Outer Limits 4x4 Board

I have a 92 model 80 series landcruiser and lately when I fill the sub tank it seems to be feeding into main tank. the main tank gauge will read empty with sub tank gauge on full but if left over night the sub tank then reads empty with main tank then on half to 3/4 full so I am assuming that the fuel is some how flowing into the main ?????? any idea cause as far as I am aware they run independantly and the sub is only in use when button on dash is pressed ?

I have a 93 diesel and the sub and main fuel lines are completely seperate. When the sub button is pressed, the motor is fueled directly from this tank. However I have been told that with the petrol model, the sub feeds into the main tank first. I take it yours is a petrol? Also might be crap that I've been told.
Still doesn't explain your issue though. The overflow for the sub flows into the main and visa versa, so it is self siphoning some how. The breather might be blocked on the sub and forces it to siphon into the main.

sorry should have stated that its a turbo diesel.

the petol dose transfer when the swich is pushed. have you changed your tamks or modified them at all?

So if its a diesel it might be a problem with the overflow, self siphoning?

no mods done at all to tanks or fuel line\system is there any valves or accesories on the line that may need replaceing to fix the problem.

or it could be going back through the pump. is there any one way checks? i have a petrol so im useless sorry

the two tanks are very seperate, so when sitting over night I can't imagine anyway fuel could end up shifting tanks. Perhaps the valve in the filler neck is leaking, and you are filling both tanks when the knob is out. The guages are slow to react and you might be misreading them, or they might not be totally accurate.

I've seen cases when running off the sub tank, some of the return ends up in the main tank. That could be explained by a faulty solenoid though.

that was my thought, the fule pump has a feed to the pump and from the pump back to the tank, amybe if could be syphoning back via that....

I am pretty sure they pump a little fuel from the sub to main every time you start the car on a timer. The idea is to keep all the lines and valves lubricated, maybe the timer is shot and just keeps pumping. Get under it and have a listen.

Mine was also doing this , there are two electric fuel valves between the main and sub tanks that control which tank the diesal is drawn from and returned to. sometimes these valves don't close all tthe way and allow the sub tank to flow into the main tank.It could be some crap stuck in the valve or in my case it was just old and stuffed (540000 km).replaced both (could have maybe got awy with only doing the supply valve but didnt want to risk it )and no more problems -about $300 each valve.

fish2 wrote:Mine was also doing this , there are two electric fuel valves between the main and sub tanks that control which tank the diesal is drawn from and returned to. sometimes these valves don't close all tthe way and allow the sub tank to flow into the main tank.It could be some crap stuck in the valve or in my case it was just old and stuffed (540000 km).replaced both (could have maybe got awy with only doing the supply valve but didnt want to risk it )and no more problems -about $300 each valve.

x2 but i changed only 1 valve and a couple of months later changed the second valve and the problem was fixed. Toyota genuine parts= expensive

if the second tank fills slowly it is usually the return line valve that is having issues. You can get non-genuine two way solinoid valves. Have not got any for a while but use to by them for setting up duel tanks.