[ChiragM]

From what I understand, the fuel gauge in cars tend to hold on to the full mark even after a bit of fuel is consumed. It has been designed in such a way that it initially depletes slower to give the driver a false sense of better efficiency. Because of this, the gauge depletes slower in the first half and faster in the second. This means that when the gauge tells you that you have 50% of fuel left, you have much less than that.

I did not realize this and it took me off-guard during an inter-city trip recently. Starting this thread since I could not find one on the same topic.

Now here's what has left me scratching my head - I drive the new i20 N Line, and would like to know if Hyundai has gone a little overboard with the tuning of the fuel gauge. I have not noticed this perceived effect in other cars I have driven, more so in my Maruti Ritz. Did cars back then not have this?

I did a quick check with my i20 recently. The car has a 38L fuel tank, which means that when the gauge showed that it had depleted by 25%, the car should have consumed approx 9.5L of fuel. But when I filled it up, it gulped in a good 15-16L of fuel. That's a good 6L of fuel more than what it indicated (I filled up as soon as a quarter reduced on the gauge).

What I would like to understand is this -
1. Is this a thing in all cars? If yes, how much is the difference between indicated and actual fuel consumed? Why have I not noticed this in my Ritz?
2. Have other i20 users noticed this?
3. Has Hyundai overdone it in the new i20?
4. How does the reserve fuel play into this? Not sure if my fuel gauge reading is inclusive of the reserve fuel.
5. How do I read the fuel gauge accurately? Even the range is over-optimistic. So now I need to guess how much fuel I have and range left based on how much I have travelled?

[iamahunter]

Originally Posted by ChiragM

What I would like to understand is this -
1. Is this a thing in all cars? If yes, how much is the difference between indicated and actual fuel consumed? Why have I not noticed this in my Ritz?
2. Have other i20 users noticed this?
3. Has Hyundai overdone it in the new i20?
4. How does the reserve fuel play into this? Not sure if my fuel gauge reading is inclusive of the reserve fuel.
5. How do I read the fuel gauge accurately? Even the range is over-optimistic. So now I need to guess how much fuel I have and range left based on how much I have travelled?

Yes its with all cars.
Have experienced it in my Swift and Ecosport first-hand. Its more like 60:40 ratio. (60% fuel in the first half of indicator and 40% in the later half)

Also, do not totally depend on the range shown on the Mid, not just hyundai, but any car. It always keeps changing with the driving conditions.

After driving the car for a while, you will get estimate of how much the car would go in the full tank. Reset the Trip meters for ease.

[Turbohead]

2) Had a 2009 i20 diesel. The exact same behaviour was observed too.
1) So is the case for all the other cars we've owned so far.

We start hunting for a pump when the indicator hits the last quarter and ensure we don't hit reserve reserve under any circumstances to prevent damage to the fuel pump apart from getting stranded. Worked well so far.

[adisan]

Originally Posted by ChiragM

5. How do I read the fuel gauge accurately? Even the range is over-optimistic. So now I need to guess how much fuel I have and range left based on how much I have travelled?

Some observations in my Chevy Beat:

While filling, even after the gauge shows full, the tank takes almost 2 litres of fuel. This is the reason why the gauge seems to deplete slower after full tank.

Yes, as the tank gets emptier, the gauge depletes faster. When the final bar starts flashing, there is around 4-5 litres of fuel left. This seems to be purposefully done to make people fill the tank before it gets dangerously low.

I no longer see it as an anomaly, though I had doubts until I understood how it works.

[goandude]

I have an i20 for last one year and I note down the amount of fuel that goes into the tank to fill it to the cut off point.
The gauge is marked in 12 divisions and my records show as follows :-
2/12 37 liters go in
3/12. 32
4/12. 28
5/12 26
6/12 (half). 24
7/12. 22

I also believe that the tank capacity is 40 liters from here
https://www.automobile-catalog.com/m...back/2020.html

[Chetan_Rao]

The gauges are approximations, and NOT graded linearly or accurate down to last liter or fractions of it. The top quarter of the gauge lasts a lot longer than the bottom quarter on every single car I've driven, for example.

