figured it was from people overfilling, but learned the the gas cap was not sealing and gas would run out of tank when making hard right turns.

Went to OReillys and got a new cap.

It sealed much better, and gas no longer leaks.

Now, when ever I take the cap off, there is a major whoosh sound and sometime you here the tank pop, like its getting sucked in.

So, I guess the tank is no longer venting.

Did they give me the wrong cap?

Is there a vent somewhere else that I need to check for?

cdowns · 10-07-2009, 08:38 PM

they gave you the wrong cap// you need a vented tank cap. the cap you have is correct for the later 71-72trucks

OJ1988 · 10-07-2009, 08:39 PM

thanks!

OJ1988 · 10-23-2009, 11:38 AM

Well I double chacked it.

Got the right gas cap. It is vented.

I looked at the tank in the truck and do not see a vent.

I have been putting the cap on, and not tightening it all the way.

FWIW, I checked 2 different parts stores, looked a 4 or 5 different caps.

**LockDoc** · 10-23-2009, 03:02 PM

-
Are you going by the box or does it say vented on the cap? I would try another brand of vented cap. I would say the cap has to be mis-labeled or defective.

LockDoc

OJ1988 · 10-26-2009, 09:53 PM

I looked at the cap. Looked up models for 70 and 72 and compared mine to ones from auto zone and oriellys

unclewatts · 10-26-2009, 11:54 PM

Quote:

Originally Posted by LockDoc

-
Are you going by the box or does it say vented on the cap? I would try another brand of vented cap. I would say the cap has to be mis-labeled or defective.

LockDoc

Lockdoc is right. The cap can't be vented and create a vacuum in the tank. The cap is wrong or it is defective. period.

OJ1988 · 10-29-2009, 07:43 PM

Well,

I went to Auto ZOne and bought another cap(first one came from oriells)

Still doing the same thing.

?????????????????????

unclewatts · 10-30-2009, 05:50 AM

This doesn't make sense. If the cap is vented then it can't create a vacuum. The only conclusion I can come to is that the new cap you bought isn't a vented cap. Maybe it's the wrong cap and somehow it's prevented from venting because of the way it fits on the neck of the tank.

OJ1988 · 10-30-2009, 09:13 AM

You're telling me. I just finished building a 455 Olds for a guy, yet I can't seem to get my gas cap on right!

This is the cap,

http://www.autozone.com/autozone/cat...questid=197231

Looks just like the first one I got from Oriellys as well.

fdbdw · 11-01-2009, 12:12 PM

hey OJ1988,
did your figure anything out yet, I just bought a new vented cap and am having the same issue, never happend with the old cap, I was wondering if gas had sloshed into the vent after I filled up and plugged the vents, anyway I put the old cap on and let the new one dry out and am gonna try it out today and see what happens, kinda wierd

bitchin85 · 11-01-2009, 01:23 PM

whats wrong with not having a vented cap.. i bought my truck with a non vented one and i hear the same noise when i take off my cap. is there anything wrong with that?

**John Fabris** · 11-01-2009, 01:36 PM

creating a vacumn in the tank means now your fuel pump has to work harder to pull fuel.

bitchin85 · 11-01-2009, 01:41 PM

would i notice any differance if its vented or non vented

BAGNDRAGIT · 11-01-2009, 01:46 PM

yea, the sound will go away.
and you may have to replace a fuel pump a lil sooner.

you have to have a vented cap on a non-vented tank.

haysonj · 11-01-2009, 01:53 PM

Quote:

Originally Posted by *****in85

whats wrong with not having a vented cap.. i bought my truck with a non vented one and i hear the same noise when i take off my cap. is there anything wrong with that?

If the fuel pump pulls enough vac on the tank it will collapse the rubber fuel lines and you will not get gas to the carb.

