Gas Tank vent

[neilvonarb]

So now I'm the expert?

The answer is "no" it won't work. The M1A1 stainless tank is a work of art. It is the best made fuel tank for a Bronco that you can buy with money. I have purchased and installed several. The guy that designed the tank vent needs to be taken out behind the shed and beaten with a stick.

As you have no doubt discovered, the vent port in the sender plate sits in a recessed pocket well below the fill line. In fact it sits about 2 inches below the fill line. And about 16 inches below the "real" fill line in the neck. So if you top off your fuel tank, the vent port is underwater. If you leave a little air gap, then when the tank heats, and the gas above the fuel expands...it pushes fuel out the vent, and fills your charcoal can with fuel.

The vent location was engineered for a flat top tank, or fuel cell where the vent port is at the top of the tank. It was never designed to sit in a submerged pocket.

it won’t work.
I don’t have time to reply right now, but will later. Take a look at where the vent port is on that tank, and you will see that it is submerged when the tank is full.

It’s a bad design, and you have to change it. 50% of the people run vented caps. 25% run a different vent, and the other 25% full their charcoal cans with gasoline. Or complain about fuel odor. Or never run more than 3/4 full. Or spend all their time at swap meets looking for “the other cap”

I would type more, but I have to go modify the vent on my brand new 23 gallon fuel tank…

The fact that the vent inlet is that far below the top of the tank, and the implications of that, is obvious now that you say it, but I didn’t even think about it before I installed mine a couple weeks ago. How are you modifying it?

 

[Jaybr]

So now I'm the expert?

The answer is "no" it won't work. The M1A1 stainless tank is a work of art. It is the best made fuel tank for a Bronco that you can buy with money. I have purchased and installed several. The guy that designed the tank vent needs to be taken out behind the shed and beaten with a stick.

As you have no doubt discovered, the vent port in the sender plate sits in a recessed pocket well below the fill line. In fact it sits about 2 inches below the fill line. And about 16 inches below the "real" fill line in the neck. So if you top off your fuel tank, the vent port is underwater. If you leave a little air gap, then when the tank heats, and the gas above the fuel expands...it pushes fuel out the vent, and fills your charcoal can with fuel.

The vent location was engineered for a flat top tank, or fuel cell where the vent port is at the top of the tank. It was never designed to sit in a submerged pocket.

it won’t work.
I don’t have time to reply right now, but will later. Take a look at where the vent port is on that tank, and you will see that it is submerged when the tank is full.

It’s a bad design, and you have to change it. 50% of the people run vented caps. 25% run a different vent, and the other 25% full their charcoal cans with gasoline. Or complain about fuel odor. Or never run more than 3/4 full. Or spend all their time at swap meets looking for “the other cap”

I would type more, but I have to go modify the vent on my brand new 23 gallon fuel tank…

The valve I posted has a float in it to keep fuel out of the tube. I guess if it works, the cap becomes the overflow.

I don’t know if it’s all going to fit or work yet.


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[jamesroney]

The valve I posted has a float in it to keep fuel out of the tube. I guess if it works, the cap becomes the overflow.

I don’t know if it’s all going to fit or work yet.


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Then it's not a vent anymore. And there are plenty of victims on this forum that installed a rollover vent valve without success. They are not designed to be submerged.

The problem with the cap is that if it is "Pressure-Vacuum" cap, then it won't vent.
If its "vented, anti-surge" then it will only allow air into the tank, but won't resolve pressure.
If you drill a hole in the cap, then the cap makes a great vented cap. But if you ever lay your Bronco on it's side, you are gong to dump 23 gallons of "hi-test" in the middle of the trail.

Paul @DirtDonk has dealt with this plenty.

@neilvonarb , I just add a Rollover vent valve mounted to the top of the fill neck. That giant 5/8 diameter vent hose at the very top of the tank is very effective as a vent. I can send some pics tomorrow after I install mine.

 

[El Kabong]

You mentioned replacing rubber fuel lines. Just to double check, where did those come from? Are they designed to handle fuel? If not, I wonder if they could be the cause of the black residue.

