Aux fuel tank idea - Tell me why this won't work

[JMacs]

So I have had this idea rolling around in my head for some time. Having some spare gas is a good idea, but I am not a fan of the RotoPax. Spending $150+ to carry an extra 2 gallons doesn’t rub my budget the right way. Jerry cans are a lot cheaper, but are still a bit awkward to strap down, find a place for, … So, I came up with this.



Bolt a 15 gallon tank into the bed of the truck. (10”d, 15”h, 23”l) Drain the fuel out the bottom to a solenoid valve. The other side of the solenoid valve goes to the fuel filler neck between the gas cap and the tank. When the main tank starts getting low, flip a switch, open the solenoid, and the fuel drains down into the main tank. You don’t have to get out of the truck. You don’t have to worry about spilling gas down the side of the truck trying to refuel. You don’t have to try and hold up a 5 gallon jerry can up with your bad shoulder.

When I fill up at the gas station now, I generally put between 16 and 18 gallons in. With a 15 gallon aux tank, if I wait till about that same point on the gas gauge, I can open the solenoid, and completely drain the aux tank without worry of the main over-filling. I picked making the connection in the fuel filler neck somewhere because I thought it might be a little easier to tap. And if I do screw something up while making the hole, the filler neck will be easier to replace than the whole tank.

Can someone tell me why this won’t work? I am a fan of the KISS theory of design (Keep It Simple, Stupid). This is about a simple as I can make it. Although the engineer in me has tried to make it much more complicated.

 

[Fenderfour]

Yeah, this is the basis for a lot of auxiliary bed tanks. I think they usually use a low-flow transfer pump so that it's more controlled. I also think there may be a law somewhere about gravity-fed fuel systems, that require the use of a transfer pump.

 

[Pacific Northwest yetti]

Itll work, with the KISS, just use a manual ball valve.

There are some DOT regs when it comes to gas and transfer tanks. That are stricter than diesel and transfer tanks.

 

[Dave in AZ]

So I have had this idea rolling around in my head for some time. Having some spare gas is a good idea, but I am not a fan of the RotoPax. Spending $150+ to carry an extra 2 gallons doesn’t rub my budget the right way. Jerry cans are a lot cheaper, but are still a bit awkward to strap down, find a place for, … So, I came up with this.



Bolt a 15 gallon tank into the bed of the truck. (10”d, 15”h, 23”l) Drain the fuel out the bottom to a solenoid valve. The other side of the solenoid valve goes to the fuel filler neck between the gas cap and the tank. When the main tank starts getting low, flip a switch, open the solenoid, and the fuel drains down into the main tank. You don’t have to get out of the truck. You don’t have to worry about spilling gas down the side of the truck trying to refuel. You don’t have to try and hold up a 5 gallon jerry can up with your bad shoulder.

When I fill up at the gas station now, I generally put between 16 and 18 gallons in. With a 15 gallon aux tank, if I wait till about that same point on the gas gauge, I can open the solenoid, and completely drain the aux tank without worry of the main over-filling. I picked making the connection in the fuel filler neck somewhere because I thought it might be a little easier to tap. And if I do screw something up while making the hole, the filler neck will be easier to replace than the whole tank.

Can someone tell me why this won’t work? I am a fan of the KISS theory of design (Keep It Simple, Stupid). This is about a simple as I can make it. Although the engineer in me has tried to make it much more complicated.
View attachment 838277

Yes, you need to research the DOT regs on this. The emissions test checks tank pressure, gas cap pressure, but that's just the one test they do to check several design regs.

 

[JMacs]

OK. so gravity feed is most likely not allowed. Apparently, if you want to push it, it may be legal. But just not recommended. I don't need to push it. With my luck, I will end up with that cranky inspector / state patrolman. I guess from a safety aspect it does make sense. Any issues, it will drain on the ground until empty.

So, maybe I go with an in-tank fuel pump. It shouldn't need a high volume / high pressure pump. As long as it is faster than the truck is drinking it.

 

[DiploStrat]

Back in the day, Hickey Enterprises sold a "Pacemaker" valve.

Consisted of a metal tube with a Rochester carburetor valve on the top and a cork on the the bottom.

You mounted it inside your fuel tank at the top and mounted a feed line from a physically higher auxiliary tank.

Fill both tanks - drive.

As the fuel level in the lower tank drops, the cork drops, and opens the carburetor valve, allowing fuel to flow into the lower tank. Cork rises, fuel flow stops, repeat.

In practice, the main tank drops to about 3/4 full and then the fuel gauge stops moving. Once the upper tank empties and the fuel gauge starts moving, it is time to look for more fuel.

Had two of them on different trucks - worked perfectly. Wouldn't be that hard to cobble up your own. Whether it would pass any inspection is, of course, another story.

 

[IdaSHO]

My 6.2 supeduty came with a 32 gallon tank, and rolling loaded with the camper just didnt give me the range I was willing to live with.
Larger "direct fit" tanks hang WAY too low, and cost a small fortune.

