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NewX’er 4life
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Discussion Starter #1 (Edited)
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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 an aux tank to fit there since I wanted more range out of the Xterra without the need for filling Jerry cans. A stock tank on the Xterra has 21 gallons (78L). This setup allows me to carry an additional 19 gallons (70L). Not quite a second full tank but pretty close!

Rough outline of how low the spare sat in the rear:


View of where the spare used to be:


View of our stock filler and vent hoses for reference:



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:


Problems addressed
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 system.
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, and expensive. I figured why not just get an OEM style tank with a fuel pump made for it. The chosen tank for this project was a 19 gallon (70L) tank from a 2002 Chevy Blazer. Dimensions are 33" X 22" X 10 1/2". Example here.

2. Filling The Tanks
I've decided the simplest way is to fill both tanks at once via a splitter fitting. When filling up at a fuel station both tanks are filled at once. While it would be nice to isolate both tanks, money-wise it did not make sense for me. The auxiliary tank is located a tad higher than the OEM tank, so the OEM tank will fill up first.

Diagram:


Raw splitter (or "y") fitting:


3. Transferring Fuel
The fuel from the auxiliary tank will be transferred to the OEM tank via a pump. The Blazer OEM pump from the aux. tank will be turned on via a switch to initiate the transfer.

Here is the setup in the cab (ignore the puncture hole):


That Autometer gauge dims when the headlights are on and will flash when fuel is less than 10%. This was the only spot left to mount it that didn't have structural (often metal) bracing and such behind it and I didn't want a gauge pod on the dash. You will have to turn off the switch when the gauge is at 0% (or sooner if you like). Currently the Blazer pump takes approximately 20-30min to fully empty the auxiliary fuel into the OEM tank.

If you look above at the stock filler neck and now this image, you'll notice the 5/8" vent for the aux. tank was added:


The collar is essentially a funnel with another funnel crushed around it with the inner portion being for fuel and the outer being for the vented fumes. The hose fitting for the auxiliary tank had to be (carefully) welded to the outer portion of this collar similar to the OEM vent line. The filler neck has to be pulled to do this, and it is probably the hardest part since the metal is thin and tougher to weld. Just be aware of this.

Diagram of collar:


Here is a shot of the "y" fitting that splits the filler neck to each tank:


The fuel pump line from the auxiliary tank is plumbed into the OEM tank side of the splitter. If the OEM tank is full and auxiliary tank pump is turned on, fuel will just flow back into the auxiliary tank. The 5/8" line goes directly to the auxiliary tank vent connection. Since the auxiliary tank uses a 2" filler, a 1" to 2" step up was done.

Another angle showing the fuel pump line into the OEM tank side of the splitter:


4. Evap Line
With this setup, the evap system is untouched. The Xterra evap system uses a mechanical stop valve that only operates when the OEM tank is between 1/4 and 3/4 full. Testing on the main tank resulted in no fuel passing this stop valve when the OEM tank was filled to the top. So the good news is there is no need to do anything including plumb any evap for the auxiliary tank. You'll notice in the above images the lines were moved a bit but they were not modified.

5. Mounting the Tank
Mounting of the tank was achieved via a mounting cage and is completely bolt-on save for two welded mounting plates. The cross brace for the spare tire hoist was removed. The mounting plates were welded to the inner cross rail for the cage to bolt into. Additionally the cage bolts to the same location as the rear bumper re-using the two innermost bolts I believe.



Here is a picture of the cage in its infancy along with an aluminum skid and heat shield:


Here is how the actual tank is bolted in:



The skid can be removed separately from the cage and sits about 0.5-1" away from the tank (tank is not a perfect shape). Image:


Tank with skid installed:





Part numbers and prices (in CAD):

Fuel tank: GM18D, $201.27
Fuel module: SP414M, $396.48
Strap set for tank: ST122, $81.21
Autometer digital fuel gauge: 6310, $129.46

17hrs Labor and miscellaneous (wiring, nuts/bolts, paint, welding rods etc) $2992 CAD.

Total: ~$3800 CAD = ~$2858 USD

If someone were willing to replicate this, I'm sure it would come in under 2k USD because there would be less mark-up on parts and a lot of the testing and figuring out is essentially done.
 

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Following. Definitely jealous of this option on Landcruisers...

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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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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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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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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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The fill solution looks like it should work.

But, why connect the two tanks together? I think it would be much easier to have a switch to control which tank is active.

You'd have to merge the two fuel lines at some point and rig the fuel pumps to work off the switch, but that seems to be about it (at least in my mind).
 

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The fill solution looks like it should work.

But, why connect the two tanks together? I think it would be much easier to have a switch to control which tank is active.

You'd have to merge the two fuel lines at some point and rig the fuel pumps to work off the switch, but that seems to be about it (at least in my mind).
Back in the day dual tanks in pickups were common - and they used a dual tank fuel solenoid that split the line - 2 lines coming in - one going to the engine. Hit the button and it switched from one to the other. Not sure if this woudl work on the X but I don't see why not? Just google dual gas tank solenoid and see lots of examples.

