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Topic Summary

Posted by: JimW
« on: April 16, 2017, 10:29:06 PM »

Hi everyone,
I wanted to let you know what I did and what was the outcome.  First off, I now have 3 different gas caps. One is the cap that was on the jeep when I got it. It is old but not an OEM cap. Similar, but slightly different.  The 2nd cap is an OEM reproduction.  Both of these caps are vented. The 3rd cap is one I just picked up from NAPA. It has a chrome top. The box says it's vented, but I can't see any vent holes in the cap.  I tried all three caps with any played with different arrangements of the gaskets.  All 3 leaked.  I had picked up a 1/8" right angle double hose barb that mounts with a nut on the body.  This was not pipe thread type mount but, rather, a UNF thread with nut. I removed the gas sending unit.  I thought I could drill a hole in the top, but the underside of the mounting has a cylindrical part that's attached to the plate. There is a hole in the cylinder, but it wasn't big enough to get a wrench on the hose barb.  I ended up cutting a section of the cylinder out and then drilled a hole in the mounting plate. I mounted the hose barb then replaced the sending unit.  I suspected that since the gas caps were so tight on the tank, I was getting as coming out of the vent hole. I decided to take the original cap and put epoxy over the vent hole.  After letting the epoxy cure, I replaced the gas cap and took the jeep for a drive.  Success!  I did not get any gas coming out of the gas cap. Further more, I did not get any gas coming out of the hose barb. As of right now, I have not put a hose on the barb on the sending unit. I may add that in the near future.  Taking the jeep for a long drive, I did not have any issues, so I must assume the gas tank is venting properly.  I think I'm about to declare victory on this one.  I think there are probably 2 problems with the gas cap, insufficient seal with the gasket and gas coming out of the vent hole(s).  Currently, the gas cap I'm using has 2 gaskets, the original one which is starting to dry out and another one I took off the new OEM style cap that I purchased recently.  So far, so good.  Thanks for all of your experience and suggestions.

Best Regards.........
Posted by: mtnman37879
« on: March 28, 2017, 02:25:09 PM »

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.
Posted by: JimW
« on: March 28, 2017, 12:56:53 PM »

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. 
Posted by: JimW
« on: March 28, 2017, 09:18:08 AM »

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.
Posted by: aboyandhisdog
« on: March 27, 2017, 11:57:02 AM »

Jim, take it from a guy who has been there with a bad sender gasket - gas will slosh out of that hole!
Posted by: Bob W
« on: March 27, 2017, 08:50:33 AM »

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.
Posted by: JimW
« on: March 27, 2017, 01:32:54 AM »

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. 
Posted by: Bob W
« on: March 25, 2017, 07:47:36 PM »

I've seen that problem with some reproduction tanks. The latest one I got from Walcks is much better.
Posted by: Oilleaker1
« on: March 25, 2017, 06:27:51 PM »

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
Posted by: Bob W
« on: March 25, 2017, 06:19:06 AM »

Yes, there are two valves. The small vacuum valve and spring are inside the larger pressure valve.
Posted by: 1955CJ-5
« on: March 24, 2017, 09:47:51 PM »

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?
Posted by: Bob W
« on: March 24, 2017, 04:16:29 PM »

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
Posted by: athawk11
« on: March 24, 2017, 12:49:26 PM »

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.

 

Posted by: 1955CJ-5
« on: March 24, 2017, 12:20:23 PM »

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....
Posted by: aboyandhisdog
« on: March 24, 2017, 11:59:05 AM »

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.