Fuel Cap

[Chuck W.]

My 1964 CJ3B has started having issues that I think are related to the gas tank cap. The old cap was a sloppy fit and spilled gas. I replaced it with a new cap that is a very tight fit. I suspect the fuel pump is pulling a vacuum on the tank. The engine will quit, and when I open the cap, I can hear air.
Bottom line, I need to find a vented cap that won't leak fuel on the side of the jeep.   I have only found one cap that specifically says it is vented, but it says it fits 1946 - 1963 Jeepster, Station Wagon and truck.  Does anyone know if this cap will fit a CJ3B or does anyone know of a vented cap for this jeep?
Thanks!

[Rus Curtis]

Chuck,
I couldn't find anything on this forum (nothing on Tapatalk either).  This was discussed on the 2A forum.

https://www.thecj2apage.com/forums/remote-fuel-tank-vent_topic54430_page1.html?KW=vented+cap

I found a link on the second page to armyjeepparts.  I'd been looking at that cap recently - the one with the chain on it. Note where they discuss the gasket and a link for that too.  The parts numbers don't match what I see in my PM but the 2A/3A/3B tanks are "supposed" to all be the same - I'd think it should fit.  I'm not familiar with jeepsters, trucks or wagons so I don't have any idea what size they are.

Since I'd already bought a cap from Walck's a long while back, I installed that.  I haven't done anything yet to slosh, so haven't done any extreme testing but it seems ok. 

[Chuck W.]

Thanks, Rus:
In my December 65 Jeep Universal Parts List, it shows 3 gas caps for the CJ3B; #908593, #933586 (chrome) and #931662 (locking).
Several different parts vendors list the #908593 cap as non-vented, chrome.
Kaiser Willys lists a #640594 cap as vented, black.
I don't remember where the cap I have came from, but it was probably Walck's, it is black and looks just like the picture of the #640594 in Kaiser Willys on-line catalog. I can't tell if it has a check valve or not.
The #640594 is $27.99 while the #908593 is only $15.99
Clear as mud?  Tomorrow I will gather up all the gas caps I have and see if I can find a vented one. I think I have two more black ones and at lease one chrome one.

[Chuck W.]

This gets really confusing! I looked at the #640594 cap at several of the vendors and some say it is vented and some say it is non-vented!
My original black cap appears to be the vented type, but the vent slots in the side of the cap look like they are full of rust and one of the locking tangs is bent pretty bad. This one was leaking.
The new black cap that is on it now is also suppose to be vented, but when I shake it, I can gear things rattling around inside it. This is the one that I suspect was causing a vacuum in the tank.
Long story short, I ordered the small-mouth military cap with the chain that was referenced in the link to the discussion on the 2A forum.
Time will tell!

[Rus Curtis]

I looked at the #640594 cap at several of the vendors and some say it is vented and some say it is non-vented!
My original black cap appears to be the vented type, but the vent slots in the side of the cap look like they are full of rust and one of the locking tangs is bent pretty bad. This one was leaking.
The new black cap that is on it now is also suppose to be vented, but when I shake it, I can gear things rattling around inside it. This is the one that I suspect was causing a vacuum in the tank.

I've heard the same thing AND also some that bought what they thought were vented, turned out to be not-vented.  Some others were just open, without a valve.

[BillT]

Reminds me of the pcv valve I bought once, no parts inside it!

[Chuck W.]

Looks like the small mouth military cap is going to work just fine. It is very heavy-duty and is vented with check valves.