Idea for eliminating tank switch/switching solenoid on dual tank trucks

[dyeager535]

Not that I'll have to deal with this again as the truck is now gone, but had an idea when Dad was working on his fuel setup and had issues with the (hard to find/costly/multiple variety) fuel tank switching solenoid. Someone check my thought process.

Given a dual tank truck of course, no emissions inspection, working sending unit/gas gauge. We'll assume the passenger tank is primary.

Rip out the switching solenoid. Connect fuel level wire from passenger tank sending unit to fuel gauge, bypass tank switch.

Run outlet line from passenger tank to fuel pump. Run non-vented cap on passenger tank. Run hose from fuel outlet on drivers tank to vent line fitting on passenger tank. Drivers tank vented through existing vent or vented gas cap. Fill both tanks. Done.

As the passenger tank will have vacuum as fuel drops, it will start a siphon from the drivers tank to passenger tank since the only "vent" is the line from the driver tank. Fuel level would always be correct, as the two tanks will equalize. Thus, fuel gauge level will be the overall level.

Just seems like a pretty easy/cheap solution to the valves and switches that are necessarily complex to meet a variety of laws that perhaps you may not need to meet. I would expect this would be easer on carbed setups that don't use high pressure lines, but with work I'd think you could do the same with any EFI setup.

Any flaws with this idea? I don't have the time to mock it all up, but I can't see why it wouldn't work.

 

[rampage]

I think the problem would be the hose from fuel outlet on drivers tank to vent line fitting on passenger tank. The vacuum created in the passenger tank is against compressible gas fumes and not a "non-compressible" liquid. I think it wouldn't start suctioning until the gas in the passenger tank got much lower than the driver's tank. To solve that the line going into the vent on the passenger tank would need to be extended to the bottom of the tank instead of ending at the top of the tank ... if that makes sense.

Try doing a scale model of it with a couple of capped bottles and see what happens.
Maybe I'm wrong - maybe you're right.

 

[sweetk30]

if you could figure out the 88-98-00 body style trucks c&c trucks with front tank and second rear tank that would be ideal .

it work via the gauge reading on main tank .

if it gets to low it activates the separate transfer pump on the rear tank and sends it to the front tank till it reaches a specific level .

I like this setup but would need to dig in to the brain box to see if it can be adapted to our trucks easy .

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my 2wd build in the link below I am running 2 tanks and 1 is efi other is older carb . I will add a toggle switch for the level sender . then when efi tank low I will hit toggle switch to run transfer pump to fill from carb tank to efi tank . but I will add a huge red light in the dash so I don't forget its transferring and over fill / spill.

 

[diesel4me]

What about the charcoal canister and all its plumbing?...it would probably work if the tank was sealed air tight,but you cant have that and still pass a "visual" emission test...but you said non-emissions,so as long as its possible to seal up all the breathers and vents in the tank,I guess it could work...might need a check valve to keep the vacuum "flowing" only one way to prevent air from sneaking in maybe?..

Some newer one ton dump trucks I've seen have a set up that have two tanks, and one is the "main" tank with the sending unit and fuel pump to run the fuel injection,(and has no filler neck ,its plumbed in with the auxillary tank)--there is another electric fuel pump between the main and auxilluary tank ..
There is no switch on the dash to "change tanks"...
I'm not really sure how it works,I guess you fill the auxillary tank first,and the electric pump fills the main tank,and once that tank fills up,the auxillary one fills...so the main tank stays full until the auxillary is empty....the gas gauge must stay on full a long time,then drop pretty quickly when you get to using up the gas in the main tank..

 

[dyeager535]

Try doing a scale model of it with a couple of capped bottles and see what happens.
Maybe I'm wrong - maybe you're right.

Dammit I'm an idea guy, which means I have tons of projects and all competing for my time, I don't need more! lol But I do have a few containers I could re-purpose, thanks for THAT idea.

I see what you are saying. I know the tanks will build up substantial pressure (or vacuum) if the tank venting is screwed up, but without being able to measure it, that's pretty vague and not measurable easily.

Ideas for what I'd use as hoses for mockup? They'd have to be pretty small (thinwall) if I was going to use them on gatorade bottle caps and still have to make them airtight via silicone or whatever. Shrink tubing is about right but the walls aren't rigid enough. "Drivers" tank will be easy as it's not sealed, the "passenger" mockup will be easy I think, since it only really needs the inlet and outlet lines.

sweetk30, my idea behind this is really just to simplify the setup without needing a bunch of mods and extra parts. The only reason I can see that GM used such a "complex" system originally was for emissions, as they had to switch the evap system with the fuel. Although they probably made 1 tons early on without evap but dual tanks.

I was thinking the same thing with two TBI pumps, they run all the time a truck is running anyway, I'm sure one could think of a way to use the second tank to "top off" the other one, but again the electronics (which I'm not really afraid of, just seem unnecessary if can be done with no moving parts/electricity) make it a complex arrangement of sensors, wiring, pumps, etc.

 

[rampage]

Ideas for what I'd use as hoses for mockup? They'd have to be pretty small (thinwall) if I was going to use them on gatorade bottle caps and still have to make them airtight via silicone or whatever. Shrink tubing is about right but the walls aren't rigid enough. "Drivers" tank will be easy as it's not sealed, the "passenger" mockup will be easy I think, since it only really needs the inlet and outlet lines.

Any kind of vinyl tubing would work. Something like this:
http://www.homedepot.com/p/DIG-1-8-in-x-50-ft-Vinyl-Micro-Drip-Tubing-B34/100148024

And no need to use silicone. Just drill the holes slightly smaller than the tube and force it in - air and water tight.

 

[dyeager535]

Got some inbound, I'll try and remember what I was going to do with it once it shows up. lol

I'll update the post then. I would think this will be applicable to any dual tank setup as long as the tanks are on the same plane, not sure who might need it, I suppose an app where a single large tank would be more difficult to run than two small ones.

 

[dyeager535]

It works. At least based on gravity alone. Two identical bottles at same height/fill level, simulating two fuel tanks, one "sealed" the other open to atmosphere. Two hoses in the "primary" sealed bottle, inlet from secondary tank, outlet to "fuel pump".

Secondary tank is drawn empty before anything is drawn from primary. Not sure what problems, if any, might be experienced based on a return line into the primary tank, since that will be pressurized by the fuel pump. Might need/want the return into the secondary tank to make sure the primary never overflowed.

Don't see any other reasons this won't work on a truck. Lot simpler than all the wiring/lines/valve needed on the stock setup.

 

[dhcomp]

Ive been watching this, and agree that it should work in tests, and in theory.

What happens when you have an issue in reality in your truck though?

The transfer to level 2 tanks that are connected is foolproof.

But any sort of vac or pressure driven siphon is touchy.

 

[dyeager535]

What kind of issue could you have? Even if the siphon broke on the secondary tank you'd still have the primary, and the siphon would resume as soon as the secondary tank had fuel again.

No moving parts, no electricity, only thing that could possibly cause a problem would be a failure of the lines/hoses, which you'd have on any multiple tank setup.

Edit: I guess my way of looking at it, is that you've modified nothing but the routing of the fuel lines, and the emissions devices with this method.

If one liked the idea of a transfer tank better than this, you could also use air pressure to force it out of the one tank, or air pressure to start a siphon. Done that before, I know it works as well.