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Old 16th December 2010, 16:58   #1
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Default Fuel Gauge Accuracy - How reliable is it?

My new Gypsy's fuel gauge has an arc divided or broken into 4 bars. Considering that the capacity of the fuel tank is 40 liters, I expected that it would drop down one bar for every 10 liters. However when it shows up as almost empty (halfway down the bottom most bar) and I fill 19 liters (1200/- worth of shell Super fuel), it jumps to just below full. This means that when it is showing empty there is at least 20 liters left in the tank?!! i.e It drops 3 bars for 19 liters instead of 2 bars.

The fuel gauge makes me needlessly paranoid and worried about getting stranded every time. While it is ok in the cities, I may end up filling bad fuel on a long highway drive instead of pushing the extra miles until I find a good petrol pump like shell.

Is this normal or does it need fixing? What is the experience you folks have with other cars?

Can you guys also list your car make and rate it percentage wise for accuracy?

Thanks

Last edited by Ragul : 16th December 2010 at 17:13.
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Old 16th December 2010, 17:08   #2
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Default Re: Fuel Gauge Accuracy - How reliable is it?

I experience almost the same with my Figo. My fuel tank capacity is 45 and fuel gauge is divided into 6 bars. For first 200-250 kms the needle sticks between the full and the next bar and for next 200 KM it jumps three bars and am not too sure how it wants to divide the next 350-400 km (not too sure as I never emptied my tank) To cut the long story short, yeah it is generally very inaccurate.
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Old 16th December 2010, 17:12   #3
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Default Re: Fuel Gauge Accuracy - How reliable is it?

^^Happens the same, with my Pulsar 200's digital Fuel Gauge as well!
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Old 16th December 2010, 17:18   #4
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Default Re: Fuel Gauge Accuracy - How reliable is it?

On my OHC vtec its pretty consistent and reliable.
Of course you have to be on a level surface.
Incline = less reading shown than actual
Decline = more reading shown than actual.
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Old 16th December 2010, 17:37   #5
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Default Re: Fuel Gauge Accuracy - How reliable is it?

I had this strange issue in my ikon once. With fuel bar reading at slightly less than a quarter tank, I managed to run out of fuel!
Car didn't crank up though I kept trying for 5 or 6 times. I had to take an auto rickshaw to the nearest pump and that guy wouldn't give me petrol in a bottle (as it was diwali night) due to security reasons.
Finally, the auto driver convinced the pump fellows to lend me 600 ml.
With 600 ml in the tank, one turn of the ignition and my car starts off. I drive right in to the pump and tank up.
41 litres later, the pump attender says, tanks full.
Now my tank capacity is 45 litres. This let me perplexed. The only reason I could think was probably, some bunk somewhere has dispensed 4 litres of water that has gone to the bottom of my petrol tank. This could mean that those 4 litres of water are still there at the bottom. Needless to say, the next service, I intend to drive in almost empty and ask them to check the petrol tank completely for water.

So I'm back to my earlier practice of tank up when the needle rests mid way!
But this is what I've seen my needle showing.
When at 3/4ths normally 10 - 11 litres are combusted.
When at mid way - 25 - 27 litres are gone.
When at 1/4th level - almost 37 - 38 litrest is what it takes to tank up.
Old stuff with improper calibration. I must probably try to get a dip stick mechanism like the auto drivers, that I can insert in the throat and see how much of fuel is left.
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Old 16th December 2010, 18:33   #6
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Default Re: Fuel Gauge Accuracy - How reliable is it?

@Ragul - I guess there's always some fuel-gauge inaccuracy in most sub 10L vehicles, but a margin of 20 litres seems too much.

What you could do is: Calculate your highway mileage, then multiply it by, say, 32 (8 litres left in the tank), and drive for those many kilometres each time before filling up again. Of course, as you said, this would need to be done on highways only and would involve the hassle of keeping an eagle eye on your trip meter rather than your fuel gauge.

Cheers,
Vikram

Last edited by comfortablynumb : 16th December 2010 at 18:36.
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Old 16th December 2010, 20:30   #7
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Default Re: Fuel Gauge Accuracy - How reliable is it?

I just had an idea. I will wait till she goes really really low, then I will do a full tank and measure how many liters were filled. That will give me a better estimate of margin of error. then I can take this up with 'em folks at "Meroodi" - no hopes of getting a fix but at least I can try.

