Gas tank guages

[ORSM45]

orrighty then,

i just put 3 gas tanks in my FJ, and i am running 2 of them together and the other 1 on its own.

the 2 that are running together are a 63L tank and a 99L tank. the 63L tank has a smaller diameter than the 99L. and the tops of them are level. therefor the 63L will run out before the 99L on the principal that it is higher.

now the question is can i run 1 guage between those 2 tanks?

the guage says 0-90ohms 0 = full 90 = empty.
BUT if i run the sensors in parallel then total resistance from the tanks when empty will be 45 ohms.
if i run them in series, it will be 180 ohms.

so is there any way of doing it. running the guage off the 99L tank wont be accurate until about lower than 1/4 tank so is pretty much useless.

thanks for any info and for actually reading that rant.
MaccA

[chimpboy]

If the two tanks are actually connected so that they form one single volume of fuel (ie fuel can flow freely between them), you should use only the sensor from the larger tank.

Only thing is that it won't be 100% linear ie the top half of the gauge will represent a bit more fuel than the bottom half. It'll work though.

Jason

[ORSM45]

ah yeah, so does the sensor go by liquid volume?
the fact it wasnt linear was why i was asking so that it could have possibly been more accurate. throughout the range.

if i ran the sensors in series, then put a 180 ohm resistor parallel to the sensors, it would work out to be 90 ohms on empty. (which is what i want)

| _| <---2 sensors operating here (move slow because of more volume)
|~| <---1 (99L) sensor working here

this will work,

but you recon i only need to run 1 sensor off the larger tank?

thanks for the reply.

MaccA

[chimpboy]

The fuel sensor works by floating at the top of the fuel so it tells you how high the top of the fuel is in the tank. If two tanks are joined together the fuel in both tanks will always be at the same level (until the smaller one's empty).

I really wouldn't worry about the gauge not being 100% linear as that is pretty much always the case anyway. I've never driven a car where you didn't have to get a bit of a feel for the fuel gauge.

Using two sensors plus a resistor means three components that could fail individually without you noticing. At least with just one sensor you know if it's dead. If you have all three hooked together, any individual one could fail and you'd still get a (bad) reading on the gauge.

Less work, better result. Win win!

Jason

[ORSM45]

very true, i never looked at it that way, less is better. ive never driven a car with an accurate guage now that i think of it.

were you talking about the operation of a petrol sensor or a LPG sensor?

MaccA

[chimpboy]

Oh... petrol was what I meant - to used to talking to yanks online who all say "gas" when they mean petrol.

Hmm with gas it would be even better wouldn't it? The pressure tells you how full the tank is no matter what size it is... I assume.

I don't know that much about LPG setups.

Jason

[marin]

i thought it was pretty much the same as a petrol tank, due to it being a liquid. After i have been going over bumpy tracks and look at the gauge actually on the tank, it is all over the place as the liquid swishes around, you can hear it moving

[ORSM45]

yeah thats why you have to angle the tank at 30 degrees from vertical.
ill try the easyier way (1 sensor and see how it goes) will probably be in a few weeks tho coz i have to get rid of alot of gas.

[RaginRover]

yeah thats why you have to angle the tank at 30 degrees from vertical.
ill try the easyier way (1 sensor and see how it goes) will probably be in a few weeks tho coz i have to get rid of alot of gas.

You will get the hang of it, your odometer will be a better gauge anyway
and I find the gauges change with ambient temperature which leads to a bit of error, mine broke after a while and I just used the odometer which I guess you will get the hang of after a few tanks.

BTW where did you get the tanks sounds like a neat little setup, got them in the back or under the floor ?

Cheers
Tom

[mav]

why not have one gauge and a three way switch to check each tank, this has got to be the cheapest and easiest way.

[ORSM45]

raginrover:

i got the tanks from a wrecked car i bought for parts. got em checked and now they have 10 years left on them. they are mounted under my tray (i could mount another 100L under there but i wanna get coils in that space.)
im gonna take the 63L out coz i wanna cut my chassis and its causing a little too much body lift in my tray. 190L is enough (150L usable.)

mav:

technically no, i dont have a 3 way switch but i already have 3 guages. 2 of the tanks were running together, so i just wanted to see if i could use these 2 tanks as 1 body of tank.

thanks for all the replies tho.

MaccA