Need help with fuel tank venting on CJ3a

[JimW]

Hi.  I'm having some fuel tank problems and I'm hoping someone on here can help me.  First, I have a '49 CJ3A.  For various reasons, I decided to replace the gas tank.  In doing that, I discovered that the tank did not fit as well as the one that I took out (an threw away).  To make a long story short, I ended up having to use a metal pipe to bend the filler neck down so that I could slide the tank closer to the side of the jeep.  The original tank (at least the one that was in it when I bought it) had no problem with this. My gas cap is the standard original type replacement which is vented, I believe. As a result, with the lower fill neck, the gas cap leaks pretty bad on a right hand turn, until the level goes down considerably.  I think the best solution is to go to a non-venting gas cap and then add a vent hole to the tank. As I was looking for parts, it came to me that I could drill a hole in the top of the sending unit, maybe 1/16th inch or so.  I know that it's possible that gas could leak out on a rollover, but I have that issue now. I don't think I would get much, if any, gas coming out of the top from the hole. I want to know what you guys think about this idea.  Stupid?  It would save the me trouble of pulling the tank, drying it out, and welding in a bung for the vent valve.  Of course, if it doesn't work out, all I have to do is replace the sending unit that's bolted to the top of the tank.  Thoughts and ideas would be appreciated.  Thanks.

[aboyandhisdog]

I'm no authority on this but I'm pretty sure that your cap shouldn't be leaking like you describe, even though it is a vented cap.  Is the cap gasket in good shape and sealing well? 

As for drilling the sender, don't do it.  Any hole, opening, or poor gasket on the top of the tank will most definitely leak gas all while you are driving and the smell will drive you nuts too.  You'll have a real mess on your hands. 

If a new cap or cap gasket doesn't solve the issue, I would bite the bullet and drain the tank and install a proper vent fitting in the top of the tank.  I have an M38 tank and it has one of these vents so I would think they are available somewhere. 

[1955CJ-5]

I agree with Tom.....I've had poor fitting or old gaskets on the sending unit and those would leak..so plenty of fuel sloshing around in there...

The vented Eaton caps are supposed to have a small spring loaded valve inside to seal them from leaking....the valve may have just been wishful thinking though...but you might shake your cap and see if it rattles...cleaning the cap with carb cleaner or lacquer thinner might loosen the valve....

[athawk11]

My first thought is that if the vented cap isn�t sealing the tank, why would the non-vented cap work?

I agree with the others.  The constant smell of the venting gas in the cab area would drive me crazy..  These things already stink.  (The exhaust seems to swirl back into the cab.)

You might try this.  I picked up a rubber ring at Ace Hardware and added it to my cap. My original cap gasket was a bit tired so it leaked. The extra rubber ring helped quite a bit.  It only dribbles a bit on an incline with the tank overfilled.

You can see the edge of the ring in this photo.  The diameter of the ring was a bit larger than the cap.  The cap is a little more difficult to get back on, but I can live with that.  What I couldn't live with was the gasoline screwing up my paint.

 

[Bob W]

Original caps are vented - but it takes a slight bit of pressure to open the spring loaded valve. It shouldn't leak when going around a corner. I think a lot of aftermarket caps do not have the proper valves inside. Learn more about gas caps here....
http://www.cj3a.info/tech/gascap.html

[1955CJ-5]

Hi Bob,

Looking at that link it seems there are two valves in the Eaton cap, located together on that center "button'...a pressure relief valve, and the smaller vacuum relief valve....

Is that right?

[Bob W]

Yes, there are two valves. The small vacuum valve and spring are inside the larger pressure valve.

[Oilleaker1]

A friend tried two caps. Original type. My original did not leak on mine, even when cornering. It did leak on my friends Jeep. What we discovered was the filler lip or top flat surface had a low spot in it that the cap gasket would not seal against. Another thing to examine! John

[Bob W]

I've seen that problem with some reproduction tanks. The latest one I got from Walcks is much better.

[JimW]

Hi guys.  Thanks for all of the responses. I forgot to mention that I added a cork gasket to the cap, along with the rubber gasket it came with.  The cap is now hard to put on, but it does turn fully. I think it's as good of a seal as I can get. I have not checked for the flatness of the tank at the cap interface.  I'll take a look at that. I have read that the new reproduction caps don't have the check valves and I have read of other people who have a leaking cap that they believe is due to the cap vents.  Back to the idea of putting a hole in the sending unit plate, my thought was that, while driving, the vent direction is from the outside to the inside of the tank as the fuel pump pulls in the gas and the air enters to replace that volume.  If so, then there shouldn't be any gas fumes inside while driving.  The problem, I think, would be when the engine is off and the tank heats up, causing gas fumes to want to be pushed out of the vent hole. In that case, I may not care.  I think I'm going to try my idea and see what happens. The worst that can happen is that I have to buy another sending unit, which isn't that bad. If it doesn't work out, then I'll pull the tank and weld in a bung for a vent tube, or some other type of vent valve that requires a hole to be drilled.  Not sure what's really available yet.  Also, going to a non-vented cap will tell me if the leak problem is the cap seal (gasket) or really is the vent hole path. 

[Bob W]

I think fuel will slosh out of any hole in the top of the tank while you are driving.

Why not drill and tap (1/8" pipe thread) a hole in the sender? Then plumb a vent to the engine compartment, similar to the CJ-V35 fuel tank venting system.

[aboyandhisdog]

Jim, take it from a guy who has been there with a bad sender gasket - gas will slosh out of that hole!

[JimW]

You guys make some good points.  The reason that I thought gas would not slosh out of the hole is because the sending unit has a, for lack of a better word, a cylinder attached to the underside of the sender plate.  This cylinder has a hole in the bottom so I thought that would form a "natural" splash shield.  This would not be the case for the sender plate gasket around the edges, which "sees" the gas at all times. However, I am interested to learn more about the CJ-V35 venting system mentioned by Bob W.  I had thought about a similar idea, but I was thinking that I the sender plate was too thin to actually tap.  Maybe that's not the case.  Where can I get more info on the CJ-V35 vent system?  Thanks.

[JimW]

OK, I found information about the CJ-V35 and it's venting design. Looks like that jeep was meant to run partially submerged.  I just ordered a panel mount (i.e. UNF thread, not pipe) right angle 1/8" hose barb.  I can either mount it on the sender plate, or, I can just drill a hole next to the sender opening, remove the sender, install the hose barb, and run a hose up into the engine compartment.  Probably could also install one of those vent check valves so it won't spill fuel in the event of a roll over.  I like this idea a whole lot better than my earlier idea. Thanks, guys.  Really, my biggest motivation is to NOT take out the gas tank again. It just doesn't fit right, so it was more of a pain than it should have been. 

[mtnman37879]

Just remember, the back side of an engine is a pump. Venting the gas tank to the crankcase will work but if the crankcase vent were to get clogged the back pressure will go to the gas tank spewing gas out the filler.