My solution was a second tank, mounted within the custom bed I built, giving me a total of 47 gallons.
Complete with its own fuel pump, fuel filler, and manual selector that controls flow from transfer (aux tank to main),
hose (acts as a fuel station to fuel generator or moto) or OFF
I have a switch in the cab to control the pump as well as a fuel gauge for the aux tank.
We routinely use it as a transfer tank, and do it while moving.
Typically run the main tank down to 1/2, then transfer from aux to main.

The tank is a 15 gallon Jeep CJ tank, with CJ fuel sender, tipover valve, and the breather is tied to the OEM vapor recovery system.
No CEL or errors. The CJ tank was the most square plastic tank i could find, and was very cheap.
Pump is a very inexpensive solid state pump, rated at 3-5 GPM as I recall.

Pics to follow, it is located between the wheel wells, right above the diff.

 

[Herbie]

The emissions test checks tank pressure, gas cap pressure, but that's just the one test they do to check several design regs.

This was my first thought too. Should be doable, but all the tank venting, etc. needs to be correct or any modern (post OBD-I) vehicle will start throwing codes.

 

[Pacific Northwest yetti]

Not all states require smog/emissions tests. So, unless you get flagged into a state scale for some reason, or someone really is digging. DOT now requires state troopers to be certified level,1,2 etc DOT inspectors, (to ticket, or inspect) and not all of them are. But, in states that require it….

 

[JMacs]

My first thoughts started along the "Pacemaker" route. But I wanted to leave the stock tank alone as much as possible. Aside from being expensive to replace if I screw up while modifying, getting the drill shavings out would suck as well.

IdaSHO, like the set up. The CJ pump might be the route I go with.

I am not as worried about emissions testing (we don't believe in that here in Nebraska). But I am concerned about the venting, etc so I don't get any codes. Another reason for the KISS.

I don't anything about the venting or recovery systems, other than they exist. If I pipe the aux fuel pump into the main filler neck and just vent the aux tank to the outside like the main(?) will that work? What else don't I know that I should before trying this?

 

[IdaSHO]

Our setup has two vents, like most factory tanks.

One is primary filler neck vent the other is a tank (vapor) vent that connects to OEM vapor recovery line.
I also installed a roll-over-valve on the tank (vapor) vent, so in the event of a rollover, fuel doesnt spill right into that line.

 

[DirtWhiskey]

I have a 50 gallon aux tank on my rig behind my cab in front of the camper. Ball valve, rollover valve on the tank, a breather and inline filter between tanks. No pump. Exceedingly common setup and perfectly legal in my home state of Utah. It transfers slowly without the pump. Probably at consumption rate or less. Thousands of setups like these rolling around. Kit is about $100. 90 gallons of fuel. Gas Buddy app has saved me thousands and it's paid for itself easily. Just know that once you fill the higher tank and it's in use with the ball valve open, DO NOT open up your gas cap!

 

[NatersXJ6]

the ball valve open, DO NOT open up your gas cap!

😂 I’ve had similar experiences opening Jerry Cans at altitude, high temperature, after bouncing around on a trail. I learned a few things in my first 2 gas-vapor shower incidents:

1) don’t fill them so far
2) if youre truly out of gas just relax and watch the sunset and fill up later when it cools
3) tell someone else youre having problems opening the can and let them do it

 

[NatersXJ6]

What does that entail? If I run a sealed gravity-feed hose into the current tank inlet, and install a modern cap on the new tank... would that work?

I think at a minimum, you would need to tie the vents together. The aux tank would have to work with the vehicle vent system.

However, caution, some jurisdictions have visual inspection requirements as part of emissions testing and modifications will be grounds for failure.

 

[Fenderfour]

My 6.2 supeduty came with a 32 gallon tank, and rolling loaded with the camper just didnt give me the range I was willing to live with.
Larger "direct fit" tanks hang WAY too low, and cost a small fortune.

My solution was a second tank, mounted within the custom bed I built, giving me a total of 47 gallons.
Complete with its own fuel pump, fuel filler, and manual selector that controls flow from transfer (aux tank to main),
hose (acts as a fuel station to fuel generator or moto) or OFF
I have a switch in the cab to control the pump as well as a fuel gauge for the aux tank.
We routinely use it as a transfer tank, and do it while moving.
Typically run the main tank down to 1/2, then transfer from aux to main.

The tank is a 15 gallon Jeep CJ tank, with CJ fuel sender, tipover valve, and the breather is tied to the OEM vapor recovery system.
No CEL or errors. The CJ tank was the most square plastic tank i could find, and was very cheap.
Pump is a very inexpensive solid state pump, rated at 3-5 GPM as I recall.

Pics to follow, it is located between the wheel wells, right above the diff.

I'm looking to add an aux tank to my little truck. Do you happen to have dimensions of the CJ tank you used?