An on-demand reserve fuel supply for your jeep

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Topic author
4bz
Posts: 32
Joined: Wed Mar 08, 2017 12:15 pm

An on-demand reserve fuel supply for your jeep

Post by 4bz »

I added a reserve fuel supply to my 77 cherokee by installing a tank in line between the
fuel filter and the main fuel tank. The installation required a small tank (I used a 3 gallon tank), replacement
of the rubber hose that connects the fuel return line to the main tank, the addition of a fuel tank selector switch,
and fabrication of some steel lines to connect the new tank.

The installation did not require cutting of any body panels for a filler neck, cutting of the
main tank filler hose, or installation of a separate vent line. I installed the tank without a sending unit, so
there was no gauge to install or wire.

The reserve tank is filled by fuel running through the return line to the main tank. It takes about
10 minutes with the engine running to transfer enough fuel to fill the reserve tank. When the reserve tank
is full, the overflow continues flowing and goes to the main tank, just as it does in the stock setup. Venting of the reserve
tank is through the overflow line to the main tank, and fuel in the reserve tank is constantly being refreshed,
even if you do not use the reserve fuel supply.

Access to the reserve fuel supply is through a fuel selector valve (electric or manual - I used an electric
valve for more flexibility in locating the valve). If you need more fuel because the main tank is empty, flip
a switch and you have another 30-40 miles of driving range.

My cherokee has the optional dealer installed spare tire carrier inside the cargo area, so I used some of the
space under the cargo floor for locating the reserve fuel tank. The tank can be installed where ever there is
room under the vehicle.


The component costs:

3-gallon stainless steel air compressor tank - $60 (purchased from Ebay)
12-volt electric fuel tank selector switch - $50 (purchased from Ebay)
5/16 and 1/4 inch rubber fuel hose - $6
1/4 and 5/16 npt fuel hose fittings - $15
a bag full of small hose clamps - $5
3 pieces of steel fuel line - $0 (salvaged from a parts vehicle)
12 inches of 1/4 inch copper tubing - $0 (leftover from a past project)

I can provide more details if anyone has an interest.

RamJetFSJ
Posts: 431
Joined: Fri Mar 22, 2013 12:36 pm
Location: Carpinteria, CA

Re: An on-demand reserve fuel supply for your jeep

Post by RamJetFSJ »

I like it. Great idea!
80 Wag in 73 attire, Ram Jet 350 power
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jpswapmohn
Posts: 656
Joined: Sun Mar 02, 2014 6:08 pm
Location: CO

Re: An on-demand reserve fuel supply for your jeep

Post by jpswapmohn »

I am picturing this in my head, which is probably incorrect.
1. There is no pump to move the reserve fuel into the main tank for use when you run empty on the main tank? When you flip the selector switch, how does the fuel from the reserve become useful? Gravity feed to the main tank?
2. You say the fuel in the reserve is constantly refreshed. So does the return fuel have to push into the reserve to push fuel that is in the tank out and onward into the main under normal operation? Does this cause backpressure issues on the return line from and up into the engine/fuel pump?
3. Is an air compressor tank ok for fuel? I know the trike folks use kegs and such, so i would imagine that it is, but thought I would ask while i am at it.

I am pretty sure I am picturing it incorrectly, but it is a pretty good idea. With all the room back there, you could use a larger tank than 3 gallons, but I understand your intent. My fuel tank is where the spare used to be, but this could be an option along one of the frame rails...I hate only having a 19gal tank!
One day I will wake up and realize that my jeep is complete...one day, I just know it.
88Wag, LT1/4L60E/NP242, J20 axles, etc. http://imgbox.com/g/rNuIasKYrS
95YJ, STaK, D44's, SOA, ARB's, Bilstein 5150s, 35" KM2's
50 CJ3A
77 J-10 (sold)

Topic author
4bz
Posts: 32
Joined: Wed Mar 08, 2017 12:15 pm

Re: An on-demand reserve fuel supply for your jeep

Post by 4bz »

The fuel pump for the engine moves the fuel. Switching over to the reserve tank is just like having a full size auxiiary fuel tank, only smaller. Fuel feed is by vacuum pull through the fuel tank selector, just like the feed from the main tank.

