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
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!