Sub fuel tank workings.

As quite a few know my 100 is "OZ" spec with factory sub tank. The problem for me is that I have no information as to how it works or what it does.
If I run the main tank down to less than 20km range left and press the sub tank button there id a definite "clunk" from the sub tank area. There is no dash light to show you are on sub tank or any movement from the fuel gauge needle, ( should there be?) Does the sub tank run to the IP or fill the main tank?, does it have its own sender?
It would be useful for me to be able to use this facility otherwise I may be carrying 60 litres of fuel I can't access.

Andy

Andy, as it has separate filler necks, it indicates two separate tanks, of course. So when you look at Toyo and the twin tank set up, there isn't an option for filling one tank to the other so it must be a change over design straight to the same IP inlet as the main tank. I can see fuel pick up and return on the diagrams for both tanks but the gauge is on another page somewhere. I am looking for that now. If there is a sender then clearly it feeds to a gauge on the dash. Probably the same one as the main tank.

Back when I have found stuff on change overs and senders.

Ahh, found the change over solenoids. One for pick up and one for return so it's basically the same set up as I have. Just need to find the sender unit.

Yep, it has a sender. So I guess that some part just isn't working quite right.

Our OZ market FZJ105 had the factory sub tank setup when we bought it. We had the sub tank swapped out for a 150L tank, but other than that the set up is as standard. The 105 doesn't have the flap valve to select which tank you fill, when you look at the filler there are two pipes that you can pump petrol into, the front one fills the main tank, the rear fills the sub tank.

We would fill both tanks and then set off into the outback. As the sub tank was the larger of the two, we would run on that first, keeping the main tank as the reserve fuel. To select the sub tank I would press the sub button, this would illuminate an amber SUB indication in the dash binnacle by the fuel gauge, and the fuel gauge would display the amount of fuel in the sub tank.

As we would get low in the sub tank, shown by the low fuel gauge reading, I would press the sub button and switch over to the main tank. I can do this on the move with no obvious affect to the fuel supply or power delivery. The SUB indication in the dash binnacle would go out, and the fuel gauge would spring back up to the full mark to display the fuel level within the main tank.

I've not had a play with this setup in an OZ market 100 series, but this is how it works in our 105. Perhaps try shining a torch into the dash binnacle and see if you have the SUB indication. I can't remember if it illuminates during the dash light self test during ignition switch on.

So in answer to your questions:
Yes, I would expect to see an indication on the dash that you've selected the sub tank.
Yes the sub will directly feed the engine when selected.
Yes the sub tank will have its own fuel level sender.

I don't know if there is an access panel in the boot floor to gain access to the sub tank fuel sender, or if the sub tank will need to be dropped.

Is your sub tank full? Have you run on it?

I rather think that the issue here Scott is simply that it isn't working. It does have a sub light. But the gauge doesn't seem to be responding to the different fuel level in the tank, according to Mr L.

Thanks for that Scott, it was as I thought. My illumination light does not come on when I press the "sub tank" button but there is a clunk from underneath when I press it. Its my guess that fuel is being drawn from the sub tank as the truck does not stop but its not registering. I'll try it over the weekend on the sub tank setting as the sub tank is full and see if it goes down with use. The dash display shows 297km available on the sub tank and about 40 on the main tank so we will see what happens.
this may be a corroded terminal problem on the sub tank so I will be searching for an access panel to check the wiring and also check the fuses.

many thanks for the help Chris and Scott.

Andy

Chris said:

..........So when you look at Toyo and the twin tank set up, there isn't an option for filling one tank to the other so it must be a change over design straight to the same IP inlet as the main tank. I can see fuel pick up and return on the diagrams for both tanks but the gauge is on another page somewhere. I am looking for that now. If there is a sender then clearly it feeds to a gauge on the dash. Probably the same one as the main tank.

Back when I have found stuff on change overs and senders.

Ahh, found the change over solenoids. One for pick up and one for return so it's basically the same set up as I have. Just need to find the sender unit.

Yep, it has a sender. So I guess that some part just isn't working quite right.

Click to expand...

Chris - it sounds like you have drawings, circuits to hand. Where can I find those

Like I said Steve, on TOYO?

Chris said:

Like I said Steve, on TOYO?

Click to expand...

Looked but couldn't find.......but I have received my combo diesel/water tank today......will post up some photos later on my build thread. Happy days

What? You're not on Toyo? I thought everyone was on there. It's a website with every Toyota vehicle by model variant and country with exploded parts diagrams, serial numbers and prices for parts in euro dollars that are usually not far off.

Have a look for Toyodiy

Can't quite recall how it works but you have to get someone to nominate you or something. It's been years since I did that. Just had a look and the HDJ 80 is the second most searched vehicle on there. You can go on for a look but you won't see the diagrams.

Chris said:

What? You're not on Toyo? I thought everyone was on there. It's a website with every Toyota vehicle by model variant and country with exploded parts diagrams, serial numbers and prices for parts in euro dollars that are usually not far off.

Have a look for Toyodiy

Can't quite recall how it works but you have to get someone to nominate you or something. It's been years since I did that. Just had a look and the HDJ 80 is the second most searched vehicle on there. You can go on for a look but you won't see the diagrams.

Click to expand...

That's where I looked and lots of info but I couldn't see where you were looking. Mind you I was looking in 100 series rather than 80 - that could explain a lot. If somebody nominates me do I get more access rights? Sorry for being ignorant it comes quite naturally to me