Dual tank question

[Disco]

Hey all. So, I’m just curious and thought I’d spitball this here. My Big 10 has dual 16 gallon tanks and also has the factory selector switch which still works, if you can believe that. However, I’m well aware that that is a thing that will probably not last long. I don’t really want to screw around with new switches and valves that may or may not last very long, but I also want to keep the doubled fuel capacity (16 gallons of fuel would barely get this thirsty brick down my driveway, and I’d really like to drive back to the house when I check the mail…).

So here is the theory:
Shouldn’t I be able to bypass the selector valve with a T fitting and have the pump pull from both tanks simultaneously?
I understand that the switch also changes which sending unit is displaying its fuel level on the gauge, and I have a solution for that as well. I’d simply add a second fuel gauge on the dash and wire each sending unit to its own gauge.

What are your thoughts? Is this an overly complicated solution? Are there issues with this idea I don’t know to know about?
Thanks.

 

[CalSgt]

Theoretically yes, that’s how my valve failed it was pulling both tanks. Problem was didn’t pull evenly.

If one tank gets too low you will start pulling air. I had to cut the valve out and run one tank.

You could still use the switch to change what tank display on the dash though

 

[Disco]

Ah. Yep, that makes sense… had not considered the one dry tank. Ok, well I guess I won’t do that. Lol

 

[75gmck25]

I assume your truck is a ‘78?

If it has the old 3 port solenoid with one electrical terminal, they should be still available from Pollack and I would just install a new one. It’s the simplest solution.

If it has the old style 6 port solenoid with one electrical terminal, they are no longer available unless you find one on an old vehicle. However, I have seen postings on how to rewire and use the newer six port solenoid that’s has multiple (4?) electrical terminals.

Drawing off both tanks at once won’t work well, especially you have a fuel return line on your fuel pump.

 

[Disco]

I assume your truck is a ‘78?

If it has the old 3 port solenoid with one electrical terminal, they are readily available and I would just install a new one. It’s the simplest solution.
If it has the old style 6 port solenoid with one electrical terminal, they are no longer available. However, I have seen postings on how to rewire and use the newer six port solenoid that’s has multiple (4?) electrical terminals.

Drawing off both tanks at once won’t work well, especially you have a fuel return line on your fuel pump.

It is a 78, and it does not have return lines. It’s a pirate truck: “take what you can, give nothing back.”

 

[Disco]

Yeah, I guess drawing from both tanks is like that “two straws” experiment (put one straw in a glass of water, leave the other out, try to draw through both at the same time). It’s good ol’ physics and the “path of least resistance” again. It’s easier to pull air than fuel, so if one tank goes dry, I’ll run out of fuel, even though I have fuel in the other tank. Had not occurred to me. I forgot physics was a thing. Lol

 

[Grumpy]

I strongly advise you stay with the factory selector valve. It may be pricey and a pain to replace, but there has been considerable effort put in to the design of it.

Have you also considered moving up to dual tanks? I am assuming you may have a long box square. Two twenty-gallon tanks will only require a few different items. The best place to play compare is the LMC website, as the images are very clear as is the delineation.

 

[Disco]

No, she’s a six foot bed SWB. I’m stuck with my dual 16 gallon tanks - unless I add one of those in-bed auxiliary tanks, which is unnecessary. 32 gallons with these gas prices is plenty. Lol

 

[WP29P4A]

We had to replace the Pollack valve on my sons truck to get everything working properly, it was not a big deal.

One other idea, you could set it up like a single tank system, then put in a small fuel pump to move gas from the aux tank to the main. That could eliminate the P valve and needing to switch from one sender to the other for the gauge.

 

[Grit dog]

Didn’t know they made shortbed Big10s.

 

[Turbo4whl]

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.

 

[Disco]

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’m not sure how this works as a replacement for the electronic selector valve. As far as my vapor lines go, they appear to just be attached to the filler neck. Please explain.

Didn’t know they made shortbed Big10s.

I wasn’t even aware of the Big 10 sub-model before I bought this truck. But I assure you it has the F44 RPO code and a 6 foot bed.

 

[Turbo4whl]

Using an engine mounted fuel pump, that does not have a vapor return, nothing needs to be done with the vapor lines.

I installed this type valve in my truck that I added the second tank. Behind the seat, drill three holes. Two mounting holes and the selector stem hole. You can screw hose nipples into the 1/4" pipe or I used SAE adaptors and Push lock hose.

Yes, not as convenient as the dash switch, but does bypass electrical problems.

 

[CalSgt]

I’m not sure how this works as a replacement for the electronic selector valve. As far as my vapor lines go, they appear to just be attached to the filler neck. Please explain.

I wasn’t even aware of the Big 10 sub-model before I bought this truck. But I assure you it has the F44 RPO code and a 6 foot bed.

On my '80 there were two charcoal canisters under the hood. One vapor line ran on the inside of the passenger frame rail with the fuel feed line (fuel line not pictured) and brake line then ends right next to the steering box. The other vapor line ran on the outside of the drivers frame rail and ends about the front shock mount where it turns to plastic/rubber line.

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[Disco]

On my '80 there were two charcoal canisters under the hood. One vapor line ran on the inside of the passenger frame rail with the fuel feed line (fuel line not pictured) and brake line then ends right next to the steering box. The other vapor line ran on the outside of the drivers frame rail and ends about the front shock mount where it turns to plastic/rubber line.

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I just went out to the truck and looked. Sure enough, there are no lines or canisters on my frame rails. I don’t even see evidence there was ever any mounting brackets or anything. The only things near my steering box are my power steering lines from the pump to the box and the brake proportioning valve and brake lines. The only thing attached to the frame rail behind the driver side tire is the suspension. There are holes in the frame rail in the location you indicated that may have been the mounting point for the vapor line and canister, but there is no evidence that anything was ever bolted there.