Help required - Fuel gauge not accurate

Ed,

It is fine advise, but utterly impractical, as least in my case. I have sender in my long range mounted at side wall 1/4 from bottom. Not only I have to empty tank to do it, but also I have serious risk to contaminate my tank with dirt.

However I am interested in your last comment. AFAIK all senders are floating type or I am wrong?

Cheers
Serg

Thylacine, I haven't had it out yet (the float that is). I'm wondering if it is the type that slides up & down the sender, or they type that pivots. If a pivot type then I think your advice on bending / lengthening is maybe the way to go. However, if its a slidey type one I'm probably snookered. I might pull it out tonight and have a gecko but I think I need to lower the tank to do it.

Serg, I have only physically seen probably half-a-dozen sender units, and that would be over twenty years ago, so have little idea as to what is common practice these days. My comment related to noticing a 'warming-up' period in newer cars, where the guage took a few minutes to stabilise, creeping up all the time. This, to me, (Instrument Engineer) seemed suggestive of a capacitance-based measurement.

Louie, (do they still use Louie in their ads? haven't seen a Mortein ad for ages) if it's a slide-type there's not much that you can do. Personally, I'd go for accurate measurement at the bottom of the tank.


ed

Ed,

AFAIK all convenience senders today are floating resistive type. Some gauges, however, constructed with feedback loop instead of being simple calibrated ohmmeter. Kind of slow moving device that finds its place by referring to resistance of sender. Thus they can achieve two things – needle does not jump up and down when vehicle going sharp uphill/downhill or simply break heavily and in some models they can show reading even when ignition is off. Actually I believe that it is done mostly for trip computers to estimate “km to go” more accurately. As consequence it require some time to stabilize after refilling.

Cheers
Serg

I had a GQ patrol with 160L tank and had the same problem with that but I always just put up with it. Carried a 20L jerry on longer trips so was not a drama but with the 4skinner we just don't have the room so I don't do it unless its absolutely necessary. Them was the days when you could buy 160L of diesel for under $120.

Max, you are pretty well right about aircraft fuel quantity indication systems (fqis). I am a licenced aircraft engineer on all general aviation aircraft and also boeing 767s and 747s, and, although it doesnt help us here, its interesting (to some) anyway... most GA aircraft use a normal float system which as it moves, picks off different values of voltage or resistance, depending if its a potentiometer or a rheostat type. But boeings and airbus use a capacitance type. Its basically an inner and an outer metal cylinder where it measures the capacitance between the two. As the tanks empty, the height of fuel between the two changes so the capacitance decreases and so the signal to the gauge changes. With this, the computer can create a linear quantity independent of tank shape (programmed in), and also takes into account the specific gravity of the fuel... higher SG means you have more weight of fuel per volume...

As for this problem, if you really wanted to spend the time getting it right, the best solution would be to modify your float arm so it reads full scale- from empty all the way to full. Then get a variable resistor or calibrating box which can adjust voltages so that it sends the right voltage to your gauge so it reads correctly.
Once again i'm surprised that the manufacturer of the long range tank doesnt supply something like this as part of their installation. After all, long range tanks arent cheap and a totally useless fuel gauge as a result is pretty average really. I certainly wouldnt be happy after spending big bucks and having no idea how much fuel i have when i need to...

What beats me is why you have the gauge showing 1/4 when you are actually near empty ?

Did you fit the LR Tank ?

If not, Perhaps whoever fitted it over bent the float wire so the float hits the base of the tank when it reads a 1/4 of a tank ?
Basically not allowing the float to reach its lowest point.

I`d say it needs to be bent up.

Yes he said it has a long range tank.
I would assume that the float is at a different height in the new tank, and the new tank is a different shape. So the float could be touching the bottom of the tank when it has more travel to go until it reads empty as with the std tank. The long range tank may give more capacity being higher and/or longer but may give more ground clearance by having a higher floor. Or of course the float may be (and will be) in a different position/height, so who knows what it's reading unless you get a sender to suit or have the original one modified and calibrated to suit. Otherwise it's just a case of writing down conversions and putting up with it as mentioned earlier.

I know he has a LR tank !

I asked him if he fitted it !!

I have fitted my own in a hilux. when I removed the sender unit it was mounted on top of the original tank.

Whe I refitted it into the LR Tank it mounts on the side of the tank. Being carful which way it is screwed back in as (If I can remember) it can be mounted in any direction thus making the float travell either horizonatlly, vertically or at 45 deg.

Perhaps it is`nt mounted properly.

Mrbrush, I didn't fit the tank. It's been in since near new (fitted by Dept of Environment who were the original owner). Not sure what brand or anything, only that it is around 90L and we can travel about 900km on it. Haven't noticed if the sender goes in thru side or top.

Didn't get a chance to look at it yesterday so will check it out on the weekend now.

Not being smart sparky.
But I think I`d rather remove the sender unit before the dash.

Being a 4runner, And If it has a "Longranger" Tank in it, then the sender should be on the side and easily accessible.

I mentioned that in my first post about maybe being able to calibrate the gauge but his prob may be that the float is hitting the bottom of the new tank before it has reached its full travel. Hence why its showing it has fuel when its really empty.

MrBrush, he said he has a LR tank IN his car. If it's not installed, then maybe its sitting on his passenger seat?? Heh heh.

I'm pretty sure if you pulled the float out and with it sitting beside the tank moved the float arm up and down, you would get a fair idea of it's travel inside the tank. Then just lengthen/bend/modify the arm so it's sweep covers the full height of the tank. Install it and then either check out the back of a dash (from a wrecker to save pulling yours out) to see if it's fuel gauge can be calibrated and if not, see if you can buy a voltage adjuster/calibrator for your sender to be calibrated to your gauge. As i mentioned earlier, alot of after market fuel gauges come with this feature so you might try to get one from them, or fit an aux fuel gauge which can be correctly calibrated.
Cheers.

Tippa, The reason I asked if he installed it or not was to try and determine how the sender was refitted and or rebent into the LR tank.
OK, we now Know Louie did`nt fit it.
So perhaps whoever did fit it thought the sender unit did`nt need to be bent or readjusted to suit the new tank.
As far as I know you normally have to use your original sender unit to place into the LR tank .

And that is exactly what I did, Sat the float arm alongside the tank to see what it would be reading, and bent it suit as best as possible.
Ok, mine was a 128 ltr tank and the float could`nt even touch the bottom when I bent it, So when mine reads empty I still have around 20 ltrs left. But when full I can travell 250kms befor it decides to move off full.

Its all trial and error.
Cheers

MrBrush, sorry mate- i misunderstood you. I didnt realize you were asking whether HE installed it personally or had it installed.... I just assumed that it was installed, and he himself installed it and you were asking if he had installed it or it wasnt fitted yet... Typical prob of typing/texting where you can read it differently to what is meant. My apologies, i see where you are coming from with your question and i feel like a goose ha ha.
Cheers.