The approximations are especially true for modern electronic displays with digital block readouts instead of sweeping needles, where each block represents a certain approximated amount of fuel and the block stays lit whether you're near the top or bottom of that block w.r.t. usage. More than once, I've noticed parking the car overnight and the fuel gauge showing one less bar next morning.

The gauge also has no way to accurately represent 'top-ups' beyond full tank a lot of people indulge in. The gauge doesn't move for a bit after refueling, but you're still burning fuel just the same.

The only way you'll get a hang of what your car does is observe and correlate over time.

P.S. On our roads where you can be cruising one moment and crawling the next, the DTE indicator isn't worth the energy it takes to display. I'd turn that and instantaneous FE off on my car if I could

[sidpunjabi]

Originally Posted by ChiragM

2. Have other i20 users noticed this?
3. Has Hyundai overdone it in the new i20?
4. How does the reserve fuel play into this? Not sure if my fuel gauge reading is inclusive of the reserve fuel.
5. How do I read the fuel gauge accurately? Even the range is over-optimistic. So now I need to guess how much fuel I have and range left based on how much I have travelled?

I've owned an i20 for the past couple of years and you're right about this.

You'll also notice that once the fuel gauge goes below the halfway mark, the performance becomes a bit more 'economical' / laggy in terms of acceleration - more pronounced on highways and inter-city trips. I believe this is done to improve the FE and extend the range for the remaining fuel.

Personally, I ensure to keep it above the halfway mark if the destination is 100+ kms away.

[anandhsub]

In my Verna, the markings towards the top of the fuel gauge are wider than those near the bottom.

Hence have always assumed the top half of the gauge indicates more fuel than the bottom half. I dont divide the fuel equally amongst the levels since they are not indicated to be equal.

Not sure how it is in the i20 though.

[Dr.AD]

Originally Posted by ChiragM

From what I understand, the fuel gauge in cars tend to hold on to the full mark even after a bit of fuel is consumed. It has been designed in such a way that it initially depletes slower to give the driver a false sense of better efficiency.

This is not an anomaly. This is the inherent nature of how fuel gauges work. This is certainly not something that is "designed to give any false sense of better efficiency". This is the limitation of the physical design of fuel gauges.

Because of this, the gauge depletes slower in the first half and faster in the second. This means that when the gauge tells you that you have 50% of fuel left, you have much less than that.

Again, this is common in most (all?) cars. All fuel gauges are nonlinear. The magnitude of this nonlinearity depends on several factors, including the shape of the fuel tank. In some cars this effect will be more pronounced and may catch the driver by surprise, in some cars it will be less obvious. But this is how all fuel gauges work.

Basically the sender unit of the fuel gauge has an old fashioned float, which floats on the top of the fuel surface and sends the signals about fuel levels. Depending on the fuel tank shape and volume, the fuel level does not change linearly with the fuel volume. In other words, instead of directly measuring fuel volume, this float can only measure the liquid surface level, and that gives rise to this non-linear behavior.

Here is one article that explains it: https://auto.howstuffworks.com/fuel-gauge1.htm

In summary, this is not an anomaly, bur rather a well known and basic limitation of the fuel gauge sensors. This is certainly not something that is designed to give any false sense to driver. This is common in all cars, and over the time, one would get used to this. For most experienced drivers, this is a known fact and their brain already accounts for this when they interpret the fuel gauge readings and judge the amount of fuel left in the tank.

[ChiragM]

Originally Posted by goandude

I have an i20 for last one year and I note down the amount of fuel that goes into the tank to fill it to the cut off point.
The gauge is marked in 12 divisions and my records show as follows :-
2/12 37 liters go in
3/12. 32
4/12. 28
5/12 26
6/12 (half). 24
7/12. 22

I also believe that the tank capacity is 40 liters from here
https://www.automobile-catalog.com/m...back/2020.html

Thanks, this helps a lot!

I believe this is the European-spec i20 in the link which I think is more than 4m. A quick google search shows that the Indian i20 gets a 37-38L tank.

