FZJ80 1993 Double Tank Logic (1 Viewer)

[willorge]

Hello Everybody,

AS some of you know I just got my 1993 Japanese FJ80, in Ecuador. Its got an original Double tank feature, and I have some doubts. Yes, now I understand why it has two tanks, its a GAS GULPER, and its hard to deal with it coming from a 2018 2.0 TSI Volkswagen Tiguan! LOL!

So, brief and simple, I was surprised. These cars have had a lot of hands on them and I have my doubts. Being it so, it has two tanks, I filled both tanks and the SUB TANK drained frist before the MIAN tank. Is this the normal logics?? As an Airline pilot, It would make more sense to me that you use up the MAIN tank first, the large one and have the SUB TANK eat up LAST, as it would be your GET HOME SOON tank, or EMERGENCY FUEL one..... Is this the correct logic or has this car been manipulated?

Also, I live on a hill, and I parked my car the first night after my SUB tank had feeded and emptied out first, and parked on the hill. Next morning, my SUB tank was FULL again.... and the main tank was half or 1 quarter empty......

Any way, any insights on this would be great! Thank in advance!

Stefano Rota

 

[willorge]

Fed, not feeded, sorry, English is my second language, LOL

 

[CycloSteve]

My guess is that the two tanks are no longer setup as they were originally.

There are two basic setups that are factory:

1. The gasoline version, where you flip the subtank switch, and the fuel from the subtank is pumped into the main tank. This transfer should only happen if the main tank is below 3/4 full, and will automatically stop if 3/4 full or when the subtank is empty.

2. The diesel version, where flipping the subtank switch determines which tank feeds the motor.

What you are describing would be the two tanks being linked and auto-siphoning from the sub into the main, and then draining back into the subtank when parked on a hill. That would definitely not be how either factory system should work. You may need to take a look under the truck to determine how the tanks are currently plumbed between each other, and to the motor.

Which city are you in, in Ecuador? I have family in Cuenca, and there is a good Landcruiser shop there.

 

[mudgudgeon]

CycloSteve has it correct.

Sub tank should not drain until you hit the switch which activates a transfer pump to pump fuel into the main tank.

 

[Gun Runner 5]

Just curious, do you have the one door that contains the dual filler necks like a 105 Series or two separate fuel doors?

 

[willorge]

Hello Cruisers,

Replying to Steve! Thanks for the logic and it makes sense! I was really curious about this and what I am starting to believe is that the SUB TANK has its...... "valve" to the open position because you cant have a SUB tank smaller capacity to fill first.... its very particular to have this. So my car is a GASOLINE version, 1993, original tanks, and it has the button. Ill go to the car now and get some pics for later! BTW: Im in Quito, the capial, lots of nice places around, and a nice FZJ80 appreciators community around.

CycloSteve has it correct.

Sub tank should not drain until you hit the switch which activates a transfer pump to pump fuel into the main tank.

Thanks! So basically, the SUB TANK is not auto FED? It needs to be activated so it feeds my main tank and see the indicator rise? Thats why I was wondering, what the heck is the SUB TANK button for then!?

Just curious, do you have the one door that contains the dual filler necks like a 105 Series or two separate fuel doors?

Its one door with the lever to pull and fill up the other tank. Two indicators. In other words, a real factory Double Tank.

 

[mudgudgeon]

No, sub tank sounds not automatically feed into the main.
They can have problems with fuel syphoning from one to the other. Can't remember what the cause/ solution is though

 

[mudgudgeon]

Just curious, do you have the one door that contains the dual filler necks like a 105 Series or two separate fuel doors?

80 series with sub tank had a single fuel door, single filler neck with a valve in the neck to divert fuel to sub tank while filling.

 

[Gun Runner 5]

80 series with sub tank had a single fuel door, singe filler neck with a valve in the neck to divert fuel to sub tank while filling.

