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Multiple Fuel Tank Questions

DrkZide

DrkZide

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I did a search and didn't find anything that related to this.

So my 86 Longbed did NOT come with dual saddle tanks. I just have the single 20 (which I am assuming it is since it took 18 gallons yesterday when I ran it dry). I want to add the second saddle tank as well as possibly adding a suburban 40gal if I have room for it (on board air tank might be in the way).

What would the best way be of hooking all three tanks up? I know the original stock system wasn't known for it's reliability. I currently still have the mechanical fuel pump but I may have to switch to an electric pump when I drop the in the new 383 motor. I don't think they make a 3 port valve.
 
yes short bed 15-16 gal size and long bed is 20 gal size. small blazer tank is 25-26 gal and large is 31 gal. and suburban big one is 40 gal.

brackets and tank with pass side sender and bolt it up to frame . add the second fuel door and good to go. see pic's mine was single tank driver side from factory. i just added the pass side stuff . and box i got for it had 2 tank option already . holes are in the frame already . and if possible try and get brackets for pass side as if orignal the nut's will be welded on them and in correct spot. if no no biggy easy to add extra and weld them in place.

burban tank is huge and could be made to work . but i think the 31 gal deep option for a blazer fits a lot better in the trucks . make/modify a few brackets and bolt it in . possible redo of exaust tail pipe. then make a filler neck area on outside by adding the door section or make one to fill from inside the box.

and as for valves thay make electric switcher valves for 2 tanks . prob be able to find a way to wire up 2 of them to make it a 3way valve.

and if me with fuel run that long and so many tanjks mount a electric pump down on the frame next to the 2 saddle tanks area and let it push more than pull fuel.

0806121714c.jpg

0806121715b.jpg
 
There are 3 way valves, although I haven't seen electric versions in a long time. The majority are manual valves that you would mount down on the floor. My Dad had a setup like this in his Highboy with a small electric pump on the outlet side of the valve. When fuel would run dry in whichever tank he was using he would flip the pump on then switch the valve and within seconds the truck would be back under power.
 
Awesome! Now this is still going to be Carbed. Would going with 3 in tank pumps be better/worse than the single external? Are there any issues going to an electric pump vs the old mech? I know with FI there's a return line back to the tank but I don't think Carbed setups are the same. Did you use a GM valve or something aftermarket? I know GM had a 3 port and 6 port valve depending on if you needed a return line.
 
If you are talking about tank switching, AFAIK there was only ever a two tank switch used. At least on these trucks.

Personally if you can find a three position electric switch, it will be a cleaner install, as the mechanical switch will require you to run all the fuel lines over to where you can reach the switch.

If it's carbed, I wouldn't worry about electric pumps in the tanks.

As to the fuel return lines, I always suggest running them if you can. GM didn't do it for emissions reasons, they did it so heat soak and vapor lock were much less of a concern. Vapor lock is essentially eliminated with this type of setup, and it is a real problem.

Return lines I guess might be difficult, since you can't run them alltogether, otherwise you'd be refilling all the tanks while drawing from one. :)
 
So is that a yes or no on the electric pumps? My only concern is if the mech. pump has enough flow to power a Blown 383. With the return lines, I could always run the one line back to the main tank and cap off the other two. That way any tank I use will have the "excess" run back to the main tank. I may have to switch more often but I think it might save on plumbing complexity.
 
I'm sorry, can't answer you on the blown motor portion. I don't know what they require. I just know that if you can find a proven one that will flow what a blown 383 requires, and it bolts in the stock location, I'd probably use that over an electric.

Personally I'd only convert to an electric if going EFI (duh) or if there was simply no other way to run a mechanical pump. Mechanical pumps are far too simple, reliable, and inexpensive to NOT run if they are a viable option IMO.
 
So after a little bit of research, it seems like Mech. fuel pumps can actually flow a whole hell of a lot. I had no idea they made 450gph mech pumps.

I drew up a diagram I had in my head. Pretty much making the larger tank the "Primary" tank and using the saddles as "Aux" tanks. The main tank on "Valve1" and the Aux tanks on "Valve2" that feeds into the first one. I think I might go with the 6 port design as I found out that having return lines prevents against vapor lock.

What do you guys think?

Main-Aux Fuel Tanks.jpg
 
Sorry, I'm broke and not a member, can't see it. Thought of something on the return line though, depending on what you figured out.

