2nd gas tank 1971 FJ40

[Antarctica32]

The 1971 FJ40 I purchased last week (my first LC) came with a 2nd fuel tank. It's pretty big, I did the math and it comes out to around 22 gallons, depending on thickness of the steel. The fuel line (not the metal kind) goes from the tank to a joint with the line from the OEM tank. A switch to the left of the driver on the floor, right next to the seat, controls witch tank you use. The only trouble, the switch is stuck in one position, I have no clue witch tank it is stuck on (switch isn't labeled), the fuel gauge is reading just about empty, and one of the fuel lines (the one going from the 2nd tank to the joint) has a leak in it. I've never messed with this kind of thing, how would I find out if the 2nd tank has a fuel gauge sender with it? I'm not even sure if that's the right word for it. Without knowing how full the 2nd tank is, I have no clue how much fuel will come out when I replace the line. Any advice for my sticky situation? What do you think of this 2nd tank?

 

[Solace in Solitude]

Welcome to MUD!!

First off, it appears, from your pictures that you tank is welded to the frame - if so, that's gonna make it harder to drop your tank.

Regarding your sender question - if there's a sender, it would most likely be mounted on top the tank - you would need to be able to access the top of the tank to check it - he easiest way to determine whether you have a sender is to look for wires coming from the top of the tank - there would be a wire running from the sender to the gauge and a second wire to ground the sender - probably to a bolt near the tank. Ther could be a third wire... if there are no wires, there is no working sender.

My guess is that you have an oem main tank, running to the oem fuel gauge and an auxiliary tank that does not run to the oem fuel gauge...

The valve on the floor would allow you to run the aux tank dry and then switch to the main tank, with a working gauge.

But, this is all a guess...

For the switching valve...

• I would get a few buckets ready and disconnect the hose coming from the aux tank to the valve and drain the tank into the buckets (unless you are sure the aux tank and gas are clean). You can crimp the fuel line to change buckets.
• I would do the same for the main tank (again, unless you are sure the main tank and gas are clean)
• Swap in a new valve - or, if you want to share the oem fuel gauge, between tanks, install an electronic switching valve (like Pollak or others). is would require the aux tank have an oem sending unit or another sender that works at 120ohms empty and 17ohms full. I ran into issues trying to use a Centroid sender because they have changed to digital senders that no longer work with the self-regulated oem fuel gauge. Its just easier to make an oem sender work - you may have to lengthen the sender's float-shaft.
• Replace all your soft lines and blow out your hard lines - or, replace them if they are not good lines.

It would be much easier, at this point, for you to just swap in a new valve and run your non-gauged-aux-tank dry, then run your gauged-man-tank. That way you don't need to know how much gas is in your aux tank - just switch wen it's going dry - or, switch when you have reached some 'estimated mileage' threshold.

But, I would want to know both tanks are clean - it looks like it's been on there a while and it could be full of crap... dropping the aux tank may take grinding off the welds (if that's how it's mounted) or a cutting torch and you will want to be very careful using heat around a gas tank - even an empty one - I would take to to a professional to have this done and find a better way to remount it.

I would also, pull the main tank and clean it and check under it for pin holes and rust - you really want it to be clean as well.

You may want to consider re-mounting the aux tank with a skid plate and hanger system - Jim ( @Downey on MUD ) may be able to provide a solution for this. He may respond here or you can start a conversation with him here, on MUD.

hth

 

[Downey]

Only mistake Danny made is his Sept 1972-newer rig uses the 120 ohm empty/17 ohm full sender, your Sept 1972-older rig uses the older 100 ohms empty/3 ohms full sender on a 7 volt drop system. Either use a stock Sept 1972-older Toyota sender in your rear tank OR use a separate dash gauge for your rear tank, and any sender that matches that gauge. Once you decide what you want to do lemme know because I can provide complete rear tank installation/electrical/plumbing instruction manual.

 

[Antarctica32]

Thank you for your insight. Today I was able to pull out the leaking fuel line and get a new one in. The switch (I'll get a picture of it soon) is pretty stuck in one position. I used copious amounts of WD40 on it, but I can't get it to move without risking breaking it. Before I changed the fuel line and started messing with the switch, the whole thing (switch, joint where the 3 lines come together) was just covered with gunk and grime. After removing a lot of that grime, i've gotten a better look at it and it isn't in too bad shape.

The fuel gauge was reading just about empty, and with the switch stuck in the one position, I decided to run the engine until it ran out of gas. After about 5 minutes, the engine stopped, the gauge was fully on the E, and I added a few gallons to the OEM tank. After adding that, the engine started right up. So now I know that the switch is stuck on the OEM tank.


I will let you know what I decide to do going forward, I just thought I should update you. This whole 2 fuel tank thing isn't exactly on the top of my FJ40 to do list, especially after I've figured out which tank to put fuel in for the time being. It works for now, so I'll be working on other stuff on the vehicle for a little while. Today I changed the oil and only 4 quarts came out.

 

[Downey]

Ok then. I think I'd pull the rear tank out for now, plumb stock front tank directly to the fuel pump, then tackle your other projects. Hang on to the rear tank because it is rebuildable, and because it holds 22 gallons. It can be re-installed in the future with a sending unit that will let you read contents of either tank using a modified Sept 1972-older sending unit, an electric switching valve, and a double pull/double throw switch with your stock gauge.

 

[71hj40]

I took a look at this thread hoping it would explain what I have on my 71. I have what appears to be about a 2 (ish?) gallon fairly factory looking tank tucked behind my rear wheel well up under the quarter panel. It has some lines going to the main tank under the passenger seat, but no fill point. Is this just some kind of expansion/breather room tank or is it actually for fuel?
Don't mean to hijack just figure somebody watching this thread might know what is up.

 

[ErikinSC]

Need pics to help determine...

 

[71hj40]

You can see the tank through my back corner rust hole....lines come up through the back wheel well, run along behind the jump seat, then go back down through the body beside the filler neck for the main fuel tank.