Auxiliary Gas Tank: Planning - Second Generation Nissan Xterra Forums (2005+)
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post #1 of 81 (permalink) Old 08-09-2017, 01:06 AM Thread Starter
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Auxiliary Gas Tank: Planning

Intro

I've been going back and forth with a few ideas on what to do with the null space where my spare tire used to be. I've decided on trying to plan an aux tank to fit there. This is a thread to plan and get advice on the project. All opinions welcome.

Possible tank candidate:
'95 Pathfinder tank 34 3/8 X 20 3/4 X 11 3/4 (inches) ---21 Gal capacity

I know the Pathfinder fuel pump/sending unit are one piece and there are 4 wires (2 for the pump power and 2 for a gas gauge) since my friend has a 95 Pathy. I need to confirm how much room I have tomorrow if the rain ever stops.

Problems to address


1. Choosing a fuel tank
2. How to fill the auxiliary tank.
3. How to transfer fuel from the auxiliary tank to the main tank.
4. What to do with the evap fitting on the auxiliary tank.
5. Fabricating a mounting method for the tank.

1. Choosing a Fuel Tank
Most aftermarket tanks require the use of an electric fuel pump and a sending unit and you have to plumb these up yourself. Not to mention a lot of the aftermarket tanks are very square and not the right configuration, not to mention expensive. I figured why not just get an OEM style tank with a fuel pump made for it. My buddy's pathy seemed to be the right size and it has been there for 300k miles and has a skid plate available for it. The tank has the opening for a fuel pump (obviously), filler and vent lines and an evap line. Here is an example:

Here are photos showing tap measure at 12 inches, hanging from top of spare tire mount sheet metal. First is showing where the tap measure hangs off of, the uppermost ring.




I figure you can maybe go up to 16 inches in height, but keep in mind you would probably want a skid plate there and the rear end flexes. So for that reason max height should be 10-12 inches. You could fit 24" X 22" X 10" pretty comfortably in that spot (give or take a an inch or two). To fit a slightly longer/wider tank you need to cut more sheet metal out of the spare tire mount and would have to consider proximity to the exhaust.

2. Filling The Tanks
I've found this Nissan Patrol fuel filler which would be the initial start of the fill neck, the rest connected via hose. This goes for the vent lines as well. Notice the main line filler neck has two openings for fittings instead of just one (more on that later).

This is kind of what you would see when you open the gas door:


3. Transferring Fuel

The line coming out of the pathy tank will have an inline fuel filter. The line will be tied into the second opening of the main tank filler neck via the fitting. When the pump gets power via a switch, the gas will simply go down the filler neck of the main tank.

You should only activate the secondary pump when your main tank is close to empty. The aux tank gauge will most likely be delayed in its reading so it would be best to turn the pump off when your main gas gauge is at or close to the full mark (again might have slight delay). Likewise you don't want to have your aux tank pump running when the tank is empty. I haven't really found an automatic solution to this issue yet.

View of our stock filler and vent hoses:


View from inside spare tire location, evap on the left, filler hose in middle, vent on the right

Vent on the left, filler hose in the middle, evap on the right


4. Evap Line Fitting on Auxiliary Tank

I'm not really sure what to do with this fitting. Can you just cap it to keep the vacuum in the system? I've read on many forums of people just capping it. I suppose you could tap it into your existing evap line, but will this not tax the evap canister more or maybe throw a code? I've read most canisters are rated to handle 100 Gal tanks but I know ours used to have issues so not sure.

5. Mounting the Tank
In Progress...

Any knowledge/opinions or ideas on the matter are welcome. I'd rather not learn some hard lessons trying to pull this off by myself!
bluez, VMBiohazard, scoyoc and 2 others like this.


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Last edited by PhullD; 08-09-2017 at 01:33 PM. Reason: Updated
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post #2 of 81 (permalink) Old 08-09-2017, 01:08 AM
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Following. Definitely jealous of this option on Landcruisers...

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post #3 of 81 (permalink) Old 08-09-2017, 01:21 AM
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Following this for sure, I'd like the extended range. Also an excuse to get a rear tire carrier

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post #4 of 81 (permalink) Old 08-09-2017, 07:46 AM
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post #5 of 81 (permalink) Old 08-09-2017, 08:40 AM
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Might take a look at what they have here https://www.summitracing.com/search/...w=Fuel%20Cells I've used them over the years for some of the builds I've done. They have great customer service and tech support that can give you some ideas on how to best do your project.
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post #6 of 81 (permalink) Old 08-09-2017, 09:20 AM
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post #7 of 81 (permalink) Old 08-09-2017, 11:35 AM
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Run plumbing to fill the aux fuel tank. Don't use a pump. Line from bottom of aux fuel tank to a lower spot on main tank. Let gravity feed main tank from aux tank. No messing with electrical or wiring or anything? My initial thought.


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post #8 of 81 (permalink) Old 08-09-2017, 12:00 PM
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On motorcycles I've seen where they run the vent from the main tank up into the aux tank and let gravity feed gas from the aux into the main's vent. Then both tanks vent through the aux tank's vent. Of course it might not be so easy to mount the aux tank higher than the main tank on a X...
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post #9 of 81 (permalink) Old 08-09-2017, 12:11 PM
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Quote:
Originally Posted by Longboardr View Post
On motorcycles I've seen where they run the vent from the main tank up into the aux tank and let gravity feed gas from the aux into the main's vent. Then both tanks vent through the aux tank's vent. Of course it might not be so easy to mount the aux tank higher than the main tank on a X...
The whole thing doesn't have to be higher. I would be comfortable with the bottom of the aux tank coming 3/4 way down the main tank with the gravity fed line coming in at the half tank mark on the main tank. Once you see your fuel gauge start dropping below half tank, you know your aux tank is empty.


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post #10 of 81 (permalink) Old 08-09-2017, 12:12 PM
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Quote:
Originally Posted by ZheKing View Post
The whole thing doesn't have to be higher. I would be comfortable with the bottom of the aux tank coming 3/4 way down the main tank with the gravity fed line coming in at the half tank mark on the main tank. Once you see your fuel gauge start dropping below half tank, you know your aux tank is empty.
Yep, that would work.
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