Idea about plumbing in dual fuel tanks

I have been wanting to upgrade my fuel holding capacity in my 66 CJ5. I have read though old threads, sounds easy enough to do.. however, I have a couple different ideas from what I have seen other people do. First.. I want to add a 15 gallon 1976 CJ type fuel tank. What I want to do is.. fill both tanks using only one fill neck. How can I do this ? I have thought about this and.. I think this is possible if one tank is higher than the other. Here I have drawn up a picture to show how the tanks would be plumbed together. I need to know how high the rear gas tank would be compared to the underseat one to figure out if this will work. Also, any other ideas whether if this will work or not ? I am thinking if this does work, it probably will take a while to fill up the rear tank at the pump - I'd have to wait for the gas to drain into the rear tank. Maybe a couple of minutes ?

 

I like your idea, I wonder if you could put an electric fuel pump on the line going from the under seat tank to the rear tank with a switch on the dash to turn it on. It could sporadically fill the rear tank. Keep us updated on your progress, I'd love to hear about how it goes!

 

Jonny: I am thinking a electric fuel pump may be a good idea.. if the rear tank is not lower than the underseat tank. I'd have to monitor the fuel level in the rear tank to prevent over filling it, so it wont start pumping fuel out of the vent tube. With a electric fuel pump inline of the fuel transfer line - would this electric pump act like a shut off valve when it is turned off, or would it continue to allow fuel to flow if gravity allowed it ?

 

The main problem with an idea like this ... how do you automatically fill from the front tank to the rear? If you look at the levels, I think you'll find that the rear tank level is not low enough to reliably siphon from the under-seat tank into the rear tank. And it you pumo from the under-seat tank to the rear, you have to be sure that you do not pump fuel in to higher than the normal fill level. If you overfill, you'll hae fuel coming out of the filler or vent or someplace unexpected.

I suggest you do this the conventional way, and use an electrically or manually operated valve. There's a lot of info about this on the internet - search for "dual gas tank valve." If you have a return line, I believe you have to go with the electric valve - there's no 6-way manual valve available, AFAIK.

 

Here's the electric fuel tank switch I used to go dual tanks. I'm actually using two of these. One for the fuel supply side and one for the fuel return lines. While I think you have a novel idea there, it's also kinda like re-inventing the wheel. I'd stick with the stock method of filling the tanks as I don't see any real advantage to doing it the way you are suggesting.

http://www.jamesduff.com/eb/gas_tank.html

 

I agree with Tim about doing it the conventional way-i think you're just asking for problems. It's not that big a deal to cut a hole in the back of the tub for a filler neck.
There IS a manual 6 way valve available-but I have the info at work, not here at home. I remember they're made by a marine products supply company, and they're expensive-about $150 or so.

 

Back in the old days a company made gas tanks that fit behind the rear wheels up in the fenders. They hold about 6.5 gals each.

I have a manual 3 way fuel switch. I run the saddle tanks until they are empty, then I have the gauge on the seat tank to let me know my fuel level.

I have a electric fuel pump forward of the fuel switch, so it isn't a problem when I change tanks. I don't have a return line, and I haven't seemed to miss it in the last 40 years.

I do have to fill the tanks individually. Here is a photo of the filler necks.


http://home.beyondbb.com/worman/tire.html

 

good idea
not practical to implement
even with a 1" hose connecting the tanks, you'll be there all day trying to fill it
and it you weren't using a 1" hose, 15 gal thru a 3/8" hose is even longer
Trailblazer tried that with the 25gal aux tanks in the rear of FSJ in the 70s and 80s
took forever to fill them up

 

if you ran that rear vent line up to the front tank you wouldnt haveto worry about overfilling it as it will just spew back to the top tank

 

My Commando has a manual valve between the seats to switch between the 3 tanks. Being that its a junkyard rescue, I've never had the opportunity to see how it works.

 

Hmm.. thanks for the inputs, gives me more ideas and more thinking to do.

