Twin Fuel Tank Idea

[Phil 83K20]

I know this has been discussed previously, but I couldn’t find the thread.

The idea of having 2 tanks that are both feeding the motor, to eliminate the need for a tank switch, has been knocking around my melon for quite some time and I think I came up with a solution.

I drew a quick diagram, so skip to that if you don’t want to read out it…

Basically, I’m proposing filling from the drivers side, connecting the two with a pair of hoses, and feeding the beast from the passenger side. The addition of a check valve between the two tanks makes it so that the driver tank can flow into the passenger, but not the other way around.
It’d use a single sending unit, feed, and return setup; I personally don’t need a precise readout of the remaining fuel in the secondary tank.


Look it over and let me know if you find any problems that I overlooked.

 

[Bextreme04]

I know this has been discussed previously, but I couldn’t find the thread.

The idea of having 2 tanks that are both feeding the motor, to eliminate the need for a tank switch, has been knocking around my melon for quite some time and I think I came up with a solution.

I drew a quick diagram, so skip to that if you don’t want to read out it…

Basically, I’m proposing filling from the drivers side, connecting the two with a pair of hoses, and feeding the beast from the passenger side. The addition of a check valve between the two tanks makes it so that the driver tank can flow into the passenger, but not the other way around.
It’d use a single sending unit, feed, and return setup; I personally don’t need a precise readout of the remaining fuel in the secondary tank.


Look it over and let me know if you find any problems that I overlooked.

Well, its a solution to a problem that doesn't exist. You are going to be running an experiment and it will definitely have issues. The biggest problem I could identify when looking at something like this was that the 1" crossover line is going to be right in the way of the driveline and will be low and susceptible to damage. any leak or damage to that crossover will cause both tanks to empty. You will never know that the check valve has failed or gotten jammed until you spring such a leak and have all 30 gallon out all over your floor. The current tank designs are such that unless you have a rust through or punch through the bottom of the tank, no regular leak would allow you to lose all of your fuel.

 

[Phil 83K20]

Ah…. Yes. The driveline.
Hadn’t given it much though IN the vehicle. Mine is all sorts of disassembled…

Would still like to find a way to have better capacity without having to fill multiple tanks.

 

[75gmck25]

Many years ago the Army used a vehicle called the Gamma Goat. It was a 6 wheel, all wheel drive truck, and had once of the noisiest Diesel engines I’ve ever heard. It also had twin saddle tanks that were connected with a crossover/ balance pipe.

One of the issues I remember is that the tanks would gravity feed to each other if the vehicle was not level. There was a cap for each tank, but you always had to remove the gas cap on the uphill side and fuel up if the truck was not level. Maybe your check valve would solve that problem, but I’m not sure.

 

[Grit dog]

Your idea would work theoretically and practically save for having holes in the bottom of each tank and the aforementioned risk of losing all your fuel. Or the side that doesn’t have the check valve.
You could probably hard line it across at a cross member for protection. But a reliable leak free system would take some work.
By the time you spent the time to do it as proper and safe as possible, you could completely replace the valve, hoses, wires, switch and have a new system.
I’d just use a factory tank valve.

They’re not particularly problem prone, save for many being 30-40 years old.
If you wanted to simplify and not worry about the switching valve you could put a manual valve in the cab. Guy with a dually with an aftermarket 2nd tank showed a pic of his setup with a valve down by the floor on the seat pan. Basically like my mower with 2 tanks.
You could still switch the tank sender with the factory tank switch.
Or spend the $50 on a new selector valve which would be much easier.

 

[SirRobyn0]

Not to be another one to throw out problems I see but....

Crossover pipe, and drive line. Mentioned. Notice how no even remotely modern vehicle has a bottom exit line. and by modern I mean produced in the last 60 years or so, that's because even though a top line can possibly gravity feed some gas, with a bottom exit you spring a leak in that line and you'll put 40 gallons on the ground in a hurry if left un checked.

What if 1" is not enough flow during filling?

If you really want a 1 tank type experience you'd be better off converting a rear tank.

If you are unhappy with the reliability of the stock two tank and switch setup you'd be better off converting to aftermarket switch system such as made by Pollak or Wells. I could get you part #'s at work if you like.

Be cause there is no filter before the valves, if your tanks are not in good shape in the inside that could cause failures.

Why do you want to do this anyway you didn't say and I'm curious.

 

[Scott91370]

I say give it a try. I've thought about this as well and it does always come down to driveline. I'd like someone to be able to prove me wrong.

 

[dvdswan]

There are several ways I've seen an extra tank without a switching valve. The best one I've seen, IMO, was.. filler neck of the factory tank had a "Y" pipe installed at the filler neck to reach both tanks , depending which way you held the pump nozzle. Then the spare tank had a fuel pump installed in it which the line coming out of the tank would feed the bottom of the filler neck of the original tank to fill it.

Hope that makes sense.

