Lowering the fill point to not overfill the tank- How do I do that?

[Romer]

I have a 21 Gallon Fuel tank I use as my primary. The gas station pump as you know doesn't shut off until the end of the nozzle detects fuel. I think in the Man-a-Fre design that overfills the tank. FJ40 BJ40 Fuel Tank Auxiliary 21 Gallon ManAFre 1958, 1959, 1960, 1961, 1962, 1963, 1964, 1965, 1966, 1967, 1968, 1969, 1970, 1971, 1972, 1973, 1974, 1975, 1976, 1977, 1978, 1979, 1980, 1981, 1982, 1983, 1984 - Landcruiser Parts - https://manafrelv.com/product/man-a-fre-21-gallon-fj40-auxiliary-fuel-tank/#
The internal design has the fill tube up to the top of the tank and by the time the nozzle shows full, as it has to backup into the hose, the tank is full to where the tank vent is. When under pressure, this allows fuel to travel up the Tank vent to the engine vapor equipment. I use a FJ40 Vapor Separator tied to a Charcoal canister. It only happens when I fill it till the pump shuts off. If I guess correctly and get it to a few gallons light, it doesn't happen and the fuel gauge shows full

Here is the tank Internal

The complete tank. I have capped two of these as they are the stock Fill and return connects and the tank has been modified to have an internal pump. The far left output is still used and is the Gas fill vent

The connection on the other side is the tank vent which I run to the Vapor separator and then Charcoal canister

Here is a view being installed into my 40 that shows more of what I am talking about

Then it mounted into my rig

I don't have access to the internal tank or I would drop it and add a 90 degree hose there

The tank fill hose is 2"

So my thought is some kind of a reducer to the 2" Hose at the input with a downward angle at the end of an inch or two. Not sure how I would do that though. That I am thinking would fill the hose and tell the gas pump it is full. I know it would keep filling the tank all things being equal, but thought the end being in a fuel earlier would cause the hose to fill and shut off the pump earlier

If I go to an 1/8 of a tank ( Likely more than that in actual tank) on the gauge and put in 15 gallons, I am good and the sender gauge shows full. If I fill it until the pump kicks off I end up with Fuel traveling to my Charcoal canister and likely more pressure than the tank should have.

Maybe it is a dumb idea., but came here looking for ideas

 

[Malleus]

@Romer , I think the 80s have a baffle in the fill tube to prevent this from happening. I used to religiously overfill my '76 tank and made a mess of the paint in the process. It's a problem, for sure.

BTW, I've been perusing your old posts on Pirate 4X4 (circa 2004), researching a solution to a starting problem on my (new) 1977. Fun stuff that the same problems persists over decades.

 

[h82crash]

If you choke down the fill tube, it will back up all the time and constantly be shutting off the nozzle. It doesn't matter where the end of the filler is, it could dump out at the bottom of the tank and you could still fill it up. The question would be, does the nozzle output out run the equilibrium that needs to occur? Looking at the tank, it will fill until all air is pushed out the vent and fuel starts dumping into it. Vents usually are high up on the filler tube to prevent gas from doing what you're describing.

This would be my suggestion. Cap off the bung on the tank and put one in the filler an inch or so behind the filler cap, in the upper half of the tube. Then reconnect the vent hose to the new bung. The nozzle should shut off before the fuel reaches the vent.

 

[Romer]

Thanks for the thought. If I understand what you are saying, I think my current full tube has that

 

[Romer]

I have been filling up at Murphy's to get the non ethanol mid grade unleaded

I noticed recently that Costco went to new Pumps (Fill my 200 there) and looks like they work on pressure vs detecting fuel at the tip. I wonder if changing to use this type of Gas station pump would take care of this ?

