Hilljack68
Well-Known Member
Thanks Steve. My only concern with the vented is spillage on acceleration.. as my fill neck is behind the license plate. Seems like a potential for bleed-through.
Tank vent line is puking fuel
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steve340
Well-Known Member
Same as mine I have a 1968 GTX. No problem at all with with the cap under any conditions.
It can get fairly hot here in summer and the modern fuels expand like crazy.
It was a few years ago but I think the recommended cap was a 1973-75 B Body cap - but not super sure on that.
It was about 50 USD on EBAY.
It can get fairly hot here in summer and the modern fuels expand like crazy.
It was a few years ago but I think the recommended cap was a 1973-75 B Body cap - but not super sure on that.
It was about 50 USD on EBAY.
Hilljack68
Well-Known Member
Sweet. Thanks much Steve! I'll give it a go.
steve340
Well-Known Member
It should work or at least help.
If you want me to post a couple of pics of what I did to the vents I can.
You do not need to modify the car or the tank it is only rubber tubes and grommets.
I believe I modified the vents first which resolved 95% of the problems - it stopped puking liquid fuel on the ground and the stink of raw fuel was largely eliminated.
I was paranoid someone would throw a cigarette butt under the car and set the puddle of fuel it had pushed out alight and torch my car.
However there was still a slight "whoosh" noise when I removed the gas cap. Air pressure was either going in or coming out - I think it was going in. A mechanical fuel pump if there is no air able to go in to the petrol tank it will pull a vacuum in the tank and the engine can starve or you can collapse the fuel tank.
When I fitted the later model fuel cap it was 100% sorted.
If you want me to post a couple of pics of what I did to the vents I can.
You do not need to modify the car or the tank it is only rubber tubes and grommets.
I believe I modified the vents first which resolved 95% of the problems - it stopped puking liquid fuel on the ground and the stink of raw fuel was largely eliminated.
I was paranoid someone would throw a cigarette butt under the car and set the puddle of fuel it had pushed out alight and torch my car.
However there was still a slight "whoosh" noise when I removed the gas cap. Air pressure was either going in or coming out - I think it was going in. A mechanical fuel pump if there is no air able to go in to the petrol tank it will pull a vacuum in the tank and the engine can starve or you can collapse the fuel tank.
When I fitted the later model fuel cap it was 100% sorted.
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I run a vented cap on my '68 GTX - parts guy and I went through the Stant book one day looking for a suitable
one that would work AND he had in stock. In my case, it wound up being for a '73 Ford station wagon.
Ok, go ahead and tell me I shouldn't run a vented cap, experts....
one that would work AND he had in stock. In my case, it wound up being for a '73 Ford station wagon.
Ok, go ahead and tell me I shouldn't run a vented cap, experts....
Hilljack68
Well-Known Member
Yeah, I'd be interested in seeing those mods.
steve340
Well-Known Member
The quality of the pics is a bit poor but I think you will be OK.
The first thing I did was use clear plastic tube and brought the vents up in to the trunk so I could see what was happening.
I did some experiments and found that on my car at least the fuel could push up either vent tube right up to the parcel tray height and then drop out the chassis rail.
I figured out I needed to change the pressure in the vent tubes so all I did was use adapter fittings to change from the 1/4 inch vent tube size to 1/2 tube. This change in size allows the pressure in the tube to change and the tube becomes a syphon breaker.
I went from both vents up in to the car, adapted to the 1/2 inch tube, went up to the parcel tray and then down to the chassis rails on both sides in large loops. Some tubing and changing a few rubber grommets and it was done. Most of it is hidden by the spare wheel and you do not really notice the black tubes up to the parcel tray.
The first thing I did was use clear plastic tube and brought the vents up in to the trunk so I could see what was happening.
I did some experiments and found that on my car at least the fuel could push up either vent tube right up to the parcel tray height and then drop out the chassis rail.