Originally Posted by iamahunter

After driving the car for a while, you will get estimate of how much the car would go in the full tank. Reset the Trip meters for ease.

Originally Posted by Chetan_Rao

The only way you'll get a hang of what your car does is observe and correlate over time.

P.S. On our roads where you can be cruising one moment and crawling the next, the DTE indicator isn't worth the energy it takes to display. I'd turn that and instantaneous FE off on my car if I could

Originally Posted by Dr.AD

This is not an anomaly. This is the inherent nature of how fuel gauges work.

Thanks. I may not have noticed this in the other cars I have driven because I have never really bothered to see how much the car has driven after filling it up, until I got this car.

[voldemort]

I don't think it's done to give you a false sense of security. The manufacturer knows that anybody can verify actual fuel efficiency by full tank method.

There are inherent limitations of the way fuel is measured that gives rise to this behaviour with the guages.

If you park on a steep incline, and leave it there for sometime, you might notice that the readings would have dramatically changed. I once parked my old Optra on a steep incline, and was pretty sure the gauge was at the quarter mark when I drove in. When I returned, the guage was at empty, and the low fuel indicator was on. Once I was on level ground however, the gauge was back at quarter mark and the low-fuel indicator was gone. This shows the limitations with fuel measuring methodology (unless it was just something wrong with the Optra).

In my Honda City this behaviour has been observed, though it's not very pronounced.

Also, I know some cars where, even though it shows empty and the needle is at the very edge, refilling it to full tank fills in less than the total capacity of the tank by several liters. Either the tank size is smaller than what the manufacturer claims (unlikely), or there was infact some fuel left even though it showed empty.

[VALLURIS]

Spot on Observation.

We own a 2019 Jazz CVT petrol and full capacity of the car is 35 litre's. Our car gives an average fuel economy of 13 in city traffic.

Full tank gives a total range of 420 kms. I observed that first half of the car usually gives around 280kms and once the fuel is half done the reading drops to 130/140.

When we refuel at half tank it consumes around 24 litres which is more than 70% of the total fuel capacity.

I have even raised this issue with Honda service guys, they checked the fuel gauge and confirmed everything is fine. I happened to check the same with other Jazz and WRV owners and they have mentioned similar observations.

Now I understand that this happens across all car brands. But not sure how this false fuel gauge readings really helps people ??

[arjithin]

Originally Posted by ChiragM

This means that when the gauge tells you that you have 50% of fuel left, you have much less than that.

Rule of thumb I follow is when the gauge tells that 50% left, I consider 1/3rd left.

Originally Posted by ChiragM

I did a quick check with my i20 recently. The car has a 38L fuel tank, which means that when the gauge showed that it had depleted by 25%, the car should have consumed approx 9.5L of fuel. But when I filled it up, it gulped in a good 15-16L of fuel.

The calculations based on fuel tank capacity may be worser considering some fuel is never available for usable range ( dead stock).
My Pajeros fuel display moves based on the incline of the road too !!

[universal]

Originally Posted by ChiragM

From what I understand, the fuel gauge in cars tend to hold on to the full mark even after a bit of fuel is consumed. It has been designed in such a way that it initially depletes slower to give the driver a false sense of better efficiency.

I've read that manufacturers tend to understate fuel tank capacity, and you could easily fill 5-6 litres more (up to the brim).

The gauge wouldn't budge from the top until I burned the excess 5-6 litres off. That's what used to happen with me.

[manchandap]

Another thing that I have observed with Swift and Scorpio:

• On a non stop highway drives (let's say of few hundred KMs), the fuel gauge will 'fall slowly' as compared to the fuel consumed, irrespective of quantity of fuel in tank. This might be related to the sensitivity of the fuel gauge.

I always assume some sort of error in fuel gauge readings and use it to err on cautious side. My Scorpio has 60 Liter fuel tank (as per manual) and the digital gauge has 8 bars to indicate full tank. This translates to roughly 7.5 Liters/bar. This coupled with the FE gives me an idea of how far I can go or how low I can go on fuel before i refuel.

I tend to be cautious with fuel especially when I am in an unfamiliar terrain i.e. tank up at first available opportunity.