Extra Fuel tank possible on BJ40? (update 20/03/2026)

[Rogerr]

I have now 40 Litres under the non-driver seat.
Would it be possible to at another one under the BJ40 and combine both?
Somebody done this?

found this version tank:
Tank 110L
its a tank under both seats
regarding sloshing: all their fuel tanks have internal baffling to stop this from happening

Last update:
I ordered this LRA 110 litre tank
now 2-3 months waiting

 

[charliemeyer007]

Back about 1985 I stuck a 12.5 gallon tank behind the rear axle in my 72. The tank was from a Datsun b210. I made the supporting straps from 2" container banding. I cut a hole in the rear fender for the gas fill on the same side as my front tank, so I could fill both at one pump easily. I mounted my manual tank selector switch under my bench seat by the drivers side. It has a 3rd port option so I could select a trailer mounted aux tank with appropriate hoses/connectors - if desired.

I put a switch in the pre existing dash hole to select the gas gauge to read either front oem tank under the passenger seat or my rear aux tank. I bought an assortment of low ohm 2% resistors from radio shack. I was able to get the rear tank to read E which was empty and 1/2 which was full on the oem gas gauge.

Just this spring I removed the aux tank - it has some sort of leak from damage. Not sure I want to fix it or do something different. A local company has a 22 gallon tank that fits in the rear space. $650+ I really want to weld up a stainless steel tank for the space.

 

[Living in the Past]

Appears your exhaust runs front the right side to the left side behind the rear axle with the muffler in the center. That space is the most common place auxiliary tanks are mounted rerouting exhaust would be required.

 

[JohnnyC]

I think the tank that mounts inside the cab that replaces the stock tank with a 29 gallon that spans the pass to driver’s side is still available … but… VERY expensive and afaik it’s still not baffled

 

[jim land]

Some use 90s blazer or jimmy tank

 

[jim land]

A thread about that

Thread 'Fuel Tank Alternatives in 2025'

Apr 10, 2025

Morning All,

I messaged Jim (Downey Off-Road) last week and he said that his 22 gallon fuel cell is no longer available. I can't find anyone making one similar. Am I missing something? I won't be running a tank inside because I plan to build under seat storage drawers. Otherwise, the long range tank that goes under both seats would work. Also, the price on those...Holy Crap!

I do have an old, used Con-Ferr tank in storage somewhere that came with a bunch of spare parts that I bought 20 years ago. I have no idea what shape it's in. I figure that if someone removed it, it's probably...

• msapers
• Replies: 44
• Forum: 40- / 55-Series Tech

• 

 

[45Dougal]

I have a huge tank under both seats similar to the one linked. Mine isn't baffled, and half a tank (60kg) of diesel sloshing around is very noticeable.
Mine looks locally made, and you can probably find a local aluminium fabricator to make something that suits you (pref with baffling).
Mine is a bit too deep for me (knee room), and I'd rather have a bigger space in the centre to provide better access to transmission tunnel panel.
Otherwise works well - so long as its all well sealed up of course.

 

[Rogerr]

I have a huge tank under both seats similar to the one linked. Mine isn't baffled, and half a tank (60kg) of diesel sloshing around is very noticeable.
Mine looks locally made, and you can probably find a local aluminium fabricator to make something that suits you (pref with baffling).
Mine is a bit too deep for me (knee room), and I'd rather have a bigger space in the centre to provide better access to transmission tunnel panel.
Otherwise works well - so long as its all well sealed up of course.

this sloshing is a good attention point
is it filling up like communicating vessels?

 

[45Dougal]

this sloshing is a good attention point
is it filling up like communicating vessels?

Not as such since I only have the one tank, but it's the full width of the truck, and although the centre section is narrower than the ends, the fuel is completely free to flow around.
If the tank is half full and you go round a corner, then the weight shifts and you hear it woosh across.
If i was rebuilding one, I'd probably split it into 4 or 5 zones, with plates in between and a couple of 20mm holes to allow the fuel to move around slowly.
You could go full Concorde on this, and segregate your fuel system into 20 independently pumped zones, but that's probably overkill.