How do the new gas pumps work?
As the gas level in your tank rises, the air continues to flow - but when the gas reaches the level of the pipe, the air pressure inside the tube drops. The shutoff mechanism in the pump handle senses the change in suction and trips the nozzle off

 

[Romer]

I may have read that wrong on the gas station pump as a change. I found info on the older style that says the same thing

 

[h82crash]

Thanks for the thought. If I understand what you are saying, I think my current full tube has that

View attachment 3015689

Yes, use that for your vent. It should help your issue.

 

[Romer]

Yes, use that for your vent. It should help your issue.

Thanks. I already am using it. There are two vent ports, one for the fuel fill and the other to the Vapor system

 

[h82crash]

Thanks. I already am using it. There are two vent ports, one for the fuel fill and the other to the Vapor system

Where does the filler vent go? The filler vent still should be connected to the vapor system, correct? Plug the lower vent, that is where fuel is getting into your vapor system.

 

[Romer]

The filler vent is up high and near the fill tube. That goes to the fill tube Port.

The Tank vent is on the other side of the tank up high and goes to the vapor system

This picture best illustates their locations

 

[h82crash]

I'm just trying to help. I think we've identified the issue and I have suggested one possible solution. Put a tee in your vapor return line, aka filler vent and run your canister line to it. Can't hurt to try it.

Also, I've seen illustrations of fuel tank vents and some show a ball check called a rollover valve, like a wet/dry vacuum has, that allow vapors in the line but when fuel reaches it, it shuts off.

 

[Romer]

I'm just trying to help. I think we've identified the issue and I have suggested one possible solution. Put a tee in your vapor return line, aka filler vent and run your canister line to it. Can't hurt to try it.

Also, I've seen illustrations of fuel tank vents and some show a ball check called a rollover valve, like a wet/dry vacuum has, that allow vapors in the line but when fuel reaches it, it shuts off.

Don't get me wrong, I appreciate any help and advice. It is hard to tell that in a 2 dimensional medium. I am an engineer and like to understand the why. If I have two vents and one is going to the Vapor system and one is going to the gas fill tube, what is the difference from that if I cap one and then tee it off the other? It seems the smaller dimension of the Tee would reduce the pressure/vapor flow to the canister and to the fill tube. It is Fuel Injected so it goes under pressure and that is what causes the fuel to go up the vent line when it is all the way full. Less air and more fuel volume forces it up the vent line from the pressure. That I have known all along. I bought a spare Gas Cap and just drilled a small hole to help with venting. The thread was asking about the feasibility of what is likely a dumb idea, to lower the fill point. I know if I drop the tan k, I can likely go in through the pump hole and make a modification to the fill pipe. If I add a 90 degree hose that goes down another inch when the fuel reaches the lip of that end the pressure will change shutting off the pump. It slows down the fill of the tank while changing the pressure and fluid in the fill tube.

Between the vent, I am using an FJ40 Vapor separator, check valve and then to the Charcoal canister

I am assuming based on the replies so far that there really isn't an easy way to lower the point the gas station pump auto shut off engages. So far I have a method that works, run it down to 1/8 a tank and then put in 15 gallons. Being an engineer I wanted to make it automatic so eventually long after I am gone it doesn't become a PO item for someone else.

 

[h82crash]

I don't believe there is any difference in the way the vent would operate. The filler vent only helps reduce pressure in the fill pipe during filling to prevent fuel from backing up the pipe. Once the cap is on, it does nothing. But, if you tee into it, it could serve a dual purpose. I would use a tee that was appropriate diameter for the fill vent and a reduced branch for the vapor line.

Putting a 90 elbow on the outlet in the tank might work if pressure change shuts off the nozzle, but is that the way all nozzles work? Do you have vapor recovery nozzles there? We do not. I don't believe a small change in air pressure is shutting off the nozzles where standard, non vapor recovery nozzles are used. I can hear the fuel gurgling up the fill pipe before it shuts off. Same with filling portable gas cans. With vapor recovery nozzles, you need to pull back on the sleeve and let the pressure out or the nozzle won't dispense into a portable can.