OJ1988 · 11-10-2009, 10:36 PM

Well, maybe the parts suppliers got a bad batch of caps? I've tried 3, and another guy here having the same problem.

haysonj · 11-11-2009, 08:24 AM

Quote:

Originally Posted by OJ1988

Well, maybe the parts suppliers got a bad batch of caps? I've tried 3, and another guy here having the same problem.

You can check the cap buy sucking on the hole on the under side. You should be able to suck air through it but not blow through it

10-07-2009, 08:32 PM	#1
OJ1988 Just a car guy Join Date: Feb 2006 Location: New Washington, IN Posts: 991	Gas tank vent? Background. Truck is a 1969 250 6cyl 3 speed, original. Original tank. The paint was gone under the gas filler when I got the truck. Figured it was from people overfilling, but learned the the gas cap was not sealing and gas would run out of tank when making hard right turns. Went to OReillys and got a new cap. It sealed much better, and gas no longer leaks. Now, when ever I take the cap off, there is a major whoosh sound and sometime you here the tank pop, like its getting sucked in. So, I guess the tank is no longer venting. Did they give me the wrong cap? Is there a vent somewhere else that I need to check for? __________________ 1955 belair Blown Pro Street cruiser 1971 Camaro Pro Touring 1973 Vega Drag Car 1970 C20 tow rig

10-07-2009, 08:38 PM	#2
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	Re: Gas tank vent? they gave you the wrong cap// you need a vented tank cap. the cap you have is correct for the later 71-72trucks __________________ 71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY

10-07-2009, 08:39 PM	#3
OJ1988 Just a car guy Join Date: Feb 2006 Location: New Washington, IN Posts: 991	Re: Gas tank vent? thanks! __________________ 1955 belair Blown Pro Street cruiser 1971 Camaro Pro Touring 1973 Vega Drag Car 1970 C20 tow rig

10-23-2009, 11:38 AM	#4
OJ1988 Just a car guy Join Date: Feb 2006 Location: New Washington, IN Posts: 991	Re: Gas tank vent? Well I double chacked it. Got the right gas cap. It is vented. I looked at the tank in the truck and do not see a vent. I have been putting the cap on, and not tightening it all the way. FWIW, I checked 2 different parts stores, looked a 4 or 5 different caps. __________________ 1955 belair Blown Pro Street cruiser 1971 Camaro Pro Touring 1973 Vega Drag Car 1970 C20 tow rig

10-23-2009, 03:02 PM	#5
LockDoc The Older Generation Join Date: Aug 2006 Location: Montezuma, Iowa Posts: 25,464	Re: Gas tank vent? - Are you going by the box or does it say vented on the cap? I would try another brand of vented cap. I would say the cap has to be mis-labeled or defective. LockDoc __________________ Leon Locksmith, Specializing In Antique Trucks, Automobiles, & Motorcycles (My Dually Pickup Project Thread) http://67-72chevytrucks.com/vboard/s...d.php?t=829820 - Last edited by LockDoc; 10-23-2009 at 03:03 PM.

10-26-2009, 09:53 PM	#6
OJ1988 Just a car guy Join Date: Feb 2006 Location: New Washington, IN Posts: 991	Re: Gas tank vent? I looked at the cap. Looked up models for 70 and 72 and compared mine to ones from auto zone and oriellys __________________ 1955 belair Blown Pro Street cruiser 1971 Camaro Pro Touring 1973 Vega Drag Car 1970 C20 tow rig

10-29-2009, 07:43 PM	#8
OJ1988 Just a car guy Join Date: Feb 2006 Location: New Washington, IN Posts: 991	Re: Gas tank vent? Well, I went to Auto ZOne and bought another cap(first one came from oriells) Still doing the same thing. ????????????????????? __________________ 1955 belair Blown Pro Street cruiser 1971 Camaro Pro Touring 1973 Vega Drag Car 1970 C20 tow rig