 

[SquareRoot]

This outta solve all your perceived deficiencies with that pesky fuel selector switch.

GM announces electric conversion kit | electrive.com

www.electrive.com

 

[Frankenchevy]

This outta solve all your perceived deficiencies with that pesky fuel selector switch.

GM announces electric conversion kit | electrive.com

www.electrive.com

Will it catch fire like all the Chevy Bolts do?

 

[AuroraGirl]

Will it catch fire like all the Chevy Bolts do?

Only in Custom deluxe models, havent figured that part out yet but hopefully there will be one.

 

[Bextreme04]

Many years ago the Army used a vehicle called the Gamma Goat. It was a 6 wheel, all wheel drive truck, and had once of the noisiest Diesel engines I’ve ever heard. It also had twin saddle tanks that were connected with a crossover/ balance pipe.

One of the issues I remember is that the tanks would gravity feed to each other if the vehicle was not level. There was a cap for each tank, but you always had to remove the gas cap on the uphill side and fuel up if the truck was not level. Maybe your check valve would solve that problem, but I’m not sure.

We chased a problem in an M1 Abrams where it would fill the entire bottom of the turret with Diesel fuel every time they filled the fuel tanks up(there are 4 separate tanks that hold ~500 gallons total). We chased this problem for weeks and had finally come to the conclusion that one of the bladder tanks in the front of the tank must have a hole in it. Just as we were about to go through the horrible process of replacing the bladder, we finally realized that the fuel was being filled at the back tank, and was lowering itself down only part way while the front tank stayed absolutely full. Turned out there was some kind of plastic coating that was peeling off of the rear fuel tanks and had jammed a piece of plastic in a check valve that was installed in a transfer line between the front and rear tanks. The idea is that the front tanks feed the rear tanks, and that the rear tanks feed the engine. The rear tanks sit higher than the front tanks. So once the check valve got jammed, every time they filled the rear tanks it would flow into the front tanks and overflow into the inside of the tank.

They’re not particularly problem prone, save for many being 30-40 years old.

My dual tanks setup was still all original and worked perfectly when I removed it all. 41 Years old, no issues.

I ended up removing mine to go to the single 31 Gallon EFI blazer tank. I needed the baffled tank and a fuel injection pump for future mods. It also let me go with the longer 63" rear springs by moving the spring mounts forward 4".

The 31 Gallon tank sits in there perfect and is even more out of the way than the saddle tanks, plus I was able to get rid of a bunch of extra wiring and fuel lines. Its now all hard line all the way from the tank to the mechanical pump.

 

[Grit dog]

@Bextreme04, that sounds much simpler and cleaner than saddle tanks.

 

[Disco]

Ok, late to the party here, but I just posed my own dual tank idea and saw this afterward.
I was a OTR trucker for 8.5 years and a little over a million miles. Most OTR big rigs have dual saddle tanks (my last two trucks had twin 150 gallon tanks) and do almost exactly what you suggest.
The system depends on the manufacturer and how the trucks were ordered - for instance, the PACCARs (Peterbilt and Kenworth) I drove tended to pull and return the fuel from the driver side tank, while the Freightliners usually pulled from the driver side and returned to the passenger. However, the last company I worked for was out of Wisconsin and ordered their trucks with an “arctic package” fuel system that, among other things, pulled from both tanks and returned to both tanks simultaneously (the idea was it would keep fuel moving and warm in both tanks so the diesel wouldn’t gel in sub freezing weather).
There is a crossfeed system between these tanks to even out the fuel level. And I believe it was one or two large diameter fuel lines located about 1/3-1/4 the way up from the bottom (round tanks), and these lines would snake up and over the driveshaft following frame cross members. Different fuel levels in the tanks would cause a pressure differential, and gravity would force the fuel from the tank with more fuel to the tank with less, even arching over the driveline, until pressure was equalized.
Yes, if you park on an uneven surface, fuel will flow to the downhill tank, which sucks if you are low on fuel and shift the fuel to the non-feed tank.
Also, realize that there are two fuel gauges (or a single gauge with two needles) to tell you each tank’s level, and that truckers still have to fill each tank separately as the crossfeed is not fast enough to transfer fuel from one tank to the other as you fill it.

Will this system work on a Squarebody? Dunno. In theory, yes. But GM was making class 6, 7, and 8 heavy duty trucks in the 60s and 70s while they were designing the Squarebody, and many of those would have had dual tanks. If a heavy duty longhaul style fuel system would have worked on a light truck, I’m sure they would have at least made it an option. The know-how was there.
Then again, how many trucks came with dual tanks? As I understand from the period brochures I’ve found, only big block and Big 10 trucks came with the option, and they had a system GM was satisfied with: the selector valve and switch.

 

[Grit dog]

How is any of this easier and more reliable than just replacing the fuel valve if it quits working?
Or worst case re-wiring for a different valve if you have the discontinued one?