My thoughts were that the goal was to be able to fill your tank and prevent the fuel from entering the vapor system, not just finding a way to automatically underfill your tank.

 

[lcwizard]

I have a 21 Gallon Fuel tank I use as my primary. The gas station pump as you know doesn't shut off until the end of the nozzle detects fuel. I think in the Man-a-Fre design that overfills the tank. FJ40 BJ40 Fuel Tank Auxiliary 21 Gallon ManAFre 1958, 1959, 1960, 1961, 1962, 1963, 1964, 1965, 1966, 1967, 1968, 1969, 1970, 1971, 1972, 1973, 1974, 1975, 1976, 1977, 1978, 1979, 1980, 1981, 1982, 1983, 1984 - Landcruiser Parts - https://manafrelv.com/product/man-a-fre-21-gallon-fj40-auxiliary-fuel-tank/#
The internal design has the fill tube up to the top of the tank and by the time the nozzle shows full, as it has to backup into the hose, the tank is full to where the tank vent is. When under pressure, this allows fuel to travel up the Tank vent to the engine vapor equipment. I use a FJ40 Vapor Separator tied to a Charcoal canister. It only happens when I fill it till the pump shuts off. If I guess correctly and get it to a few gallons light, it doesn't happen and the fuel gauge shows full

Here is the tank Internal
View attachment 3015627

The complete tank. I have capped two of these as they are the stock Fill and return connects and the tank has been modified to have an internal pump. The far left output is still used and is the Gas fill vent
View attachment 3015631
The connection on the other side is the tank vent which I run to the Vapor separator and then Charcoal canister
View attachment 3015632

Here is a view being installed into my 40 that shows more of what I am talking about
View attachment 3015633

Then it mounted into my rig
View attachment 3015634

I don't have access to the internal tank or I would drop it and add a 90 degree hose there

The tank fill hose is 2"

So my thought is some kind of a reducer to the 2" Hose at the input with a downward angle at the end of an inch or two. Not sure how I would do that though. That I am thinking would fill the hose and tell the gas pump it is full. I know it would keep filling the tank all things being equal, but thought the end being in a fuel earlier would cause the hose to fill and shut off the pump earlier

If I go to an 1/8 of a tank ( Likely more than that in actual tank) on the gauge and put in 15 gallons, I am good and the sender gauge shows full. If I fill it until the pump kicks off I end up with Fuel traveling to my Charcoal canister and likely more pressure than the tank should have.

Maybe it is a dumb idea., but came here looking for ideas

When the tank is "full" depends on how low the fill tube is placed inside the tank in relation to the top of the tank. The fill tube, welded inside the tank needs to protrude down far enough that the tank doesn't completely fill. There needs to be room for expansion. When I build a tank I make sure the fill tube is at least 2" below the level of the roof of the tank. When gas hits the fill tube it should trigger the venturi effect, that shuts the pump off. The pump shuts down when displaced air stops escaping
hose. The pump should shut off when fuel hits the venturi tube

 

[h82crash]

When the tank is "full" depends on how low the fill tube is placed inside the tank in relation to the top of the tank. The fill tube, welded inside the tank needs to protrude down far enough that the tank doesn't completely fill. There needs to be room for expansion. When I build a tank I make sure the fill tube is at least 2" below the level of the roof of the tank. When gas hits the fill tube it should trigger the venturi effect, that shuts the pump off. The pump shuts down when displaced air stops escaping
hose. The pump should shut off when fuel hits the venturi tube

Maybe in Kali where you have the gawd awful, accordian sleeved, vapor recovery nozzles. Most of the rest of us have these. They shut off when fuel reaches it. Now, if the output of the pump is high, then the fill tube may fill faster than equilibrium can compensate and it will back up the filler and shut down the nozzle. But a slow pump will completely fill the tank.

 

[Vandal FJ]

I have the Downey version of the tank, and I get backflow and spill over if the fuel isn't trickled in there slowly. It sucks, would love to hear anyone's opinion on that...