Dual tanks - was not expecting that

[Heatmizer]

I knew when I bought the truck a few years ago it had dual tanks but the po didn't seem to know if driver side was usable since there's no filler. There is a dual tank switch in the dash.

Was cleaning up some wiring today - I've been under the truck hundreds of times, and just today noticed the passenger side tank with the filler neck has a crossover tube running to the driver side tank.

I know this wasn't a factory option, and no idea of current state of the driver tank - sure as heck not going to flip the switch and see what gunk fills my carb.

Original plan was to remove the tanks and put a blazer tank under the bed - wood bed stepside so easy to put a filler door in the bed.

But now considering just rebuilding the whole dual tank system with the crossover. In theory more straightforward than tearing apart the bed etc to get in there, and more mileage: 1x25gal vs 2x16gal.

As for cons, I'm not concerned about saddle tanks safety - i used to drag race vws - nothing less safe than doing 100+ mph in soup can with a ta k of fuel on top of your feet.

Only con I can think is I know switches and grounds etc can be finicky sometimes but if I'm pulling everything and rebuilding then that shouldn't be a real issue.

Anyone have experience with an aftermarket dual tank crossover system?

 

[Gander]

I don’t know about aftermarket, but love having working dual tanks. I’d say fix what you’ve got, get it back to factory and it’ll work good for you.

 

[75gmck25]

Is the dash switch mounted on the metal dash near the ash tray, and is it a black rocker switch? If both answers are yes, it’s probably a factory switch. Any other type of switch is probably aftermarket, which usually means a dealer-installed auxiliary tank.

 

[Heatmizer]

Yup it's factory switch, factory valve underneath etc. I know the po's father did a bunch of work on it in 2010, so I expect he added the tank and crossover.

 

[Radiohead]

It's not hard. I went with the Standard brand kit. A little plumbing in, with new rubber, probably modify the mounting area to accommodate the new unit a smidgen, wire in the new switch and Bob's your uncle.

The hardest part for me has been deciding how I'm going to modify the original switch location to spot the new style switch. (hint: it's not the same physical shape at all, it's a modern 5/16"ish hole). I left it in the default position, plumbed to the passenger side tank since it's sending unit sort of works, until I get around to making it completely proper.

 

[goldpack]

did you want to put in a rear mounted blazer / suburban style tank.?
(as others here have typically done).

 

[jgloria223]

I have a 1975 GMC C15 step side. It came with factory dual tanks and has a factory crossover tube. The cross over tube goes to the switching valve. I am rebuilding the truck and kept the dual tanks since I am staying carbureted for now. Its actually an easy restoration and reasonable cost involved. Look at the switching valve, some are hard to find.

 

[winfred]

i've gone though my 78 3+3 dually i've replaced everything except the hard line upfront

installed tbi tanks with pumps, a late style returns too type valve, tbi pump pushes through the valve into a large bosch inline pump, then into a corvette return/filter regulator, then on to the front through a second filter just to have something just before the holley terminator x 4150 stealth to keep it clean

all switched via a relay bank from the stock later style switch, all 3 pumps are fused and relayed, the valve swaps which tbi pump feeds the main pump

 

[Grit dog]

I have a 1975 GMC C15 step side. It came with factory dual tanks and has a factory crossover tube. The cross over tube goes to the switching valve. I am rebuilding the truck and kept the dual tanks since I am staying carbureted for now. Its actually an easy restoration and reasonable cost involved. Look at the switching valve, some are hard to find.

I’m comfortable saying there was never a factory crossover on a dual tank squarebody.

 

[Grit dog]

did you want to put in a rear mounted blazer / suburban style tank.?
(as others here have typically done).

Huh?

 

[Grit dog]

I knew when I bought the truck a few years ago it had dual tanks but the po didn't seem to know if driver side was usable since there's no filler. There is a dual tank switch in the dash.

Was cleaning up some wiring today - I've been under the truck hundreds of times, and just today noticed the passenger side tank with the filler neck has a crossover tube running to the driver side tank.

I know this wasn't a factory option, and no idea of current state of the driver tank - sure as heck not going to flip the switch and see what gunk fills my carb.

Original plan was to remove the tanks and put a blazer tank under the bed - wood bed stepside so easy to put a filler door in the bed.

But now considering just rebuilding the whole dual tank system with the crossover. In theory more straightforward than tearing apart the bed etc to get in there, and more mileage: 1x25gal vs 2x16gal.

As for cons, I'm not concerned about saddle tanks safety - i used to drag race vws - nothing less safe than doing 100+ mph in soup can with a ta k of fuel on top of your feet.

Only con I can think is I know switches and grounds etc can be finicky sometimes but if I'm pulling everything and rebuilding then that shouldn't be a real issue.

Anyone have experience with an aftermarket dual tank crossover system?

This is confusing as you say it has a switch so presumably factory dual tanks, but no filler for one tank (like no hole in the bed?).
Couple things.
First, a crossover is kind of inherently unsafe. If it’s gravity it means holes in the bottom of each tank. Ever notice you never see a gas tank with an intentional hole or connection in the bottom? Expect maybe in Arkansas or any vehicle that just got the tank punched by a tweaker?
There’s a reason why and it’s pretty obvious.
A crossover out the top of the tank would require a pump and additional work and also not have a safety shutoff.
Bottom line any sort of tank crossover connection is janky and largely unsafe.
Dual tank setups are not too difficult. Several ways to do it with OE or aftermarket parts (valves switches etc).
But not really sure what configuration the truck has now to advice what would be the easiest setup.

 

[legopnuematic]

I think there might be some confusion brewing here.

I think @jgloria223 is saying they have a factory dual tank truck and there is a crossover tube for the fuel feed to the switching valve? Not a fuel filler crossover.

I take it that @Heatmizer is saying they have one fuel filler that is setup feeding both fuel tanks. Not any type of balancing/one tank feeding the other situation like GMT800 C&C with dual tanks do, the rear tank feeds and fills the front tank, shared gauge reading. Just one fill for both tanks and the normal switching valve and routing for dual tanks.

@Heatmizer pictures of the setup? The switch, valve, tanks, filler, etc.

 

[Lugnut]

That sounds a little like what I did to my truck a couple months ago when adding a second tank. Every thing is set up just like original except I didn't want to cut a hole in my bed for the passenger side filler neck, so I fabricated up this crossover tube to feed my passenger tank from the driver side. It works really well as long as the truck is sitting level or a little low on the passenger side when filling up at the station.

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[legopnuematic]

@Lugnut thank you for sharing that, I knew someone had done a dual tank-single filler setup fairly recently but was drawing a blank on who it was and my searches weren’t providing either.

 

[Frankenchevy]

There’s always the option of a filler neck/cap routed to the wheel well. Pretty accessible on my CUCV, but maybe not so much if your truck is 2wd.

I don’t think an auxiliary tank with a pump to feed your main tank is unsafe. The main tank can be plumbed to overflow back into the auxiliary tank.