I figured out I needed to change the pressure in the vent tubes so all I did was use adapter fittings to change from the 1/4 inch vent tube size to 1/2 tube. This change in size allows the pressure in the tube to change and the tube becomes a syphon breaker.
I went from both vents up in to the car, adapted to the 1/2 inch tube, went up to the parcel tray and then down to the chassis rails on both sides in large loops. Some tubing and changing a few rubber grommets and it was done. Most of it is hidden by the spare wheel and you do not really notice the black tubes up to the parcel tray.
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Hilljack68
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I had her out last night for a bit, and employed the same strategy. I shut down the engine, popped the cap off, it de-pressurized... and no puking. I still need to source a vented cap, but this'll work in the interim. Thanks.
Satellite Pilot
Member
Genuinely curious what the source is for this. I am in the process of installing a new tank on my 68 Sport Satellite. I am 99% sure the old tank is factory and has the short (in tank) vent tube closest to the sending unit, as well as the short external vent tube connected to it. So, short to short and long to long. I've tripple checked all of this to make sure I will install correctly which is why I'm questioning things. New tank, AMD, is the same as the old tank.
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The 100's that have done it before can't all be wrong...
If your tank is full and/or it's a hot day and/or you go up and down big hills, it always spits out a little gas here and there if it's 69ish or earlier. Only with the big gas/vapor drain tube in the trunk in the ECS CA cars in 70 or so did they start to address this. When I was in my 20's I realized that my 73 Cuda never did this. Only recently did I discover that they started putting in ways to prevent gas spillage in the early 70s. Here is a pic of the vapor separator (overflow limiting valve in the pic) from the 73 or so FSM. The separator was connected to the rear shock mount and a ball valve in the separator prevented gas from getting out and also sent the vapor to a carbon canister and a special gas cap was used to release pressure and also let in air. That's also why 72ish or newer mopars don't really smell that bad in the garage except for float bowls evaporating when parked.
70 Trunk Tube...
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Satellite Pilot
Member
Certainly wasn't trying to imply that it is wrong at all, the long to short makes sense. Just curious if there is any factory diagram that shows it. It would appear that mine was installed wrong from the factory and it makes me wonder how many others were as well.
I'm not sure about from the factory, but I "think" it would make sense that the longer tube in the tank goes to the shorter vent line on the shock tower and the shorter tube in the tank goes to the vent line that goes up into the trunk and then drains in the frame rail. Again, I'd have to look, but that would make sense to me. But I could be wrong.
Satellite Pilot
Member
I completely agree that it makes sense for them to be that way, having the two shorts connected makes it way to easy for the fuel to spit out. I'm replacing my tank because I was convinced it had a leak somewhere, recently leaving puddles in the garage. Now I'm not so sure. I've had the car 22 years and it just became a new thing. If I hadn't come poking around on here out of curiosity, I would have hooked it all back up just as it was.
DynaBro
Well-Known Member
I've had bad luck with the newer versions of vented/pressure relief gas caps. I had the wooshing sound as well with the newer caps with the plastic/yellow that goes in the tank. I found a much cheaper NORS one like in the link below when I was looking -- look at the NOS cap in the listing. It is all metal vs the yellow plastic vent. I got a NORS one and no wooshing or pressure sound when I remove the cap.
NOS Mopar Gas Cap 3549088 / 3780670 Plymouth Cuda Barracuda 1972-74 Box Dated 71 | eBay
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DynaBro
Well-Known Member
Yikes. $$$$. I'm willing to try a $10 newer one first. Thanks for letting me know that will fit though, now I can keep an eye out for one.
This this will fit?
1973-1974 Plymouth Dodge Chrysler Newport Dart Fury Fuel Gas Cap 3549087 NOS | eBay
Part Number: 3549087. Make: Plymouth, Dodge, Chrysler. We started acquiring NOS over 50 years ago and never stopped. If you need a specific part, just ask! Happy motoring!
www.ebay.com
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That looks closer/correct. Looks like you can return it too.
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