Need help with duel tank set up 82 c20 (2024)

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  • Jan 31, 2022
  • #1

K

Kjs1111

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Kyle
Truck Year
1982
Truck Model
C20
Engine Size
350 5.7 V8

Hello,

Looking for help for a fuel line diagram for dual tank set up. I decided to do a "Covid Project" and do a frame off restoration on my 1982 C20. I was able to get a 8ft bed in great shape but it is set up for dual tanks.. It would drive me crazy to have a fuel door that leads to nowhere so might as well set up as dual. I have my tanks and fuel lines but am confused on how to set it up. I want to use my mechanical fuel pump on my 350 v8 5.7l. It has two outlets (Main and return?) and one feeding direct to carb..

My questions are:
1. Sending units.. 2 outlet or 3 outlet for each side ?
2. No emissions with this old of vehicle here if it's 3 outlet can I just cap off vapor lines / run lines towards back put filter on each vapor line on both sides to prevent crap from getting in?
3. Fuel selector value - 3 port or 6? This is where I get lost of how it all gets connected. I was told I could do a 3 port with out return lines? Not sure how that would work.

If someone who has done this before could you please draw out how it should go and post it. I cannot find anything online regarding this anywhere.

I tried to draw out ideas below.
Labeled and color coded for vapor, main, and return

Thank you all !

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  • Jan 31, 2022
  • #2

75gmck25

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K25 Camper Special TH350 NP203
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5.7

- If your truck originally had dual tanks with a return line there will be 3 metal lines running along the frame rail from the tank up to the frame rail area near the fuel pump. Fuel feed and return connect to a 3 port fuel pump, and the return line runs to the canister. There will also be 3 metal lines running across the truck between the tanks. There are a lot of short rubber lines connecting it all!

- All sending units I’ve seen lately have a vapor line fitting, so the third port is for the return line. I strongly suggest using a return line, since it helps avoid vapor lock in hot weather.

- if you already have a vapor canister and lines, I would just continue to use it. Why reinvent the wheel to get rid of a passive emissions device that hurts nothing. Another simple option would be to switch to vented gas caps.

- 3 port solenoid is for a no-return system and 6 port is for a system with a return line. Try to match your dash switch up with the type of solenoid, since GM changed the setup a couple of times. Some dash switches are simple DPDT switches, while others are momentary-on switches. The momentary-on are marked with a logo like “push and hold”. Old solenoids (like my ‘75) had a single power terminal, while newer ones have a 6 wire plug. The single terminal 6 port Pollack valves are no longer available, but a couple folks have posted a wiring diagram for using the newer solenoids on an old vehicle.

  • Jan 31, 2022
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Kjs1111

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This truck had a single tank when I bought it yet had the fuel tank switch in cab. I'm starting from scratch on wiring so I can choose to make it however. I get what you are saying about running the lines and connecting them over but they would a 3 port value switch not work then ? Seems like it will only work with a 6 port and if I get vented gas caps I can cap off unused ports too ?

  • Jan 31, 2022
  • #4

75gmck25

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With vented gas caps you could cap off the vent lines.

It sounds like they might have just pulled the 2nd tank. Have you checked to see if the crossover lines are still mounted? Original had a set of metal lines, but you can also run rubber hose. You might also find the solenoid still mounted over on the passenger side frame rail under the truck.

The wiring from the dash switch probably runs through the firewall and then down the driver’s side frame rail. Is it still there?

  • Feb 1, 2022
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Kjs1111

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No I stripped everything before I got frame blasted it was never there. I think I can get this figured out now. Thank you for the help

  • Feb 1, 2022
  • #6

C10MixMaster

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This should get you in the right direction. Just omit the wiring for the electric fuel pumps , The line marked supply / return to engine would be the lines to / from the mechanical fuel pump. The vent lines (not shown here) from the tanks "T" together and connect to the vapor canister, the gas caps should be non vented when using the vapor canister.

  • Feb 1, 2022
  • #7

AKguy

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And, if you get the return lines reversed on the valve, you will know soon enough while your full tank pukes fuel all over while running on the other! Don’t ask how I know.

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Need help with duel tank set up 82 c20 (2024)

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