You might also try bypassing the charcoal canister temporarily. Maybe run a temp vent hose to a high location, loop it back down into a can on the ground while it's parked. Use a tee open to the atmosphere at the top of the loop to break the siphon if the fuel starts down the the other side of the loop. Probably with a little stand pipe on the open side of the tee. The catch can would show how much fuel is being forced out. Having the charcoal can out of the system would help sort out if the black residue is coming from the charcoal. But that might take awhile if charcoal is already in the fuel.

All of that is for temporary testing, trying to hunt down an elusive problem, not a permanent fix. And will likely leave you with a fuel smell in the air.

I do a lot of plumbing on home remodels. We're into double checking territory here, so please ignore me if you've already got this stuff sorted out. Remember the old saying "water seeks its own level". That applies to any liquid. If you fill your tank so high that it fills the filler neck, it also fills anything lower than the height of the fuel in the neck. Including the charcoal canister if its below the neck. Unless the rollover valve completey blocks it. Its why they recommend to never fill the neck.

Occasionally in a house I install a filter or aerator that contains charcoal. Those always have to be flushed thru thoroughly to get past the gray/black water that comes out at first. With an automotive charcoal cannister, I wonder, since the fuel doesn't flow thru it in one direction, but instead would fill it, then return back the way it came, would it ever completely flush that residue out?

 

[jamesroney]

The fact that the vent inlet is that far below the top of the tank, and the implications of that, is obvious now that you say it, but I didn’t even think about it before I installed mine a couple weeks ago. How are you modifying it?

Here's a pic... The best thing that ever happened to that submerged vent port is a pipe plug.

 

[neilvonarb]

Here's a pic... The best thing that ever happened to that submerged vent port is a pipe plug.

So it vents to itself? What kind of gas cap will you use?

 

[jamesroney]

So it vents to itself? What kind of gas cap will you use?

No, that vent port attaches to a roll-over vent valve mounted high in the rear quarter.

I use a pressure-vacuum cap. I wanted to be able to lean the Bronco over on the trail without fuel spilling out.

 

[JKH67302]

I had the same issues with my M1A1 and it eventually flooded a charcoal canister. The vent is too low as jamesroney mentions. I copied his idea (thanks jamesroney!), I used a weldable barb from jegs and placed the port on top of the fuel neck (high as i could get it and still service the hose). I then ran my vent line from there too my stock style (delorean) 76-77 roll over valve, and then on to the evap canister. I use the later style fuel cap as well. Problem solved and no issues on trails either.

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[Bronco_007]

I had the same issues with my M1A1 and it eventually flooded a charcoal canister. The vent is too low as jamesroney mentions. I copied his idea (thanks jamesroney!), I used a weldable barb from jegs and placed the port on top of the fuel neck (high as i could get it and still service the hose). I then ran my vent line from there too my stock style (delorean) 76-77 roll over valve, and then on to the evap canister. I use the later style fuel cap as well. Problem solved and no issues on trails either.

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Where did you mount the roll over valve? Mine is same type (DeLorean) as yours. I just mounted mine and am second guessing the location…

 

[Jaybr]

I ended up putting one of these in mine. Not quite as good as moving it higher but it will keep fuel out of the line and vent fine unless the tank is completely full.

https://www.summitracing.com/parts/tnk-vv


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[WPS 73 Bronco]

Bringing this tread back to life. I too have the M1A1 tank, and I plugged the vent on the tank. Now I'm trying to figure out my game plan for tank venting.

Why can't the filler vent be routed to the evap canister on my 73 Bronco? My thought was to cap the metal tube on the filler tube. Then I would connect the filler tube vent connection
coming from the tank as the connection to the evap system. I'd put in a similar check valve in the line to prevent gas passing that valve.

 

[Oldtimer]

Why can't the filler vent be routed to the evap canister on my 73 Bronco? My thought was to cap the metal tube on the filler tube.

As long as you never plan on filling your tank in California.
Filler nozzle seals to filler neck, and displaced air won't be able to vent thru canister.