gas cap

The final assembly is on for my 57 CJ5 with a 283. I purchased a new stock gas tank and gas cap and have them installed. I am having some problems with the stock non-vented gas cap. Does anyone know where to get a vented locking gas cap that would fit the stock tank for a 57? Will any locking vented gas cap work?
Thanks,
Paul

 

how was the original style vented? Or was it?

 

The original cap was vented. Only gas tanks with a vapor recovery system are not vented through the cap. There was no vapor recovery system on CJs until the tank was moved to the rear in 1970.

I expect that every cap you can get for that application will be vented.

 

The cap I got from Krages is non-vented (no vented listed for the 57 ). I can't find a vented cap for the stock tank from any of the standard sources. They are all non-locking non-vented. They are not listing the original caps as vented.

 

Well, without a vented cap, there is nowhere for the fumes to go. It's been a while since I've handled those parts, but I'm sure the original cap is vented.

I wonder if they would list vented/non-vented for this application when you have no choice? The only time you would deviate from what the factory used is when you cap or remove the factory vapor recovery on a tank so equipped.Then you have to have a vented cap, otherwise the fuel pump will not function against the sealed tank - air has to get into the tank to replace the volume of gas removed.

<edit> If you'd like to post a pic of the underside of the cap, I can probably tell you if it's vented or not.

 

I can get one, but close inspection previously showed no vent. There is one I see that is black and vented. I would prefer a locking one though (some deterrent). I bought the chrome one.
Bought.. http://www.jeepdoc.com/catalog/partframe.asp?id=81

Black http://www.jeepdoc.com/catalog/partframe.asp?id=5829

 

timgr--I have a related question on the gas cap that you will know. I have the original cap for my 67 v6 jeep and i recently replaced the seal thinking that would help keep gas from spilling out when on a side hill or going around a corner. It did not work. There is a pin hole on the top and the Napa replacement cap did not have that. I just took the seal off the new one and put it on my old cap. It still leaks out gas on a side hill. ANything I can do to prevent this?

Thank you,

Peter

 

The pin hole is a labyrinth in the top of the cap that is supposed to keep gas from coming out. The design of the labyrinth varies from mfr to mfr. In my experience (IME), the seal does not work well. I tried to seal one of these tanks by plugging the labyrinth with epoxy, and vent through a tube in the filler neck, but I was not very successful at sealing the cap. Gas would still come out around the edges of the cap.

You may be more successful than I was - the seeping around the cap didn't bother me that much. Was a looong time ago ...

 

I kinda don't believe what is implied by the sticker on the chrome cap.

It would be easy to test it. Try blowing into the fuel pickup and see if air comes out around the cap. The seal of a non-vented cap is pretty good ... the fumes will build up and you'll get a whoosh when you take the cap off - this is the vapor pressure of the gasoline.

 

BTW the black cap looks like what Stant sold for many years - it may actually be a Stant. We sold the Stant cap under the Jeep PN - cheaper from Stant. Still leaked.

 

The difference is probably because I used the cheap Stant cap. I could seal the labyrinth, but it leaked around the edges.

 

So does anyone know of a locking cap for the 57 CJ5? A universal one?

 

There was a locking cap available in the day ... but if Walck's doesn't offer one, I'd guess it's NLA (no longer available).

 

The vent is there twofold. One to allow expansion and contraction of the fuel based on temperature (pressure build up, vacuum build up) and allow atmospheric pressure into the tank as the fuel level drops. If there is no provision for allowing pressure equalization as the fuel level drops (vacuum build up) then the engine could potentially starve for fuel. Patrick, how did you fix this? Do you have a return line that takes care of this or is there just enough leakage around the cap to accomodate it? I've had to fix several "antique" vehicles because of this by adding a vent in the fuel system or installing a vented cap.

I'm going to an MTS tank but want to make sure I'm not gonna starve for fuel by vacuum build up if I seal the cap really well....

 

Perfectly!

De ja vu! I think we had this conversation a couple years back?

 

This might fit (?) Twist on, not threaded.

http://store.bobdrake.com/19locgascap1.html

 

I too put a nipple in the filler neck, but this was a steel tank - a Jeep parts department item. I used the late under seat tank and even plumbed the fuel return into the proper tank. I added a under-seat tank as an auxiliary tank, and my Jeep already had a vapor recovery system. I plumbed the tank vent into the existing vapor recovery. Maybe it worked ... I didn't put enough effort into stopping the cap from seeping.