Dodgy or faulty fuel gauges

[jet150]

Hey all, not sure if this has been covered before but my fuel gauge sux balls. When I have a full tank the first quarter drops slowly then after that it shows half but ive only done 185k's It still continues to drop rapidly even though I still have heaps of fuel.

Is this a common thing with our cars? Is there a way to fix it? Is it a fuel float or sender issue?

 

[unclepaulie]

yeah i dont think the gauge is linear

1st 1/4 takes a while, 2nd and 3rd quarters drop rapidly and last 1/4 takes it time.

probably due to the fact the measuring instrument is just a float, but the tank isnt of a uniform cross sectional area so the float drops in a constant rate but the volume of the tank doesnt drop uniformly.

 

[CANDEE]

Every car I have had, has had the gauges show differently... I know that both that Wynn has atm show completely differently.. I know its just a case of learning the gauge...

 

[fieldy107]

Mine have both been dodgey, exactly as paulie explained. Someone should come up with a better measuring device to put in our fuel tank

 

[mchieff]

I pulled mine apart and pushed the needle up about 1/8th of a tank. Now mine works like a real guage and the light comes on when it hits the empty line!
Win

 

[Lasiorhinus]

Im in the process of collecting data to make a fuel calibration card.

The gauge is accurate, but the lines marked are not a linear scale, they do not indicate quarters of a tank.

 

[jet150]

Im in the process of collecting data to make a fuel calibration card.

The gauge is accurate, but the lines marked are not a linear scale, they do not indicate quarters of a tank.

Good suggestion but I can't see how it's the marked lines that are at fault because the needle drops erratically. First quarter holds for a while then the 2nd and 3rd drop fast then I can sometimes do up to 200km on the last quarter.

 

[Lasiorhinus]

Like I said above, the scale is not linear. Even though the lines are evenly spaced, they do not indicate quarters of a tank. As I said, I am in the process of collecting enough data to figure out precisely how many litres is indicated by each mark, but it is not a linear scale.

What do I mean by linear scale?

A linear scale is where a certain movement on the gauge represents a consistent amount of measured quantity. Examples of this are kitchen scales. No matter where the needle is pointing, if you add 100 grams, or take away 100 grams, the needle will move the same amount. It matters not how much flour is already in the scales.

A non-linear scale, however, is different. If you fill the tank to full, then burn 10 litres the needle will drop a little. But if you have the tank about half full, and burn 10 litres, the needle will drop a different distance to where it would from a full tank.

The gauge does read consistently, as you've noticed, on every tank. The needle doesnt drop erratically, it drops very predictably. If it was moving at different rates on different days, you'd have a broken sensing system. But don't make the mistake of thinking 1/2 on the gauge equals 1/2 a tank, and so forth. It doesnt work like that. This is not a fault - there is a reason why no numbers are marked on the gauge!

 

[unclepaulie]

as shown below:

 

[Lasiorhinus]

Thanks Paul, I was going to draw up one of those myself but decided to make a coffee instead.

 

[Slinz]

Both of my Legnums' gauges have read identically, and both have been as you describe Rob.
I haven't had the guts to drive it until it runs out of fuel completely, but I've done a LOT of kms with the fuel light on, probably nearing 100 km :/

 

[NuffNuff]

sorry to dig up an old thread, but did anything come of this?


I just picked up my legnum, got about 300km out of the first 3/4 of a tank.

below is a brief break down on how that went

1st quarter seemed rather normal, like as if it was linear
2nd and 3rd were used rapidly
4th was slow.. VERY SLOW infact i got a bit worried and filled it up when i got to about 1/5th left, i only actually used 37L from the full tank I put in when picking it up. so there was easily another 20L in it

 

[aaron68nz]

I've owned a pfl Galant and now a fl Legnum and both fuel guages move exactly like yours Damian. When the guage needle is dead on the E mark I usually have around 12 to 13 litres left in the 60 litre tank. Or I suppose rather put, this is calculated on that I can put another 47/48 ish litres or so in when on empty. Same on both VR4s.

 

[Guest]

Yep, sounds perfectly normal for our cars.

 

[Nitephyre]

Yeah, it's goddamn annoying

 

[mfbamba]

more annoying is when you have the fuel pump changed and it is not set in properly so that when the tank is full, the needle sits below the 3/4 full mark.

 

[gilly]

I find the low fuel light comes on at odd times. Eg I'll have 1/8 of a tank left and the light will come on. But then 10 minutes later, the needle might have dropped lower, but the light has gone off!
There doesnt seem to be any consistency with my low fuel light! I once ran out of fuel when the needle was showing about 1/8 of a tank too.

 

[mills_88]

One thing i used to do (very obvious but might be new to someone, you never know) is reset one of the trip meters everytime i filled up. I then knew i could safely get 400km, 450km if i stretch it out or if i'm feeling really ballsy 500km.

However, since i hardly use it anymore i tend to just run it below half a tank and have learnt the gauge well enough to know when to fill up.

 

[mookers]

One thing i used to do (very obvious but might be new to someone, you never know) is reset one of the trip meters everytime i filled up. I then knew i could safely get 400km, 450km if i stretch it out or if i'm feeling really ballsy 500km.

I always do this, and enter the distance travelled and litres used into PetrolMonkey (others seem to use Fuelly) and keep track of everything.

 

[fieldy107]

I dont fill until the light stays on solid, at this point I know I can drive for about an hour before it wants to conk out.