If you use one tank as the primary for return like you mentioned, while using the other tanks, whatever is the "return" tank will overfill. That's probably not a good thing at all. Without thinking it out more, returning the fuel to just two tanks MIGHT work better?

Say you top off all your tanks. We'll call them tanks 1,2, and 3. 1 is your primary (small) tank, 2 is your big tank, and 3 is your secondary (small) tank.

If you have a return to one tank, it won't work. You will overfill the tank, the return will plug (at best) and then I'm not sure what. It may keep getting fuel to the carb, but I'm not sure fuel would circulate properly.

If you have a return going to tank 1 AND tank 2 (a tee) as fuel is attempted to be returned, since tank 2 is still full, tank 1 would be the path of least resistance and that is where the overflow would go. Then you run into the problem of how much fuel is bypassed, and how often you'd be switching tanks once you "drained" tank one. Seems like a pain to me.

Now here is a wild thought, not considering how much effort it might take. "Daisy chain" all three tanks, with all but the "last" tank using fuel caps that don't breathe (not even sure those are made or used). As you suck fuel out of tank one (the only one that feeds the fuel pump) the vacuum created would start a siphon from tank two AND tank 3. Obviously you aren't going to be drawing enough fuel to keep a strong siphon going, but theoretically I can't see why it wouldn't work. As the last tank would breathe (due to the cap), you wouldn't have to worry about the tanks being sucked shut.

That would only require one fuel line from each tank to the next tank, one line to the carb from the "first" tank in the chain, and one return line to the "primary" tank from the fuel pump. You'd have to figure out how to connect tank 2 to tank 1 though. Brazed fitting on the lower portion of tank 1 fill neck?

Just seems really simple, no extra components to fail, and far less fuel line.
 
yes there were return lines on carbed trucks.

why the hell 3 tanks??

double throw relay, switch on run the primary tank, switch off sends the signal to the tank switch letting you change from tank 2 and tank 3, done.

hit the junk yard for the parts, there are still out there.
 
So how do you run the return lines? How about the gauge sender?
 
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Another simple way is leave the stock fuel line as is and just add a cheap electric pump (on a toggle switch) to pump from the aux. tank to the main tank. When the main tank is low just hit the switch to transfer fuel from the aux. tank to the main tank.
 
Do you need a return line for each tank??? my truck does not have one.

as for the sender well, the dual tank switch has the wiring for the sender of each tank covering 2 of them for the 3rd one you will have to get creative with wiring.

just throwing out ideas here.
 
i say stock mechanical pump is fine. the issue here is plumbing and wiring. i say it can be done, but once more why 3 tanks?

Manual switch 2 of the aux tanks.
 
Doesn't hurt to brainstorm. I just liked to think my idea was pretty simple. Well, at least for three tanks. :)

Even the factory dual tank setup is a mess when you get down to it.

I agree three tanks seems excessive, who wants to see a bill for what, 60+ gallons? And the time to fill that up? Even the 30 gallon K5 tank takes seemingly forever on some pumps. (Says the guy who has a 100 gallon tank setup in a trailer so he doesn't have to travel to refuel during hunting season.)

Fuel return is a very real solution to a very real problem, even in the mild climate up here my Dad's stock 454 would vapor lock with no return. Insulating and moving the fuel lines didn't fix it, nor did an electric pump.
 
3 tanks for extended range. I'm hoping to be able to make the Alaska trip one of these years. There were two types of valves that came from GM. A 3 port and a 6 port valve, the 6 port including the return lines. I'm going to have three separate fuel gauges for each tank so the wiring would only be for the actual operation of each tank. I am going to try my hardest to stick with the mechanical as the whole them behind this build is "minimal electronics".

I'm interested in that double throw relay idea. It might be more reliable than another switch.
 
6 port didnt get you 3 tanks.

got you emmisions era send/return/vapor line hence 3 ports x2 = 6

my 2 trucks i have with 2 tanks and tbi motor i run extra carb tank and sender unit. then just use electric pump to transfer over to primary tank .
 
I don't recall ever saying the 6 ports got three tanks lol I do remember saying the 6 ports were inclusive of the return lines as the 3 were not. I might go hit up some junk yards for the other 20gal saddle and a 40gal and the Blazer 31 gal just to see which one fits better. I still need to mock up the new air tank for the OBA.
 
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