Dual tank question

[Disco]

My guess is if my truck had a charcoal canister (which I assume it did from the factory, mounted to the top of the inner fender beside the washer fluid reservoir), the original owner deleted it a long time ago, along with the frame mounted lines and the canister mounting bracket.

 

[RecklessWOT]

The simple mechanical fix is replace the plastic factory valve with a brass valve. If you are running a carb with no fuel return, just "T" the vapor lines together. Vapor will go to the tank that is being drained by the pump.

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Still use the dash switch to switch the gauges.

I didn't know this was even a thing people did, but was going to suggest something similar. Not exactly the same as what you're saying, but still something that involved a mechanical valve. Honestly your idea makes even more sense than mine, that's just what I would personally do if it were my truck. Dash switch should still work to display the fuel level of the tank you choose on the gauge, but it's on you to flip it manually for which tank it will suck from. A minor inconvenience that I am not above working with. For some people losing the convience might be a dealbreaker, some just can't deal with a minor inconvenience (why manual t-cases have gone away, as if it were a big deal to throw a lever rather than push a button on the dash), but for those of us who just want the damn thing to run, sounds like a good setup to me...

 

[Disco]

I get you. I am not necessarily above dealing with inconvenience. Otherwise I would have gotten something new with an automatic transmission and air conditioning. I’m just planning ahead, weighing my options, because eventually (probably sooner than later) that valve will stop switching tanks. So the question I am considering is which inconvenience do I deal with? Replacing the OE style valve? Driving around with only one tank? Plumbing a mechanical valve?

Regardless, I have an answer to my question. Tying the tanks together would be a bad idea. Thanks everyone!

 

[Dave M]

These work fine

Fuel Tank Selector Switching Valve 3 Port Dual Switch Main Aux Gas FV1 FV1T | eBay

Manufacturer Part NumberFSV3, FV1, FV1T. TypeFuel Cell Surge Tank. Vehicles with one main and one auxiliary fuel tank. Located between the fuel pump and the fuel tank. Fuel TypeDiesel. 3/8" Hose Barbs for use with 5/16" fuel lines.

www.ebay.com

If your worried being caught out, fit a new one. I have one of these in my '76, to run from the L/H tank it is energised. So I use mostly the R/h tank to avoid using the solenoid all the time. I flick it over on occassion to keep it working, or as needed, & before the fuel gets too old.

 

[SirRobyn0]

Ok guys I will try to answer the vapor canister question as best I know. It seems to very from year to year weather dual tanks got two canisters or only one. However there is no reason one canister can't handle both, there is nothing wrong with the vent lines being merged.

@Disco There were two, we really four different valves and two different switches. One type handles the gas gauge change from tank to tank on the switch and runs one wire to the valve on the frame rail. These units have issues and are prone to failure. The later systems the gauge change was handled by the valve on the frame rail and it VERY reliable as long as your tanks are clean and your pumping rust though the valve. And there there is with and without return lines. Pollak makes a kit to switch to the better valve but replaces your stock switch with a toggle switch.

 

[Royal Sierra 454]

I like the topic. My GMC short bed has dual 16 gal. tanks. Something to plan for down the road.

 

[Dave M]

Ok guys I will try to answer the vapor canister question as best I know. It seems to very from year to year weather dual tanks got two canisters or only one. However there is no reason one canister can't handle both, there is nothing wrong with the vent lines being merged.

@Disco There were two, we really four different valves and two different switches. One type handles the gas gauge change from tank to tank on the switch and runs one wire to the valve on the frame rail. These units have issues and are prone to failure. The later systems the gauge change was handled by the valve on the frame rail and it VERY reliable as long as your tanks are clean and your pumping rust though the valve. And there there is with and without return lines. Pollak makes a kit to switch to the better valve but replaces your stock switch with a toggle switch.

Can't agree, as both are prone to failure. Tthe old 3 port is either on or off, simple solenoid coil, it either shunts the valve port for L or R tank pickup. Correct, the gauge is controlled via the selector switch. Possibly the valve becomes unreliable if you only ever keep using the LH tank and are forever having the valve coil energised. Yes it may have voltage fluctuations and eventually burn out the coil, it is an electrical item. The later ones are also VERY susceptible to failure, as they use a small drive motor to wind the valve from one end to the other. It also relys on internal contacts to control the fuel gauge. The main reason for the 6 ports is to valve the return lines in conjunction with the pickup lines.

 

[SquareRoot]

Do it right and save yourself the headache. The parts are available and cheap.

 

[SirRobyn0]

Can't agree, as both are prone to failure. Tthe old 3 port is either on or off, simple solenoid coil, it either shunts the valve port for L or R tank pickup. Correct, the gauge is controlled via the selector switch. Possibly the valve becomes unreliable if you only ever keep using the LH tank and are forever having the valve coil energised. Yes it may have voltage fluctuations and eventually burn out the coil, it is an electrical item. The later ones are also VERY susceptible to failure, as they use a small drive motor to wind the valve from one end to the other. It also relys on internal contacts to control the fuel gauge. The main reason for the 6 ports is to valve the return lines in conjunction with the pickup lines.

I probably should have elaborated better in my previous post, but in the end we may have to agree to disagree on this one.

4 types of valves were used. Single wire valves were made with either 3 or 6 ports. 6 wire valves were made 3 or 6 ports.

The single wire valves had a couple of issues. One is they are solenoid with a tension spring, and seems to be less reliable than than the motor in the 6 wire valve. Next the single wire valve requires a good ground contact with the frame, if the mounting area corrodes or a guy changes the valve without cleaning it up, it won't work or won't work correctly. The 6 wire valve does not rely on frame contact for a ground. Last this doesn't really reflect reliability, but because the single wire valve handles the gauge change in the switch if the valve fails the gauge still changes so the driver is blissfully unaware that the tank hasn't changed over until it runs dry. With the 6 wire valve the if the valve fails to move the gauge won't change so the driver knows right away that there is a problem.

The single wire valves are more prone to failure, but the 6 wire valves are not infallible either. I base this information on what I see at the shop and that there are kits made to convert to the 6 wire valve and for a fresh install, but for the single wire valves there is no kit, but the valve is still available.

 

[80BrownK10]

I didn't think the single wire valves were available?

 

[SirRobyn0]

I didn't think the single wire valves were available?

Well, last time I need one at the shop they still were IIRC about a year ago. But they should be discontinued so we can convert all the single wires to the better valve! Standard Motor products PN# FV1T, is the 3 line valve, but I cannot find a PN for the one with the return line, so those maybe gone now.

Standard motor products FV-5K is the 5 line kit that work great to convert a truck over, or even for a truck with the existing 6 wire valve. It's affordable and even if I guy doesn't need a the switch it includes the pigtail.