Next project weekend - NWMP Aux tank

[corax]

Look what I found on Ebay :jump:

NWMP Aux Fuel Tank '88 4Runner - (*edit* pic = results after a thorough wire brushing and POR treatment)

I've been looking for a used one for quite a while, I just couldn't justify the $600 price tag on a new one. A little bit of rust work with the cup brush and some leftover POR with a layer of truck bed coating & I should be good to go. It supposedly doesn't have any leaks, but if it does I could always weld some sheet over it (tank cleaned and filled with water of course)

This is a gravity feed system & the way it's supposed to be installed is with a tap into the main tank drain on the bottom. Problem with this is I don't like the idea of having something hang even lower off the main tank, especially something that could drain all my fuel if it gets hit hard enough. I also don't want it draining into the main tank all the time. So my thought is to put a shut valve on it (elec or manual) and have the aux tank drain into the filler neck vent tube for the main tank. My other option is to buy a cheap fuel pump to pump the aux tank into the main, but I'd like to avoid this as it takes the simplicity out of it. Does anyone have any other ideas?

 

[corax]

NWMP aux tank install

15 months and I finally got tired of moving it around to different locations, so I decided to install it today. It's supposed to be a gravity feed system with a hose running into a fitting where the main tank drain plug is on the bottom. Problem with this is I don't like the idea of having something hang even lower off the main tank, especially a brass fitting that could drain all my fuel if it gets hit hard enough.

So I thought of putting a shut valve on it (elec or manual) and have the aux tank drain into the filler neck vent tube for the main tank, but the filler neck is too high and I don't want to put a hole lower than that in the side of the main tank because I'm afraid it'll leak.

My final option is an electric fuel pump, but fuel pumps can get damaged when they run dry from heat build up and I would have no way of knowing when to shut off the extra pump. I can't find anything saying they are safe for short periods of dry running and likewise nothing about how they work except that they do not use a diaphragm.

This is what I came up with, though it may be a bit over engineered it should save the pump from running dry, and if the rest of the system wiring fails a jumper wire across the load side of the relay will still turn on the fuel pump

Red: fuel lines
Dk Blue: wiring
Parts: low pressure nitrous fuel safety switch (adjustable 2-5psi), fuel pump, momentary & toggle switches, relay, slight fuel line restriction (small crimp in steel fuel line to main tank)

- the toggle switch turns on the system, but the relay won't turn on the fuel pump until there is ~3psi at the low pressure switch
- press the momentary switch to bypass the pressure switch and turn on the relay and fuel pump
- pressure builds behind the restriction and makes the pressure switch close, the momentary switch can be let go now as the relay will stay on
- when the aux tank runs dry the pressure switch opens deactivating the relay and fuel pump

if I really want to get fancy, I was thinking I could run a wire from the + side of the fuel pump back up to the switch panel through an LED and on to ground as a "fuel pump on" indicator light

Installing the tank is easy, so I'll leave out the bits about drilling holes and bolting it into place. It's the details that'll make it trouble free in the long run . . . like an exhaust heat shield so the gas doesn't start get too hot (excessive vapor/boiling)

view from the wheel well - before I fill it for the first time I'd like to replace the rubber hose with steel braided to help deter thieves from thinking it would be easy to cut the rubber hose and steal my gas - I was also thinking a steel hard line would work, but I'd have to find another fitting first

transfer pump (universal, for a carb'd car) - I used 1/4 riv-nuts to attach it to the frame rail (still need to put a fuel filter inline to pretect the pump)

a bit of protection to keep the hoses from chaffing against the frame rail, it also keeps them tied together nicely so they don't move around much

a few months ago I had to repair the main tank fuel pump bracket because the metal line on the outside finally rusted through, while I was at it I added an extra line to dump the fuel from the aux tank into the main tank, I had actually extended that fitting down to the bottom of the tank in the hopes that it would work like a siphon once fuel starts flowing (in case the pump fails/doesn't work out I could still use the aux tank w/ pump removed)

I tossed my spare tire back under there and noticed that the tank didn't affect my departure angle at all, though if I drop off an obstacle the spare will definately take the drop. If I know I'm hitting any rough trails I'll just take the spare off and toss it in the back. I am planning on making some kind of spare carrier for the rear bumper - I always liked the idea of being able to carry 2 spare tires for longer trips.

rear view

I still have to wire it up, but that'll have to wait for another day . . . the wife started giving me the hairy eyeball for working on the truck most of the day.

 

[corax]

NWMP transfer pump wired up

changed the wiring a bit from the first idea, now I have the switches working on the ground side with the relay at the passenger side rear of the engine bay

Switches installed - turn the toggle on, press the momentary switch till there's enough pressure to trigger the pressure switch, let go of the momentary and the pump runs till the toggle is switched off or the pressure in the line drops (aux tank empty) - the blue LED is wired to the transfer pump V+ wire so it is on any time the pump is running

With the extra fuel on board I should be able to get a range just shy of 600 miles normal driving
(17 gal factory tank + 14 gal aux tank) x 19mpg = 589 miles

 

[Dave Bennett]

Nice! :Wow1:

 

[HMR]

Excellent work! Looks great! THANKS for sharing!

It's supposed to be a gravity feed system with a hose running into a fitting where the main tank drain plug is on the bottom.

Would it be possible to install a fitting on top of the tank?

I've been trying to figure out a way to add an aux tank to my Tacoma. I'd like to put something like this in the bed:

...and have it gravity feed into the factory tank. I'm trying to avoid pumps/electrics to keep it as simple as possible. Seems like it should work perfectly. Am I missing something?

 

[TEJASYOTA]

Nice install!!!!

 

[corax]

I've been trying to figure out a way to add an aux tank to my Tacoma. I'd like to put something like this in the bed:

...and have it gravity feed into the factory tank. I'm trying to avoid pumps/electrics to keep it as simple as possible. Seems like it should work perfectly. Am I missing something?

Should work fine, but make sure you put a shut-off valve on it - if not, because the tank in the bed is so much higher than the stock fuel tank, fuel will be forced up through the Evaporative Emissions line into the charcoal canister (possibly from there into the engine causing it to stall)

I would think the easiest way in your case would be to have the spare tank drain into the stock filler neck vent hose - just have to stop when the main tank is empty and open the valve on the spare tank.