The benefit I could see is you won't have to mess with the OEM tank at all - just add the second tank, split the lines, install the solenoid.

Subscribed. I would love to have a second tank
 

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If a pioneer does the heavy lifting for us and gets this done I am definitely putting one in too
 

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NewX’er 4life
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Discussion Starter #14
Updated with more photos in original 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.
Not trying to shut down this idea, but there are problems with gravity fed tanks. One is it is slow, it is dangerous for the evap system and you could overfill your main tank. Check out post 17 here. He had to hook up an electric valve and pump to make the gravity feed work and protect the evap system. His tank was above the main tank. Since I'll need a pump anyway, I figured why bother trying to gravity feed it? I would avoid an electric valve as well.

Back in the day dual tanks in pickups were common - and they used a dual tank fuel solenoid that split the line - 2 lines coming in - one going to the engine. Hit the button and it switched from one to the other. Not sure if this woudl work on the X but I don't see why not? Just google dual gas tank solenoid and see lots of examples.

The benefit I could see is you won't have to mess with the OEM tank at all - just add the second tank, split the lines, install the solenoid.

Subscribed. I would love to have a second tank
This was because old vehicles had a mechanical pump outside the tank, so you could just put two feeders coming from the pump to each tank, with one line out to the engine. Our fuel pumps are in the tank so this won't work. If you wanted a dual system, you might have to plumb it all the way into the main feeder line to the engine and would be more complicated (at least in my mind).
 

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NewX’er 4life
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Discussion Starter #15
Might take a look at what they have here https://www.summitracing.com/search/part-type/fuel-cells?PageSize=100&SortBy=Default&SortOrder=Ascending&tw=gas tanks&sw=Fuel Cells 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.
Looks promising, the OEM tanks might be a tad too big that I was looking at. I'll have to narrow it down to a few and see what the total cost is.
 

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/ said:
This was because old vehicles had a mechanical pump outside the tank, so you could just put two feeders coming from the pump to each tank, with one line out to the engine. Our fuel pumps are in the tank so this won't work. If you wanted a dual system, you might have to plumb it all the way into the main feeder line to the engine and would be more complicated (at least in my mind).
This is not true, as ford continued using dual tanks with fuel injection. However they did go away from them eventually, so maybe there was a reason.

However I don't think where the pump is changes anything. A normal electric fuel pump has an internal bypass, and it pumps fuel constantly. Whatever fuel the engine doesn't need is simple circulated back into the tank. Your fuel pump is on if you turn your key to run, even when the engine isn't running. So if you had a dual tank set up, I would think (I have no proof) that leaving both pumps running should be no problem, as the one not enabled through the splitter would just continually circulate fuel without using any. At least I think that would be the case - I have never looked into it that deeply.
 

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NewX’er 4life
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Discussion Starter #17
This is not true, as ford continued using dual tanks with fuel injection. However they did go away from them eventually, so maybe there was a reason.

However I don't think where the pump is changes anything. A normal electric fuel pump has an internal bypass, and it pumps fuel constantly. Whatever fuel the engine doesn't need is simple circulated back into the tank. Your fuel pump is on if you turn your key to run, even when the engine isn't running. So if you had a dual tank set up, I would think (I have no proof) that leaving both pumps running should be no problem, as the one not enabled through the splitter would just continually circulate fuel without using any. At least I think that would be the case - I have never looked into it that deeply.
There are a myriad of tanks systems that manufactures put out (like dual saddle tanks in Audi's that are connected by a line and have two pumps, one to just throw fuel into the other side) or Land cruisers with dual pumps and tanks etc.. My point is the old system with the exterior pump was easy to run two separate tanks off the same pump.

I don't think with ours it would be that easy. I'm not sure on the routing going out to engine and if messing with that portion would cause issues. If you had the aux pump turn on with the main pump, and plumbed in a return line from the main tank to the aux tank there is still the issue of getting the fuel back to the aux tank since it will be mounted higher. You would need another pump or something...my head hurts just thinking about it lol!
 

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Just be aware this will drive the DTE (distance to empty) calculations crazy as it is watching the fuel level in your main tank to calculate, and it thinks you only have ~18 gals. Your current MPG reading will probably be OK as that is being derived from the flow rate.
 

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NewX’er 4life
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Discussion Starter #20
Just be aware this will drive the DTE (distance to empty) calculations crazy as it is watching the fuel level in your main tank to calculate, and it thinks you only have ~18 gals. Your current MPG reading will probably be OK as that is being derived from the flow rate.
Should be ok, as stated the DTE is based on your current MPG and current level in the main tank. So, if my tank gets near empty and DTE says like 50 miles, and I switch on the aux pump to fill up the tank, it should recalculate the DTE as if I just filled the tank at a service station no? Keep in mind the aux pump will not be continuously replenishing the main tank, only when I turn it on. If it were to be constantly on maybe there would be an issue.
 
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