Adding a Suburban Gas tank

Slooptin

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Ok, so here's a question I've been floating around in my head. I've got the dual 20 gallon saddle tanks on my truck and while I'm currently getting a whopping 10mpg (LS swap in the future to hopefully raise that a bit), I'd like to add some fuel capacity for the time being. I'm going to be pulling some front seats out of a wrecked 89 suburban soon to put in my truck and I've been throwing around the idea of pulling the suburban gas tank as well and using it in my truck as a sort-of transfer tank. In theory, I'll add an inline pump to transfer fuel from the burb tank to one of the 20 gallon tanks (I'll need to tap a new port into one of the 20g tanks/sending units to do this) and I'm assuming I'll have to ditch the EFI sending unit in the burb tank and use a carb sending unit since I'll only be concerned about the fuel level.

Anyone see anything in my logic that doesn't work or is missing?
 

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What about a "T" in the vent line to fill from the aux. tank?
 

Slooptin

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I'm assuming it'll have its own separate vent since its so far back
 

SirRobyn0

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Ok, so here's a question I've been floating around in my head. I've got the dual 20 gallon saddle tanks on my truck and while I'm currently getting a whopping 10mpg (LS swap in the future to hopefully raise that a bit), I'd like to add some fuel capacity for the time being. I'm going to be pulling some front seats out of a wrecked 89 suburban soon to put in my truck and I've been throwing around the idea of pulling the suburban gas tank as well and using it in my truck as a sort-of transfer tank. In theory, I'll add an inline pump to transfer fuel from the burb tank to one of the 20 gallon tanks (I'll need to tap a new port into one of the 20g tanks/sending units to do this) and I'm assuming I'll have to ditch the EFI sending unit in the burb tank and use a carb sending unit since I'll only be concerned about the fuel level.

Anyone see anything in my logic that doesn't work or is missing?
So back in the day when third tanks were added, what we'd do is added a second tank switch so for example on the main switch left would be left tank and right would be right tank, but we'd plumb the new new switch in so with the main switch on right, you'd hit the aux switch and get the back tank. That switch could also handle the gauge for that tank.

You gotta be really careful doing a transfer tank like you are describing. You have 20 gallon saddle tanks, you add a 20 gallon rear tank and you're rolling along and misjudge the level or get distracted and next thing you know your dumping gas on the ground and pumping it up the vent line and it's spilling out in the engine compartment. It's safer and easier just to plumb it in as a regular tank. I can get you a diagram and part #s for valve kits if you'd like.
 

Bextreme04

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I removed my saddle tanks and installed a 31 gallon blazer EFI tank in the back of mine. Like Rob said, you need to be really careful when adding a third tank and trying to transfer into the existing tanks. Adding another entire switching valve system is a good way to go. You can also plumb the system to use the existing electric in-tank pump to transfer to the other tanks. Personally I think it is better to just have the single tank with the electric pump in it for when you put the LS in.
 

Slooptin

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So back in the day when third tanks were added, what we'd do is added a second tank switch so for example on the main switch left would be left tank and right would be right tank, but we'd plumb the new new switch in so with the main switch on right, you'd hit the aux switch and get the back tank. That switch could also handle the gauge for that tank.

You gotta be really careful doing a transfer tank like you are describing. You have 20 gallon saddle tanks, you add a 20 gallon rear tank and you're rolling along and misjudge the level or get distracted and next thing you know your dumping gas on the ground and pumping it up the vent line and it's spilling out in the engine compartment. It's safer and easier just to plumb it in as a regular tank. I can get you a diagram and part #s for valve kits if you'd like.
ooohh part #'s would be great
 

SirRobyn0

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CheemsK1500

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I've seen this done before. One guy I saw do it put the the filler neck for the suburban tank behind the driver side tail light and used magnets and a hidden hinge to disguise it as a regular tail light. I don't remember how he plumbed it though.

Since you are thinking of an engine swap anyway, have you ever considered a 6BT or 4BT Cummins? both are more expensive than a LS, but both would consume much less fuel.
 

Slooptin

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42-308P is a common one used and includes the valve, dash switch and pigtail connector. Go to this link https://cdn.shopify.com/s/files/1/0612/8493/files/pollak_instructions_2.pdf?1231 There is a wiring diagram for 2 and 3 tank setups and even how to make it trigger electric pumps. There is more info on that page than I could type out in a few minutes. Hopefully this helps you some.
Hell yeah, thanks

I've seen this done before. One guy I saw do it put the the filler neck for the suburban tank behind the driver side tail light and used magnets and a hidden hinge to disguise it as a regular tail light. I don't remember how he plumbed it though.

Since you are thinking of an engine swap anyway, have you ever considered a 6BT or 4BT Cummins? both are more expensive than a LS, but both would consume much less fuel.
Yes, but I'd like to keep an auto trans and for my needs, diesel would be cost prohibitive. I'm also not stuck on LS, I'd consider an 8.1 or possibly even a gen 6 454/4L80e if i came across one in decent condition for cheap. MPG isn't my main concern because I know I'm not going to get diesel fuel economy with a 6.0 or 8.1, I really just want better drivability, efi/more tunability, overdrive, reliability, and a boost in power, plus a slight increase in mpg. My current 454 burns oil and could use a rebuild and I'd rather upgrade than dump money into this engine. I've had a diesel before and I have friends with diesels as well, and to me, since I'm not towing heavy, it doesn't make sense. They're fun when they work, but they can break the bank when they break.
 

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My solution was not ideal, but works if you are careful. If you have the TBI sender and pump in the burb tank, you can pump into the filler neck vent on one of your saddle tanks by adding a T. It is possible in theory to aerate the fuel this way, but hasn’t happened in my experience—that I’m aware of, at least.

I went this route because I didn’t have a tank valve that was rated for 60 psi. In my case, my truck only came with one tank from the factory and a second saddle tank was installed at some point. So the driver’s tank is my primary tank with a 60 psi pump and the passenger tank has a 10psi tbi style pump. It’s just switched 12v, so nothing fancy. I never fill the main tank past 1/2 tank (as indicated by the gauge) off the secondary tank. That avoids most potential for over filling.

I’ll see if I can find the venting diagram I drew for myself. It’s set up so that I pour fuel on the ground if I’m bone headed enough to screw up. No vent lines go anywhere near the engine bay or hot exhaust.
 

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