Fuel running through the return line does indeed push on the fuel in the reserve tank to get back to the main tank. The largest part of the restriction is not the fuel in the reserve tank, but the extra length of return fuel line that has been added between the reserve tank and the main tank. My setup added about 10 feet to the length of the fuel return line, and the extra resistance of the longer line increased my fuel pressure slightly from about 5-3/4 psi to 6 psi. (I have a fuel pressure gauge mounted on the dash) I see more of an increase in fuel pressure on a cold day than I do from the extra fuel line.

An air compressor tank is a bit of overkill for use as a fuel tank. Air compressor tanks can have very high operating psi ratings (the one I used was rated for 250 psi). The typical fuel tank cap vents a fuel tank at something like 4 psi. The big issue with using a compressor tank is the polishing compound that was present in the tank when it was manufactured. The tank that I used was apparently poiished after welding, and polished with the threaded air ports open, so there was polishing media (grit) inside the tank. I flushed the tank with solvent before I placed it in service. Other types of tanks could also be used, but the air compressor tank was just the right size, just the right price, and made out of stainless steel so it would not corrode on the inside. It even came from the manufacturer with mounting brackets installed.

The setup could certainly be done with a tank larger than 3 gallons, but it would be a serious nuisance to use the reserve supply, refill the main tank, and then see a lot of your fuel dissappear (to refill the reserve tank) when the engine was started. I would also want a fuel gauge for a larger tank - for only 3 gallons I do not care. I still have lots of room under my vehicle for a full size fuel tank, and I may one day install one. In the meantime, the reserve tank was fast and easy, and for now it is filling my needs.
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Tatsadasayago
Posts: 3684
Joined: Thu Aug 28, 2014 2:22 pm
Location: Sacramento, CA

Re: An on-demand reserve fuel supply for your jeep

Post by Tatsadasayago »

That's a great idea!
Another good location for a tank less than 6-8" tall is between the frame rail and the rocker panels. I mounted my ViaAir on-board air tank in that spot right even with the driver's seat frame. I never scraped or dented it rock-wheeling but did munch the drain petcock.

I like the idea of having another 30-40 miles of reserve and think this is a superb idea compared to adding a large Aux tank under the rear cargo area. :)
1977 Cherokee Chief - The Blair Jeep Project III
A collection of parts flying in close formation

letank
Posts: 4009
Joined: Wed Oct 03, 2012 9:16 pm
Location: SF bay area

Re: An on-demand reserve fuel supply for your jeep

Post by letank »

Nice project, any picts of the various installed bits?
Michel
74 wag (349 Kmiles... parked, next step is a rust free body)
85 Gwag (229 Kmiles... the running test lab)

Nikkormat
Posts: 3623
Joined: Sun Jun 29, 2014 11:45 pm
Location: Salt Lake City

Re: An on-demand reserve fuel supply for your jeep

Post by Nikkormat »

Yeah, we need pictures!

The old Trailblazer aux tanks worked kind of similarly. But they were inline with the filler neck so the issue of having fuel disappear on fill up wasn't really present.
Gabe, "reformed" Jeep hoarder.

Topic author
4bz
Posts: 32
Joined: Wed Mar 08, 2017 12:15 pm

Re: An on-demand reserve fuel supply for your jeep

Post by 4bz »

I tried to post pictures, but could not get the images to successfully upload. The image sizes are 160 Kb or less. With each image, the editor downloads all but the last 2 Kb, fails, then complains that the size must be less than 768 Kb.

letank
Posts: 4009
Joined: Wed Oct 03, 2012 9:16 pm
Location: SF bay area

Re: An on-demand reserve fuel supply for your jeep

Post by letank »

4bz wrote:I tried to post pictures, but could not get the images to successfully upload. The image sizes are 160 Kb or less. With each image, the editor downloads all but the last 2 Kb, fails, then complains that the size must be less than 768 Kb.
the best way is to use a host such as (not a prefered order) Imgur, google photo, flickr

check this review

https://www.lifewire.com/free-image-hos ... es-3486329
Michel
74 wag (349 Kmiles... parked, next step is a rust free body)
85 Gwag (229 Kmiles... the running test lab)
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