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Custom 22-Gallon Auxiliary Fuel Tank

This modification was completed in preparation for our 2004 Sierra Madre Mexico expedition, which required a fuel range of 320 miles, with 270 miles off-highway. There are several tank options available for the Tacoma, including a 15 gallon tank from Downey, in-bed tanks with gravity feed and others. I wanted the maximum fuel capacity possible, while retaining my bed space and having the tank fit inside of the current departure angle of the Demello rear bumper.

I decided to go full-custom and perform the modification myself to ensure the desired result and ability to repair in the field. The first step was to find a tank that had a capacity of 20 gallons or more and fit in the location of the Tacoma stock spare tire. I reviewed several options, including a Grand Cherokee tank, a Wrangler tank and others. I was fortunate to have my Isuzu Trooper sitting in my garage to take measurements from as well. The Trooper tank was a perfect fit, and would require no modifications to work in place of the spare tire. I called several automotive recyclers before finding a 2000 Trooper tank with the fuel pump still in place and the factory skid plate available. This combo cost $180 in AZ.

Overview of Installation

Once I got the tank home, I found several great features:
  1. The tank has a means for a secondary pick-up that bypasses the stock pump. This will allow the fitment of a back-up fuel pump if necessary. If you’re looking for vintage style gas pumps, check out Route 32 Auctions gas pumps.
  2. The stock pump is a great performer, and moved nearly two gallons per minute during bench testing.
  3. The tank has a drain on the bottom, making repairs and emergency fuel recovery easy.

Fuel tank before installation

I conducted flow testing, voltage loss and amperage draw tests to determine the needs for the pump. The unit is very efficient, pulling about 6 amps at 45 psi. I also tested the tank’s sending unit resistance, which read ~16 Ohm’s full, ~120 Ohm’s empty.

Tank testing

Tank testing

The next step was to remove the factory spare tire and support brackets. I did not remove the cross member. With the factory pieces removed, I was able to test several mounting configurations. My greatest effort was to ensure the maximum ground clearance while still ensuring proper fitment. I then took measurements and fabricated the required support brackets.

Tacoma spare tire underside

Tacoma spare tire removed underside

The Trooper tank has a strong lip around the midsection, which is used in the stock mounting configuration. I fabricated the brackets to use the same location and mount at the vehicle cross-member. It was also necessary for me to slightly down-bend the tank’s inlet to clear the frame and allow the filler tube to connect to the tank.

Tank installed

The next process required connection to the Tacoma’s factory fuel and expansion systems, and wiring the auxiliary tank’s fuel pump. The Trooper fuel pump is a two wire connection, and was connected to an ignition on circuit from my painless wiring fuse block. I ran the connection through a dash mounted switch with a red LED as a reminder/warning that the switch is on. It was also necessary to run the gauge wiring from the tank to the cab. There are two connections made to the Tacoma fuel system: the fuel inlet and the expansion.

Gauge wiring

With the fuel, expansion and electrical connections made, I needed to complete the mounting processes and test the system. I was lucky and everything worked great. I designed the system to not work as a switched fuel source, as that saved me the integration requirements to the stock EFI system and controls. The auxiliary system essentially works as a permanent refueling station. When the stock tank gets low, I activate the fuel switch and begin transferring fuel from the rear tank to the stock tank. It transfers fuel quickly and has proven to be perfectly reliable.

The last step required was to install the fuel neck and hoses. After much consideration, I decided to mount it through the rear quarter panel. The filler is protected by my stout Demello rear bumper and is easy to access for filling.

Demello rear bumper

Fuel neck and hoses installed

Lessons Learned and Loose Ends

Fuel Pump: I am in the process of redesigning the refueling system to be a little more fool-proof, as I am concerned about the chance of overfilling the stock tank and damaging the expansion system (or worse). I am investigating a momentary circuit that would only run the pump in 5 minute intervals, which equals about 10 gallons of fuel transferred.

Skid Plate: I have attached the factory Trooper skid plate, though I am using the tank mounts for support. For the time being, the skid plate can only work as a “bash plate” for light impacts. I need to rework the skid plate to attach separately to the frame so that the entire weight of the truck can be supported should I get high centered on the tank. Even though this vehicle is not used for “rock crawling”, there are many trails that I run which require protection.

Tank installed in Tacoma

Fuel tank installation complete rear view

Tacoma rear label


I am very happy with the results, and find the extra range to be a great asset. Often times I drive the Tacoma on extended highway trips en route to our adventures, and the ability to keep driving until you feel like stopping is a nice advantage. I also like not having to handle or store fuel cans.

The one negative of this system is that any auxiliary tank can draw questions at border crossing and military inspections. I have watched as several inspectors paused and looked closely at the tank, with a few banging against it with hammers to hear if fuel was there. Not a deterrent to the installation, but a caution…

NOTE: This article is NOT intended as an instruction for performing this modification yourself, but as a document of my installations. These steps are left intentionally vague, as working with your vehicle’s fuel supply requires an understanding of 12v and fuel systems, the vehicle’s emissions system and custom fabrication. Use this document at your own risk.
      1. Custom Expeditions West Installation
Payload Impact
      1. Empty: 52 lbs.- 1.9% max of payload
      1. Full: 206 lbs.- 15% max of payload
Installation Time
      1. Full custom install. Several weeks elapsed time including research, testing, fitment, fabrication, install and trials.
Difficulty (Easy, Moderate, Difficult)
      1. Difficult
Specialty Tools Required
      1. Electrical testing equipment, welder, bender, etc.
    1. Expeditions West 2004 Toyota Tacoma Double Cab TRD

Scott is the publisher and co-founder of Expedition Portal and Overland Journal. His travels by 4WD and adventure motorcycle span all seven continents and include three circumnavigations of the globe. His polar travels include two vehicle crossings of Antarctica and the first long-axis crossing of Greenland. He lives in Prescott, Arizona IG: @scott.a.brady Twitter: @scott_brady