Subtank Auto-Transferring Fuel (1 Viewer)

[CycloSteve]

This is an odd one, and looking for the Mud-thought-trust to help diagnose...my truck is auto-transferring fuel from the subtank to the maintank.

My setup is a gasser style subtank system from a FZJ80 in my newly converted to 1HD-FT truck. The subtank system worked for years fine with the gasser motor. Press the button, and fuel would transfer from the sub to the main. Sometimes a small amount of fuel would auto-transfer, but not much. The fuel line to the IP is the correct 13mm / 1/2" and the pickup in the main is the diesel one with the proper diesel sock, and a return line from the IP. The only mod to the pickup was adding the transfer tube for the sub so that when the sub is activated that it pumps directly into the main.

I am 200 miles into driving the truck this week, and the fuel gauge did not budge. Scratched my head, I was thinking that the level sender unit was bad. Pulled the sender tonight, and the tank was near full. Well, I definitely was not getting 70 mpg, so something was amiss. Tapped on the sub, and it was near empty. Went to the station, and the main took three gallons, and the sub took eleven. Both were near full when I filled them last week.

When opening the cap there is a slight vacuum, not pressure. The cap is a brand new Stant for a mid-90's Toyota Hilux diesel. When closed, it does allow for the vacuum to suck air, but does not vent pressure out. The vent on the main tank is the proper one way valve, with the arrow pointing away from the tank, which means that it is for the relief of pressure (this too is brand new).

So, my current thought is to not cinch-down the cap so that it vents both ways and see if the auto-transfer nonsense goes away. Long-term I need to figure out what else could be the issue, and if the fuel is coming across the tank vent line at the filler neck, or if it is being drawn through the subtank transfer assembly, thus meaning that the solenoid is not closing, or is being forced open with the vacuum.

 

[CycloSteve]

Just a quick check of my understanding of the venting system in a stock HDJ80.

1. The fuel cap only allows for air to enter the tank, not exit, thus acts as a vacuum release. This ensures that the tank equalizes pressure as fuel is used by the motor, and the tank does not collapse.
2. The tank vent that snakes it way into the frame in the rear only acts as a pressure release. This ensures that if the temperatures rise in the tank and the air heats that the tank does not burst.

I have ordered a new factory fuel cap, and also a replacement solenoid for the transfer assembly. Will install both this weekend and see if that sorts out the mystery transfers.

 

[roscoFJ73]

What year is the FZJ80? There is some info here about how the petrol and diesel fuel transfer differs.
Offroad 80's • View topic - Sub Tank

 

[CycloSteve]

1996 US market FZJ80 chassis, but the subtank system came from a GCC (Egyptian) truck of unknown year. The transfer system worked perfectly with the petrol for a number of years, but now just after converting everything to Diesel it seems to like to move fuel on its own.

I definitely understand the differences between the OE gasser and diesel setups. If changing out the solenoid does not do the trick, I will likely change everything to the diesel design (already have that pickup for the sub). I will know more this weekend when I swap out the solenoid parts.

 

[roscoFJ73]

Cant you run a test on the existing solenoid? Ive heard of the solenoid valves getting blocked so they neither open nor close properly.

 

[CycloSteve]

There is a FSM test procedure, but I need to pull it out of the truck first. Hoping to get that done this weekend. These do not look serviceable at all, thus it will likely get replaced, and have the part on order. My gut is that the solenoid is not closing, and that the E10 fuel (when it was a gasser) has done it's work to mess it up over the years.

Should that not work, I am planning on going with a gasser/diesel subtank hybrid. Essentially using the diesel lines from both tanks and switch over solenoids, but using the computer and switch from the gasser. This would allow the system to pull fuel from either tank like the diesel, but switch off the subtank if the main was either 3/4 full or if the sub was empty. That way, all that I would be doing is a bit of plumbing and minimal wiring at the transfer assembly. Though I prefer to have a transfer setup, this is my fall-back solution.

 

[CycloSteve]

Pulled and cleaned the solenoid today. It definitely failed the FSM test, where it should be closed when it has no voltage. Cleaned it with Carb cleaner and cycled it numerous times on a spare battery. It now opens and closes as expected, so it is reinstalled to see if it continues to work or fails again. Time will tell.

 

[roscoFJ73]

Did anything come out when you cleaned it? Sometimes they get a bit of sludge in there. It will go for another 20 years, they don't fail very often.

 

[CycloSteve]

No crud, cycling it on a battery seemed to help get it back into shape.

 

[Tapage]

and you like this way of work .. the gasser way ?

 

[CycloSteve]

and you like this way of work .. the gasser way ?

When functioning as designed, yes. I like to treat the subtank as a dedicated set of jerry cans, which can be transferred to the main when needed. If everything works as it should, I will keep the setup as installed, otherwise it is on to Plan B of getting a few more hoses and solenoids and going full-diesel on it being a selectable tank.

Was testing everything yesterday, and found that there was a leak on the added transfer line into the top cover of the main tank. Took that back to the shop who did the work (not VH), and they removed the solder and tig'd it as I had originally asked. I hate re-work. Will paint and re-install tomorrow, and everything should be back to normal / fingers crossed.

 

[gnarlynick2072]

It might stick again over time, I would look into getting a new one.

I had an issue on my diesel sub tank setup where the solenoid would not return to the closed position when current was removed. Cycled a few times and it would unstick until finally one day it never returned.

 

[CycloSteve]

It might stick again over time, I would look into getting a new one.

Definitely on the list of spares to get, especially as these types of parts at some point will be discontinued.

Installed the maintank cover with the repaired transfer line; TIG below, shortened, and sealant above. Gave it a fresh coat of paint and used stainless hex hardware, which made torquing down much easier.

Will see how the tank does now with auto-transferring.

BTW, what is normal pressure that folks have in their tanks when opening the fuel cap? Now that things appear to be fully sealed, there is a slight pressure in the tank. I do not know what the blow-off pressure is from the orange vent valve. It tested fine with a vacuum pump on the output-side, thus I assume that pressure should vent at a given point.

 

[doug720]

If it's not already buried, put some anti-seize on the SS hardware. While it's not as bad when threaded into mild steel, SS has a tendency to gall.

I have dual tanks on my 60, the second being a saddle tank. I use dual manual valves - return and supply. I can mix and match how I want to control the fuel supply, and can even use the engine fuel pump to move fuel between tanks by how the return valve is set - main or saddle.

No electrics, most options, and for me, works well.

Dual tanks are a great option, 2 separate fuel sources, which is nice if you are in areas of crappy fuel, you keep one tank full of good fuel, and run off the questionable. If an issue comes up, you are not stuck.