10-30-2009, 05:50 AM	#9
unclewatts 70 Chevrolet=Obsession Join Date: Jun 2009 Location: nice ca Posts: 1,067	Re: Gas tank vent? This doesn't make sense. If the cap is vented then it can't create a vacuum. The only conclusion I can come to is that the new cap you bought isn't a vented cap. Maybe it's the wrong cap and somehow it's prevented from venting because of the way it fits on the neck of the tank. __________________ I'm Just like my truck. Old, Ugly and Grouchy. Except my truck starts easily in the morning and doesn't smoke! IT'S NOT EASY BEING GREEN! -Kermit the frog 1970 Chevrolet C-10 Longbed Stepside : 350, Muncie M20, 3.08 GM corp. positraction Forest green exterior/light green interior(Where all my money goes) 1996 Toyota Corolla (Parts runner)

10-30-2009, 09:13 AM	#10
OJ1988 Just a car guy Join Date: Feb 2006 Location: New Washington, IN Posts: 991	Re: Gas tank vent? You're telling me. I just finished building a 455 Olds for a guy, yet I can't seem to get my gas cap on right! This is the cap, http://www.autozone.com/autozone/cat...questid=197231 Looks just like the first one I got from Oriellys as well. __________________ 1955 belair Blown Pro Street cruiser 1971 Camaro Pro Touring 1973 Vega Drag Car 1970 C20 tow rig

11-01-2009, 12:12 PM	#11
fdbdw Registered User Join Date: Jan 2009 Location: colorado springs Posts: 479	Re: Gas tank vent? hey OJ1988, did your figure anything out yet, I just bought a new vented cap and am having the same issue, never happend with the old cap, I was wondering if gas had sloshed into the vent after I filled up and plugged the vents, anyway I put the old cap on and let the new one dry out and am gonna try it out today and see what happens, kinda wierd

11-01-2009, 01:23 PM	#12
bitchin85 Registered User Join Date: Aug 2009 Location: Lambertville MI Posts: 962	Re: Gas tank vent? whats wrong with not having a vented cap.. i bought my truck with a non vented one and i hear the same noise when i take off my cap. is there anything wrong with that? __________________ "I'll keep my guns, money, and freedom. You can keep the "change"

11-01-2009, 01:36 PM	#13
John Fabris TOTY 2006 Join Date: Dec 1999 Location: Magalia CA USA Posts: 2,270	Re: Gas tank vent? creating a vacumn in the tank means now your fuel pump has to work harder to pull fuel. __________________ John Fabris 67 C10 SWB

11-01-2009, 01:41 PM	#14
bitchin85 Registered User Join Date: Aug 2009 Location: Lambertville MI Posts: 962	Re: Gas tank vent? would i notice any differance if its vented or non vented __________________ "I'll keep my guns, money, and freedom. You can keep the "change"

11-01-2009, 01:46 PM	#15
BAGNDRAGIT Just Not Low Enough! Join Date: Mar 2009 Location: Phoenix, AZ Posts: 525	Re: Gas tank vent? yea, the sound will go away. and you may have to replace a fuel pump a lil sooner. you have to have a vented cap on a non-vented tank. __________________ NEED ELECTRICAL HELP? ASK ME! 67-72 Full Wiring Diagrams Lots Of Info, TAKE A LOOK 1967 Chevy C-10 Shortbox Bagged 327 4spd Previous: 1971 Chevy C-10 Short Sep I6 Auto (Traded) 1973 Chevy C-20 THE REDNECK BATTLE TRUCK 2001 Chevy Silverado 2Dr 5.3L Shortbox. R.I.P. 1969 Volkswagen Bug This is my first meeting, I have a horsepower problem.

11-10-2009, 10:36 PM	#17
OJ1988 Just a car guy Join Date: Feb 2006 Location: New Washington, IN Posts: 991	Re: Gas tank vent? Well, maybe the parts suppliers got a bad batch of caps? I've tried 3, and another guy here having the same problem. __________________ 1955 belair Blown Pro Street cruiser 1971 Camaro Pro Touring 1973 Vega Drag Car 1970 C20 tow rig



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