Fuel gauge from hell!!!

[county1985]

1985 County....I assume I have 2 fuel tanks, as I can see one under the rear and assume i have one in the rear of the wagon on the right side (???).
Anyways...gauge was showing almost 3/4 tank yesterday...put $100 in (roughly 60 litres)....Gauge actually went down to just under 3/4!!! First time I have ever put fuel into a car and ended up with a gauge that then shows less fuel!!
Had a great 300km round trip to Coalseam park...got home gauge on almost empty.
from googling stuff, if I have the 2 tanks, that would be around 130 litres (??)
Secondly, I cant find a switch, so am assuming if there are indeed 2 tanks, one drains into the other (???)
My plan is to fill the bugger up until it can take no more fuel....that will tell me how much it holds!!
Can anyone confirm anything about the 2 tanks please??? And, any ideas why the tank would show less fuel after adding more???

[JDNSW]

The second tank is certainly after market, and there are many different ways of arranging them. Best bet is to get underneath and figure out how the plumbing works. It is quite likely that the second tank is not gauged at all! (Mine wasn't when I bought it - is now)

Quite apart from this, the gauges are susceptible to electrical problems, most commonly earthing problems - both the gauge and the tank sender must be correctly earthed, and bad contacts in either place can give really strange effects as the resistance changes.

John

[Bushie]

Fuel sender is installed upside down ?

[Alex 110]

Fuel sender is installed upside down ?

More likely back to front. My arb lr tank when originally fitted they reversed the sensor so it read correctly only now of course the wires wore thru & it stopped working altogether.
Replaced it with the help of my local auto sparky & now it went totally in reverse (showed full when empty & empty when full).
Gave up after that & filled up on the trip meter.

Sent from my GT-I9505 using AULRO mobile app

[county1985]

Thanks guys. From what I can tell, the bottom tank just has an outlet line to the fuel pump....if this is the case, then i am guessing that the sender is in the RHS tank in the rear cab....if that is the case, i am assuming I have now a half tank plus a full second tank!...Time will tell when i do a full fill up :)

[wrinklearthur]

There are sender units that are wired opposite to each other ( I got caught with the difference between HQ and HJ Holden's sender units ) and the respective gauges are then made to be responsive to the opposite ways. Test your sender unit by wiring it up to the vehicle before you fit it.

The sender units have a coil made of a resistance wire ( Nichrome ) and as the contact ( wiper ) slides across the coils, the resistance varies with the resultant varying current driving the gauges movement.

One type has it's wiper that starts at the grounded end of the coil ( tank empty ) and moves towards the other end of the coil ( tank full ), the full coil has resistance at it's maximum when the wiper is at the ( tank full ) end with very little current flow through the gauge ( showing full ).

With the other type of sender, it's internal termination setup is reversed, the wiper starts at the fully wound end of the coil ( tank empty ) and the other end ( tank full ) is then grounded, the resistance is then at it's least with maximum current flow through the gauge ( showing full).

No!!! you can not reverse the wires on the outside of the tank to the sender to try make it work, the Nichrome wire coil has to be terminated the opposite way around within the sender itself.

Different manufacturers can use sender units that have more or less winds ( resistance ) of those coils, more winds ( finer wire ) show a more precise reading at the expense of the coils wearing out more quickly.

By the way, Nichrome can not be successfully soldered with 60/40 solder, it should be done instead with a silver solder.
.

[county1985]

thanks Arthur....
I went underneath her this morning and have found that all my above assumptions were wrong!! It would seem that i have one tank under the rear of the car and not 2 as I first thought!
In which case, the gauge may in fact be reasonably accurate!....
Will find out for sure tomorrow when i do a full fill up.
If it does turn out that I only have the 18 gallon tank, then i am pretty happy with the fuel economy!!....did basically 300 km's with a lot of it doing 80 up hills and only used about 60 litres!....this is better than my Lada Niva was :)

[county1985]

So filled her to the brim today....gauge showing 3/4 tank...damned thing took 89 litres!!!
What?!!!! I must have a bigger tank that I thought.....Last week she was just above empty and I put in 40 litres....have only done 40 k's since then!!!!

[mattmac]

My county fuel gauge has started playing up too- it now wont go above 1/4 and the low fuel light stays on- any ideas? I'm assuming a faulty sender unit?

[JDNSW]

The low fuel light is a straight switching circuit, so your guess of a faulty sender is likely correct. And the involvement of the low fuel light plus a very low reading suggests the float is either sunk or the mechanism is stuck. It is quite possible that removing it and examining it may show a simple, easily fixed mechanical problem.

John

[jimr1]

Hi I agree with all these comments , I would like to add one more , now this doesn't happen often , but It can happen . The float on the sender gauge can get fuel in It , making it sit lower then It should , so even with a full tank It would show less on the Gauge . This also happens on Carby's , and is very common on water tanks , and cisterns . Now i'm not saying this is your problem , but if you have checked everything else , It may be worth looking into !!..cheers Jim.. :)

[JDNSW]

Hi I agree with all these comments , I would like to add one more , now this doesn't happen often , but It can happen . The float on the sender gauge can get fuel in It , making it sit lower then It should , so even with a full tank It would show less on the Gauge . This also happens on Carby's , and is very common on water tanks , and cisterns . Now i'm not saying this is your problem , but if you have checked everything else , It may be worth looking into !!..cheers Jim.. :)

That is what I meant by 'sunk'.

John