Sounds like an interesting setup.
I know some 105’s actually have dual filler necks behind a single door. You literally remove the spout from one tank and start filling the other. I have no idea how common this option was.

 

[AussieHJCruza]

Sounds like an interesting setup.
I know some 105’s actually have dual filler necks behind a single door. You literally remove the spout from one tank and start filling the other. I have no idea how common this option was.

All the dual tank 105's I've ever had anything to do with had that setup, and all the dual tank 80s had the switching valve.

 

[mudgudgeon]

Sounds like an interesting setup.
I know some 105’s actually have dual filler necks behind a single door. You literally remove the spout from one tank and start filling the other. I have no idea how common this option was.

Correct. Much simpler set up in the 105 series. No flap valve in the filler neck.

 

[Gun Runner 5]

With either setup, having that extra fuel capacity would be nice.

 

[george_tlc]

The factory transfer pump setup for the petrol 80 has 2 items that are electrically operated.

1) The transfer pump
2) Antisiphon valve

Both 1) and 2) are activated to transfer fuel. Stop the pump and the antisiphon valve closes to prevent fuel siphoning between the tanks.

So, likely in the OP's case, either someone removed the antisiphon valve or it is broken and stuck open.

Picture from my subtank install writeup:

cheers,
george.

 

[willorge]

The factory transfer pump setup for the petrol 80 has 2 items that are electrically operated.

1) The transfer pump
2) Antisiphon valve

Both 1) and 2) are activated to transfer fuel. Stop the pump and the antisiphon valve closes to prevent fuel siphoning between the tanks.

So, likely in the OP's case, either someone removed the antisiphon valve or it is broken and stuck open.

Picture from my subtank install writeup:

cheers,
george.

WOW! Now thats an explanation, grpahic explanation! Thanks!

So, I made a few videos activating the tank button in order to see if the noise is proper or not. Now, the thing is that in Ecuador, it is typical for mechanics to build everything EVERYTHING the other way around. Example. You hit the brake, your reverse lights come on, you hit Flashers, you Brake Light Brighten, ETC.

I would need to know how and where to check the connection for this maybe poles were inverted? (Sorry, shooting wild guesses)

1. My friend suggested something to try, and you can all bash our idea.....Feel free, no hard feelings, LOL
   
   
2. Turn on the car, and activate the SUB TANK
3. TURN OFF THE CAR with the button depressed
4. Turn the SUB TANK Button Off with Car Turned Off
5. Turn car back on???

I/we thought that could cycle the logic in the system? Any way, lets see, if not, Im open to suggestions.

Here the video from different angles






Stefano Rota

 

[willorge]

If any of you can figure out what might be wrong or if according to that sound, it sounds right, le me know! Thanks Guys

 

[george_tlc]

Sorry, but a few clunk clunk sounds is not going to help with anything...

As I wrote, there's a fuel pump (for the transfer) and there's a solenoid for antisiphoning.

You will need to verify what you have and whether it works by transferring fuel. Verify you have the factory pump/solenoid and verify each operates. You may have to bench test to be sure, especially if you have had monkeys fiddling with the system in the past.

My setup makes a small click sound (solenoid energizing) and a soft whirring sound (fuel pump pumping).

cheers,
george.

 

[willorge]

Sorry, but a few clunk clunk sounds is not going to help with anything...

As I wrote, there's a fuel pump (for the transfer) and there's a solenoid for antisiphoning.

You will need to verify what you have and whether it works by transferring fuel. Verify you have the factory pump/solenoid and verify each operates. You may have to bench test to be sure, especially if you have had monkeys fiddling with the system in the past.

My setup makes a small click sound (solenoid energizing) and a soft whirring sound (fuel pump pumping).

cheers,
george.

Thanks George, Ill be trying to figure this out soon then and maybe have to find out, and make better videos than CLUNK CLUNK sounds lol, any way, those were the only sounds made with the sub tank button pressed. Ill try again and better info.

Stefano