So, sounds like it'll take way too long fill up the rear tank though the underseat tank. I took a look at electric fuel pumps.. and the fastest one I found on summitracing.com was 150 gpm(gallons per min) and this would translate into moving 15 gallons in just under 5 minutes. However this pump is over $200 a cheaper 110 gpm runs $125 and would move 15 gallons in about 8.5 minutes. So, if I were to couple this fuel pump between the tanks, I could transfer the fuel quickly. Then gravity would move fuel slowly as the motor uses the fuel(if the rear tank is lower than the underseat tank). I still need to know how high the tanks are to each other.. anyone have a setup that they can measure the height to each other ?

Also, the idea of plumbing the rear tank vent into the front tank would prevent possibly of gas spewing out is a good idea. I wonder if the gas cap vent is enough for both tanks ?

I never heard of saddle tanks, they sure do look cool ! Are these still available to buy ?

 

How about something like this?

http://www.jcwhitney.com/motor-driven-fuel-tank-selector-valve/p2005712.jcwx?filterid=j1



http://www.jcwhitney.com/fuel-tank-selector-switch/p2018980.jcwx?filterid=j1

 

I think you are mistaken with your figures.... wouldn't a 150 GPM pump move 150 gallons per minute? this would translate to 15 gallons in 6 seconds?

 

Yes. Has to be GPH. Even then, 150 GPH is 15 gal in 6 minutes. 110 GPH is 15 gal in 8.2 min.

There's no practical way to do this without some kind of sensor that tops off the rear tank until it's full. And then, you can only put 11 gal in the rear tank, at most, from one fill-up. It would take 3 fill-ups with roughly 10 min between to fill an empty system.

The Pollak valve above is a much better approach. It can be found for less through many places - check the PN on RockAuto. I believe Delco also sells the same valve under its name.

A fill neck for each tank and a 6-way valve is the way to go with this. Sometimes the conventional approach is the best approach ...

 

This is the easy way, if you look at the part numbers for all the dual tank american trucks, they used the same valve, see above. I used this valve when I added a second tank to my diesel PU. It is nice in that it switches the supply and return lines, and the sending unit too. If you don't like the look of the plastic rocker switch, you can find the right switch in a normal metal toggle style. I believe that supply lines are 3/8 and return was 5/16 on mine.

If you don't want to go with JC whitney, plug in a 76 Chevy C10 with the 454 V8 in your favorite auto parts website and look in the fuel system parts. You can find the valve, plug and switch at almost any auto parts store.

 

As far as tank heights, If you put your reserve tank in the rear and lift it so the top is snugging the bottom of the rear deck then the top of each tank will be very near the same elevation. The under-seat tank is in a drop down portion of the tub.

 

Yes, I removed the tire support. I moved the spare to the back. I wasn't too happy with it on the rear fender.

I don't have any other pictures, but could make some if you want. It's been a bit wintery here, but I hope it will warm up pretty soon.

The tanks match the curve of the rear part of the rear wheel well. There is a flange coming out the top with a couple of bolt holes. There is a lower flange on the bottom.

The only difference in the two tanks is the connection for the fuel line.

I bought the tanks in '66' or '67' from my Jeep dealer. I don't know who made them, or even how much they cost.

Quite a few of the CJ-5s in Las Cruces had them back then.

 

I have the 15 gallon rear tank and under driver seat tank. Switch between the seats. Input for fuel pump comes from the switch, and sucks from whichever tank is selected. Return line from the fuel pump only goes back to the underseat tank. Primarily use underseat tank. When it gets low, I switch to the rear, but because of the return line, the underseat tank starts to fill. Stop and go slow driving fills it pretty quick, highway harldly notice it refilling. If not paying attention and don't switch back to underseat tank, it can overflow it. Once rear tank is empty (running out of gas) switch back to underseat without a hickup. I love it, but is was there when I bought the jeep. Separate fil tubes.