fuel tank gas cap
 

In my 69 pickup, I recently got a gas cap for a 69 3/4 ton from LMC. When I take the cap off, you could hear air being sucked in or out. I figured they gave me the wrong gas cap.

So I got another one from another company while at the goodguys show. It has a blue vent thing in the middle (inside) of the cap. When I took it off, same thing.

What's up with this?

Re: fuel tank gas cap
 

If you have the correct cap it should have a hole in the middle with that has a spring loaded plunger valve. This regulates the tank pressure which usually is around 3psi if I remember correctly.

The hole is about 3/16th (plus or minus) of an inch and if you insert a small object you can feel the spring loaded vent cap moving.

http://67-72chevytrucks.com/vboard/a...1&d=1313378255

Re: fuel tank gas cap
 

you should b able to get the right cap at about any autoparts store

Re: fuel tank gas cap
 

that's normal. if you unscrew the cap on a new car, it does the same thing. the newer cars also have a warning stating "Caution, contents may be under pressure"

Re: fuel tank gas cap
 

you sure nightmare, cause I can hear my tank contract when i take mine off too LOL

Re: fuel tank gas cap
 

very strange mine started doing it too! changed the cap and still does it occasionally.

Re: fuel tank gas cap
 

For YEARS I had been tryting to locate a "CHROME",
Locking Gas Cap for my 72GMC.
Everyone listed one for UP TO a 71 (but not 72).
I bought probably 3 different types, and NONE of them fit.
Either the "Tangs" would be off or the "Body" of the Cap, was too big.

I finally gave up and went to Kragens and bought a Locking Gas Cap for my 72.
Iwhen the gut pulled it out of the Box, it was CHROME (w/Blue Ring) as you described.
I was happier than "White On Rice".
Mine had the EEC too.
Just thought I'd share.;)

Re: fuel tank gas cap
 

I have posted about this before, I bought 4 or 5 caps from various sources and never could find the right one.
http://67-72chevytrucks.com/vboard/s...d.php?t=366184


Swapped yo a vented blazer tank so it's not a concern for me now.
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Re: fuel tank gas cap
 

I looked at my first "new" gas cap last night and it has this set up in it. I poked something down in it to see if it was spring loaded. It kinda caught on something, and then you could feel the spring.

Oh well....maybe this is just the way they're supposed to be. And maybe we're just used to old gas caps that the seal is worn out, so it doesn't pressurized.

Re: fuel tank gas cap
 

The cap is the vent. It has to vent or these tanks will get a vacum in them.