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going dual tank questions?

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sm1nts2escape

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Hey everybody I am new to the site so I will introduce myself My name is sherman and I have a 85 k10 that I bought this summer and am fixing it up piece by piece.My truck has one gas tank and I want to go with dual tanks and the selector valve.I understand that there are two types of selector valves that I know of one is a 6 port the other is a 3 port.What I don't know is which one I need and why.I want dual tanks because I plan on putting a bigger engine in my truck next year maybe a 454 or 500 something and would like the luxury of two tanks.do both selector valves have a 6 prong plugin?What are the differences?Thanks for your help.

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All the factory ones I've seen have 6 ports. 3 return and 3 feed. 1 to each tank and 1 to the engine. I don't know how hard it is to wire it all, I imagine you could just pull the wires from a donor truck and be set.
 
sm1nts2escape said:
Hey everybody I am new to the site so I will introduce myself My name is sherman and I have a 85 k10 that I bought this summer and am fixing it up piece by piece.My truck has one gas tank and I want to go with dual tanks and the selector valve.I understand that there are two types of selector valves that I know of one is a 6 port the other is a 3 port.What I don't know is which one I need and why.I want dual tanks because I plan on putting a bigger engine in my truck next year maybe a 454 or 500 something and would like the luxury of two tanks.do both selector valves have a 6 prong plugin?What are the differences?Thanks for your help.
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I have everything you need if you want, I might be getting something to WV so I could bring those too.
There are 2 types but I don't think the other type is 3 ports, I will check since I have both types.
 
The plug on top of the 3 port valve that is where the power hooks up right?Can someone post a couple pics of theres mounted and wired up?Thanks
 
Without being familiar with either system directly, I would guess the 3 port is for carb applications, and the 6 port would be for a fuel injection system, where a return line is needed.
 
3/4 Ton Blazer said:
Without being familiar with either system directly, I would guess the 3 port is for carb applications, and the 6 port would be for a fuel injection system, where a return line is needed.
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Wrong.
The 6 port was the early design I had it in all my carbed trucks, the later design worked a little different and only required 3 ports for some reason, I have yet to look at my 85 to see if it is the 3 port, I know it works different than my other trucks.
 
i remember going through this with my 74 K10.. had dual tanks but the switch wouldn't work. What I remember is that the difference (electrically) with the two different systems is that system #1's control valve also controlled which tank's sending unit was actually sent up to the gage, this would be the one with the 6 prong plug. System #2 was set up so that the control valve simply controlled fuel flow, and the sending unit was controlled by the switch itself up on the dash. So you're going to find 2 different types of switches as well. system 2 is much more simple electrically as well as fuel line wise.
 
i believe "system #2" (the 3 hose type pictured above on the left) only controls the fuel input. So either the solenoid is off (fuel pump sucks from main tank) or it's on (fuel pump sucks from secondary tank). However (i could be wrong) but i believe the return line always runs back to the main tank reguardless of which tank you're taking the fuel from. Like I said, simple, and easy to wire up... just remember the dash switch will control your sending units
the other system "#2" works pretty much the same way execept it's also going to switch the return line to return to the tank you're taking the fuel from.. as well as control your sending units.

damn i'm confusing... i think i even confused myself... that's why i had to post 2 replys....
 
That makes sense the 3 port only sends return fuel back to the main tank whereas the 6 port returns back to the tank being used.How ever on the 6 port it would have one supply and one return per tankI have only seen one type of switch which I have already ordered.Now after looking at my lmc book on page 121 I see that there is a vapor line a supply line and a return line coming from the engine however I do not know if the vapor line gets connected to a tank or just the breather line on the tank.and there are some lines listed dual tank crossover line dual tank return line and vapor auxillary line.Maybe someone can shed some light on how that works per system.I looked for all of this info in my haynes manual but there isn't anything in there.Thanks for the help and the welcome.

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sm1nts2escape said:
That makes sense the 3 port only sends return fuel back to the main tank whereas the 6 port returns back to the tank being used.How ever on the 6 port it would have one supply and one return per tankI have only seen one type of switch which I have already ordered.Now after looking at my lmc book on page 121 I see that there is a vapor line a supply line and a return line coming from the engine however I do not know if the vapor line gets connected to a tank or just the breather line on the tank.and there are some lines listed dual tank crossover line dual tank return line and vapor auxillary line.Maybe someone can shed some light on how that works per system.I looked for all of this info in my haynes manual but there isn't anything in there.Thanks for the help and the welcome.
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Th vapor line has a T and collects from both tanks all the time.
The return as was said goes to the main tank which is how my 85 tanks are.
As for cross over, there are some setups that use on filler, and there is a cross over pipe to fill the second tank.
I personnaly like having a filler on each side but some prefer the look of one filler only.
 
That is what I am going for no crossover, fill from both sides.So a dual tank setup would be best with 3 port sending units and a 6 port valve.It would seem to me the 6 port vale setup would be best if I got everything correct.That way you could eliminate fuel slosh from one tank to the other?
 
sm1nts2escape said:
That is what I am going for no crossover, fill from both sides.So a dual tank setup would be best with 3 port sending units and a 6 port valve.It would seem to me the 6 port vale setup would be best if I got everything correct.That way you could eliminate fuel slosh from one tank to the other?
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Plus you know your fuel return is going back to the tank you are using, I hate it in my 85 where one tank seems to go further :confused:
 
that is the right switch for the 6 prong valve...

can't help with the fuel line / return line / vapor lines though, I can tell you what I'd do.. but i wouldn't know if its right or not
 
And....you want to haul around $1,000 of fuel each fill up or just the usual $250?:D

Happy 6 MPG
 
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