Help School Me About Gas Tank Caps

Here is the gas cap that came on my Jeep ( it had a Bubba made tank - I sourced a donor tank from a 1960s CJ6 from a member here).

Shown next to it is a brand-new Stant chrome gas cap.


To my eye neither of these is vented, am I right? Or is the hole in the Bubba tank cap the vent?

What makes a gas cap Vented versus not Vented?

 

Somewhere inside the black cap may be a one way valve, to relieve vacuum in the tank as the gas is consumed. See those 4 dimples around the inside of the rim?

I once had a J-truck gas tank implode when the vent was damaged

 

What your calling “Bubba” is the OEM cap.
These are very good caps if the gasket is kept in shape.

 

I meant the tank - it was homemade. Whomever made it must have kept the OEM cap then?

 

And don’t get me wrong - who ever made a gas tank out of 1/8” plate and put it in my Jeep was a pretty darn talented fabricator.

 

So do the two dimples on the Stant cap give it venting abilities?

 

Oh my bad , I thought it had a bubba cap too.
That’s what I get for taking Bubbas speed reading course.

 

https://www.oreillyauto.com/detail/...tant-oe-equivalent-vented-fuel-cap/sta4/10625

 

???
The crimps in the black cap provide air bypasses. I'm not seeing anything like that on the Stant.

 

"So do the two dimples on the Stant cap give it venting abilities?"

Yes, I have the Stant vented caps on my Jeeps and they work fine.

 

Vented in, but not out. Back pressure/fuel can be released when opening, if you are a lawyer.

But I'm not sure that all Stant caps are vented, or even that the OP's is.

 

That new cap does not look vented to me, the gasket squeezes down on the neck lip, I don't see how it could let it vent? On My Jeep the cap leaks. I don't fill it all the way up, if I park it side hill as the gas warms up and expands, it will leak gas out the cap. Just a Thought.

 

All I know is that I tore one apart once, and found a tiny spring loaded check valve.

 

Me too, it used to leak if the tank was close to full and parked on a hill.

 

Every Jeep I have ever owned would leak if parked on a hill with a near full tank regardless of what cap it had on it.

I think it is just a "Jeep Thang".

 

Many of the "old timers" (and I say that with maximum respect as a term of endearment) would say that Jeeps marked their territory with a variety of fluids.