The other option is to drive to to the A.S.S when very low on the gauge and remove the tank and check. It is only 1/2km form my house, so not a problem.

Cheers
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Old 16th December 2010, 20:44   #8
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Default Re: Fuel Gauge Accuracy - How reliable is it?

In my indica its pretty stable till half mark after which it drops rapidly, i got fed up with it and opened the tank float myself and deceased the angle of the float rod (made it straighter), so finally after two-three adjustments i got it as accurate as much as i could, now i can guess the liters in the tank by a margin of 1-2L by looking at fuel gauge, (before it was 5-7L).

Last edited by jav : 16th December 2010 at 20:48.
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Old 16th December 2010, 21:23   #9
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Default Re: Fuel Gauge Accuracy - How reliable is it?

My Alto has a 35 litre tank. My practice is to fill to the brim, even by giving a couple of shakes to allow trapped air to escape. When I do this, the needle settles at the very top, slightly above the max mark. During highway drives, I have noticed it stays right up there for the first 90 - 100 KM, after which it starts to move down gradually. Assuming a highway mileage of at least 20, it takes about 5 litres of fuel to make an impact.

My conclusion is that the gauge will be accurate to about +/- 5 litres. Don't rely on it completely and err on the side of caution. I don't know about the lower half of the tank, as my car never goes below the half level mark! But a service advisor at ABT once told me that when the needle touches the E mark, there will be approx 5 lires of fuel in the tank. I will take that only with a pinch of salt.
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Old 16th December 2010, 21:46   #10
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Default Re: Fuel Gauge Accuracy - How reliable is it?

There is always inaccuracy with fuel gauge, I have owned 3 cars till now and based on my experience i am making this statement.

My experience:-

When you fill up the tank full, to reach half way mark it would take much time(more KM) and once it reached half way mark it would come down soon. whenever fuel tank shows half tank it actually doesn't mean that it has half tank of Petrol/Diesel( if tank capacity is 70L and if shows half tank its doesn't mean you have 35L), it will always have lesser petrol/Diesel. When you fill up the tank full when the reading shows half tank you would realize this.
I am not sure what is the idea behind it but most of the car shows like this. I am not sure on the gauge accuracy of modern digital meters, the above experience is based on legacy meter gauge.

Maruti badly misses the low fuel warning light, nowadays most of the cars(Tata, Hyundai, Toyota) I know has this feature. What would it take for Maruti to add this simple feature??

Last edited by camchennai : 16th December 2010 at 21:47. Reason: Added one more line
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Old 17th December 2010, 23:30   #11
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Default Re: Fuel Gauge Accuracy - How reliable is it?

The guage is connected to a float switch which moves up and down with the level of fuel. And level is not same while driving. Its even worse in Hilly areas.

So my best bet is to stick to tank full to tank full theory. and make a habit of filling it with Oddo reading.
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Old 18th December 2010, 00:31   #12
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Default Re: Fuel Gauge Accuracy - How reliable is it?

Quote:
Originally Posted by jav View Post
In my indica its pretty stable till half mark after which it drops rapidly, i got fed up with it and opened the tank float myself and deceased the angle of the float rod (made it straighter), so finally after two-three adjustments i got it as accurate as much as i could, now i can guess the liters in the tank by a margin of 1-2L by looking at fuel gauge, (before it was 5-7L).

Does it entail crawling under the car each time? Assuming my fuel gauge is erring on the positive side, do I need to increase or decrease the angle?

Reading this now: HowStuffWorks "How Fuel Gauges Work"

Cheers
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Old 18th December 2010, 08:09   #13
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Default Re: Fuel Gauge Accuracy - How reliable is it?

I had an observation, if you add fuel additive like system D, then the fuel guage used to show always less fuel than the standard. May be its something to do with the float.
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Old 18th December 2010, 08:35   #14
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Default Re: Fuel Gauge Accuracy - How reliable is it?

Quote:
Originally Posted by camchennai View Post
Maruti badly misses the low fuel warning light, nowadays most of the cars(Tata, Hyundai, Toyota) I know has this feature. What would it take for Maruti to add this simple feature??
My Swift has a low fuel warning light!
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Old 18th December 2010, 16:45   #15
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Default Re: Fuel Gauge Accuracy - How reliable is it?

Quote:
Originally Posted by carboy View Post
My Swift has a low fuel warning light!
I guess newer generation swift comes with low fuel warning light, My friend owns a Swift which was bought about 4 years ago and it lacks that feature.
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