Auxilary Fuel Tank

My goal here was to find the simplest way to increase the range of my truck. This should give me a total of 39 gal. (37gal. useable?) , allowing a range of 550 city/offroad and 750 mi. all highway.

What I used:

a 20 gal marine fuel tank, that will fit in the bottom of my toolbox , two #71728 male and two #71727 female Quick Connector Fuel Fittings - Chrysler/Force - Fuel Line Fittings w/ 3/8" barb, chrome-plated brass, a NAPA fuel pump (#610-1050), #CRB22057 Electric Fuel tank selector valve, two 3/8MIPx5/8"barb fittings, one 3/8"MIPx3/8"barb fitting and a 3/8"FIP tee, 1/4" barb x 1/4" FIP , 3/8"MIPx3/8"barb 90* fitting , 6' of 3/8" fuel line, 3' 5/16" fuel line , Hose clamps, Two 1"x1/2"id grommets, 12V relay, switch, wire and connectors.

FYI: the loose connector and wiring behind the blank panel (right of inst. cluster , below 4x4 switch) is for the rear wiper and hatch release switch in the Blazers.

( I need to get another one , I'm not happy with the appearance of this one. )

I picked up one at the salvage yard to use for my aux. fog lights and the aux. fuel tank. Then disassembled it and added a yellow LED for the fogs and a green LED for the pump switch as visual indicators of when they are in the "On" position (see updated photo below). So far it is a pretty easy way to wire the system. I removed the three wires that supplied the hatch release, rear wiper, and rear washer, taped them back and added my acessories. The plug has the dash light wire, a battery positive, ignition positive, and ground , that I am now using. The wiper switch is now my aux. fog light switch, and will be my aux. back-up light switch (when I install one). The hatch release activates the fuel transfer pump and selector valve relay.

Plumbing the fuel line was a real pain. Things are really tight. I had to go back and add the selector valve as a shut off, since it would siphon fuel without a shut-off. I drilled a 1" hole in the bed just off center of the left front drain hole and installed a grommet. Then drilled a 1" hole in the left bottom corner of the bed liner and the bottom corner of my toolbox. I used a grommet in the tool box too.

I mounted the fuel pump and fuel selector valve on the outside of the frame , just in front of the left rear cab mount.

The stock fuel tank vent line was easiest to cut right between the cab and bed, so that is where I installed the tee.

The system is working really well now. I can push the button and watch the fuel gauge rise in the main tank and lower in the aux. tank.

I thought it would be nice to have a fuel gauge inside, so I installed Auto Meter Gauge Works Steering column pod (part# 15007) and Auto Meter Designer Black "Streetrod Series" fuel gauge(part# 1417).

Here is the view from straight in front as I would see the instrument cluster.

I used the included green bulb filter to reduce the intensity of the gauge lighting, so it would not be a distraction at night.

The Marine tank has a mechanical gauge in the fuel cap, but having one in the cab is nice.


The grand total came to $350 (I had many of the smaller parts already)

This could be reduced significantly to less than $200 by eliminating the gauge, pod and quick connects.

Auxilary tank part "Deux"

This is the installation of a 22 gallon 1989 Isuzu Trooper tank under the rear of the truck.

I wired the fuel pump to the momentary switch on the rear wiper / washer switch , added a relay and an LED indicator light so I know it is getting power to the relay.

A digital fuel gauge will be used.The gauge can be calibrated to work with virtually any sender.The Isuzu sender operates from 16 to 120 ohms.

The install would not be so bad if it were not for the tight fit. The brackets lap over the top of the frame and come down between the spring shackles and the tank to the side mounting points on the middle lip. The frame is 35" between rails. 34" between the spring shackle bolts and the tank is 33" wide at the mounting lip. This doesn't leave much room.


I tucked it up as tight to the spare tire crossmember as possible, leaving about 1/2" space. Four 3/8" bolts hold the top of the bracket to the frame, and six 5/16" bolts attach the brackets to the tank. The brackets are not rectangular, since the tank needed to be offset slightly forward to clear the hitch.

I opted to bring the filler neck up inside the bed. I drilled a 4 1/4" hole through the bedliner and bed in the right rear corner. Primed the edges and added trim around the edge.

I used an Isuzu Trooper filler neck with a first gen S-10 mounting cup. I had to tweak the vent tube to align it with the tank and to clear the frame. The cup bolts up from the bottom using the stock hardware.

The filler tube mounting flange was trimmed and drilled to mount to the S-10 mounting cup and about a 6" long filler hose with a 45 degree angle attaches it to the tank.I didn't forget to make sure everything is properly grounded.

Now some will say , "Why in the bottom of the bed?" Well the way I use my truck it should work just fine. I didn't really want to punch a hole in the quarter panel unless I add a factory gas door. Who knows that may happen someday? The bed is easily repairable if need be.

On a side note, this tank does have a drain plug, NICE! Should the need to recover fuel arise , that will make it easy.

One of the worst parts of the install is tapping the vapor recovery system to tie the systems together. I pulled the charcoal canister and cut a tee into the line about an inch from the canister connection.

Adding the fuel line was easy. I just uncapped the unused connection on the fuel tank selector valve that was added for the first auxiliary tank. This tank is mounted below the top of the stock fuel tank , so siphoning should not be an issue.

UPDATE: 10/14/2007

Added the shield finally. I cut off the stock mounting brackets, flattened the lip on the sides and welded two pieces of angle iron with holes to match the side mounts.



This all took about 2 hours to complete. I am not sure why I put it off for two years.

The rubber fuel line from the marine tank started leaking. It was replaced with braided steel line this time.