Sub tank

[dpetersen]

G'day guys!
Quick one,
What does it mean when the sub tank light stays on after starting the car?
03 3lt model, both fuel tanks full.

[Bigcol]

the light on the switch - or the light on the dash.............................?????
switch - Houston, we have a problem
dash - Dang Houston we have a major problem

sounds like you need the 3L guys, or Ynot to help you - sorry I cannot

[dpetersen]

On the dash. If it means something with the transfer pump is stuffed that's ok, atleast I can still drive it!
Any ideas what it means?

[Bigcol]

from my limited knowledge about the black art of elektrickery

sounds like an earth problem for the sub tank unit
I think I read on here somewhere that ............
the light comes on when there is a fault with the sub tank sender...............

[dpetersen]

Hmmmmmm! Il have a look under it tomorrow!
My only other thought is that because I filled it up right to the top the other day and it's been sitting for the last two days in the heat of Alice Springs and the fuel has expanded and caused something to play up? Plausible? or just a stupid guess? lol

[gaddy]

Mine does this when I have the stereo and shower pump on and the fridge cuts in at the same time , start the car and sub tank light comes on , if I disconnect the battery for half hour or so all is good , I believe it's lack of earthing from chassis to body , sad bit is I keep forgetting to add the earth cable thats been sitting in the shed for the last 12 months , :)
Just my experience I'm no expert !

[dpetersen]

Yeah I just had a bit of a read about the lack of earth from the body to chassis.
Has anyone got any pics of how they've added a better earth?
Might try cleaning the connection from the battery negative to where it's connected to the body of the car and see what happens.

[Bigcol]

yeah, try and disconnect the pos lead, leave it for 10 mins, then plug it back on, and see if that helps
also
make sure battery terminals are tight (learnt this the other day)
no, leaving it in the sun will not affect it, so dont worry about that

on my old GQ, I had a lead from the gearbox to the chassis
the engine to the chassis
the one for the neg of the battery to the engine and chassis

they help

[Bigcol]

I mounted the one from the gear box on one of the bolts for the cross member - between the GB and the rubber mount, then over to a spare bolt hole on the chassis on left hand side

[dpetersen]

So I cleaned the battery terminals and disconnected the battery and also cleaned where the negative is connected to the engine and checked the fuse under the dash, it was ok but changed it anyways. Still no luck, sub tank light is staying on.
I don't think it's related but I do get a pretty violent shake when I start the car.
Any other ideas?
I'm gonna take a guess and say the sub tank is the one on the drivers side and not the one at the rear of the car under the boot?

[gaddy]

Time to wait for a guru , I got nothing

[the evil twin]

Rather than go thru it again, have a read thru this thread fro a week or so back.
It tells you how to fault find the codes etc to figure out what the Sub Tank Computer thinks is wrong

http://www.nissanpatrol.com.au/forums/showthread.php?32909-GU1-Sub-Tank-Switch&highlight=tank+light

[SKYLAB]

if it was fine before you fuelled up, youve filled the sub to the brim(ie over full) and the sub tank sender unit is giving mixed signals,,,
Solution is to syphon about 5-6 litres out, and in future, when filling, fill to the first click on the bowser nozzle and be happy with that,,,, dont top it right up !
Doesnt necessarily apply to main tank, as the main fuel pump works regardless.

[SKYLAB]

The "violent" shake is prolly because you fergot to let the mechanic out b4 you shut the bonnet, and he maybe fouling one of the belts !

[katwoman]

Searched forum. Can't find answer.
It seems my sub tank is syphoning itself into the main tank. Sub tank gauge going down. No obvious physical leaks. WHY ? What happens when sub tank is empty ? Will it cause problems ? I try to keep my subby full. Bugger the extra weight.

[Maxhead]

The sub tank pumps into the main tank every start up but its only a little bit





..........on the move

[Bob]

The sub tank pumps into the main tank every start up but its only a little bit





..........on the move

x 2..................... Kat

[katwoman]

Yeah, but I've lost half tank (40L) in about 500 Kms. I'm getting about 4l/100 ATM. You can almost see gauge move.

[Bob]

Yeah, but I've lost half tank (40L) in about 500 Kms. I'm getting about 4l/100 ATM. You can almost see gauge move.

From my understanding every time you start the Truck it test pumps from the Aux Tank .

I would fill both tanks and drive for say 200 K's and then fill both tanks again and ascertain your fuel usuage

[the evil twin]

Searched forum. Can't find answer.
It seems my sub tank is syphoning itself into the main tank. Sub tank gauge going down. No obvious physical leaks. WHY ? What happens when sub tank is empty ? Will it cause problems ? I try to keep my subby full. Bugger the extra weight.

Factory setup is with the sub tank is lower than the outlet.
This is done deliberately so it cannot syphon.

Was there a lot of stop/start driving in the 500 K's?
Some vehicles will transfer up to 250ml every time you start the vehicle if there is fuel in the Sub and the Main isn't full.
Most are around 100 to 150 tho.
Unless there is a fault the sub tank pump cannot fully empty the tank as the Computer won't allow the pump to run

FWIW I manage fuel by...
Fill both tanks (147 and 75),
Use about 1/2 the main,
Transfer the Sub over the next few days/hours till transfer stops (sub tank empty switch on the sender unit switches the pump off).
Use the main till a "fillup" and start again.

[katwoman]

Not alit of stop/start. No. So, if the car uses 250ml each time I would of started the car 80 times over 500 km ? Nah, I don't think so. It's never used this much before.

[Maxhead]

Not alit of stop/start. No. So, if the car uses 250ml each time I would of started the car 80 times over 500 km ? Nah, I don't think so. It's never used this much before.
I think you need to figure out your fuel usage to determine if you're losing fuel

[katwoman]

I think you need to figure out your fuel usage to determine if you're losing fuel

At the moment its bugger all, cos the sub tank is filling it !