[mjothi]

One question.
The milage can be calculated only when we keep filling the tank full for every fill right? What if we fill say 500rs in between and then tank full sometimes? In this case, how should we calculate the milage? Any idea?

[madbullram]

okay: Lets say you filled for 500rs so 10 liters (assumption).

Note: I am assuming you did tank full till this 500 rs refill and you had set your trip meter to 0 or noted down kms travelled in your Odo

1. Fill for 500rs (10 litres), dont reset you trip meter to 000
2. Drive till you have a need to fill
3. Now fill tank full.
4. Make a note of Petrol filled (assume 20 ltrs)
5. Note the total distance traveled in the trip meter

Now calculation.

Lets assume you have travelled 350 kms from you last full tank

Total distance travelled = 350 KMS
Total Petrol Filled = 10 (500 rs) + 20 Ltrs = 30 Ltrs
Total Mileage = 350 / 30 = 11.6 kmpl

This is what I do.

[mjothi]

Originally Posted by madbullram

okay: Lets say you filled for 500rs so 10 liters (assumption).

Note: I am assuming you did tank full till this 500 rs refill and you had set your trip meter to 0 or noted down kms travelled in your Odo

1. Fill for 500rs (10 litres), dont reset you trip meter to 000
2. Drive till you have a need to fill
3. Now fill tank full.
4. Make a note of Petrol filled (assume 20 ltrs)
5. Note the total distance traveled in the trip meter

Now calculation.

Lets assume you have travelled 350 kms from you last full tank

Total distance travelled = 350 KMS
Total Petrol Filled = 10 (500 rs) + 20 Ltrs = 30 Ltrs
Total Mileage = 350 / 30 = 11.6 kmpl

This is what I do.

Thanks man. I will TRY to follow this. I have an excel which is ALWAYS outdated

[prabhusati]

Excellent format for capturing expenditure on your vehicles. Thanks a ton to all who have shared their IP

[ravibhat]

Calculating FE is very simple, Best way is use same bunk which you trust most.

First time do tank full I mean really tankfull by shaking the car as well. Also make sure you have started from ZERO in Bunk reading because If they had filled 2 ltrs Petrol for bike they would not reset it for cars since at least 10ltrs petrol car owner will fill. so chances to cheat him is easy.


First fill full tank and drive for 50kms and then do full again and drive for 50km. Repeat the same thing 2 or 3 times. During every fill note down kilometers travelled and quantity of fuel filled. Take average of all those 4 or 5 times you filled the tank.

I do the samething when I calculate FE for my cars. After I stopped using Shell from last 3 months FE has come down by 1.5km :( which indicates either quantity or quality is missing.

Regards,

Ravi.

[anuragn]

Hey guys, I don't understand the need to shake your car for full tank filling. It's simply hilarious!
Fuel being a liquid always gets emptied (consumed) from higher level to lower level in the tank. So whenever you are going to top up the level, it is only the top empty space of the tank that gets filled up and, being a liquid, automatically takes the shape of the container. Remember the science funda we were taught in class 3 or 4 in school? It still holds true!
Getting out trapped air could be true only when the tank is completely empty right upto the fuel pump inlet, and there is air trapped in the fuel lines.

Anyways, coming back to the point, to ensure same level of "tank full", I always go to the same fuel station and try to refill from the same pump, same nozzle, using auto cut-off method. And best is to maintain a log of all refills, and then calculate FE over a few thousand kms. This averages out the -ve and +ve errors to almost zero.
And I do get 16.3kmpl in my Wagon R.

[kiranpashtakar]

Old thread, anyways here's my two bit, what anurag is suggesting gives a fairly good indication of the FE over a longer periods meaning more than lets say 20 refills. However there is a anomaly with the method when reviewing FE for 2 or 3 consecutive refills. The autocutoff gets activated faster when you pump it up in hot afternooon and later if you pump it up in the late evenings or early mornings. This is due to the higher vaporisation of the petrol during hot weather.

Also the density of petrol is lower when it is hot and higher when cold. Which means that there is a marginal difference in the volume depending on when you tank it up. This could also bring very slight or negligible differnce in the FE figure's

[anujatwork]

Originally Posted by Harrie

Or get yourself a Skoda or Mercedes, put your trust on german engineering and take the FE values from the MID.

The average FE reading on MID is since the last reset or for limited KMs, say last 50 or last 100?

[allwynkingsley]

Digging up a really old thread as I still haven't seem to not have got my answer.

So my question is, what is the practical and more accurate way to get real-world FE for my vehicle? I've no issues in maintaining records of fills & ODO readings. And, no issues in getting to a petrol pump from any of my usual locations.

I used to follow this during my good old college days,

-> Usually drive till vehicle indicates "low fuel" and reset trip meter. Useful for getting the odometer reading right. I subtract the current trip reading from current ODO reading to get the exact ODO reading when I hit "low fuel".
-> Fill for round figure usually hundreds or thousands on next visit to fuel pump. Note down the volume of fuel filled.
-> Log the ODO reading & volume of fuel filled. I get the distance covered by subtracting 2 ODO readings from the log & the fuel filled inbetween them.

I thought this is the best method to get real-world FE for my vehicle.

Then one day I stumbled upon an app which boasted of using "tank-full" method as being the most accurate. I still seem not to have my head around on how that is better than what I used to follow, especially considering dependency on auto cut-off, having to fill to the brim, etc.,..

Is there something I'm missing?

[Jeroen]

Originally Posted by allwynkingsley

Is there something I'm missing?

How accurate do you want it to be?

Your method seems fine. I take a slighly different approach. I just use the auto cut off and record whatever went in. The cut off point is actually pretty consistent and variation are less then a few 100ml. I only record the mileage once, when I fill up. So I only record mileage and liter filled and just compare to last.

What makes the measurement more accurate is to measure over larger distances and thus also more liters used. And subsequently averaging the calculation.

Truth is: the biggest inaccuracy tends to be the recording of your miles/kilometers. Whatever error your speedo has, the same error will be present in your FE calculations. That error is also depended on the tyre size and even the pressure of your tyres.

There is also an inherent error in the liters pumped. Not sure how accurate Indian petrol pumps need to be. Depending on the type of pump, it could be temperature depended too.

Which makes a discussion about using the auto cut off versus stopping at a round number fairly academic.

Irrespective, my earlier statement does hold: make the measurement, i.e. the liters used and the miles/km as large as you can get.

Good luck
Jeroen

[self_driven]

Originally Posted by allwynkingsley

Fill for round figure usually hundreds or thousands on next visit to fuel pump.

For my cars, I follow tank full method most of the time. When it is not possible (college kid, you know ) I fill in small quantities during the month and get a tank full whenever I need to calculate the mileage.

It's not necessary to fill to the brim every time. You can fill partially, note it down and add that quantity to litres of fuel consumed when you go for the next full tank.

My bike has a digital fuel gauge which blinks when it hits reserve. Problem with that is that the reserve warning goes off at times after going through bumpy roads and comes back after 3-4 kms on smooth roads. This makes it difficult to calculate accurate FE based on reserve method. Auto-cut method is much more accurate in comparison.

[pganapathy]

Originally Posted by allwynkingsley

...
Then one day I stumbled upon an app which boasted of using "tank-full" method as being the most accurate. I still seem not to have my head around on how that is better than what I used to follow, especially considering dependency on auto cut-off, having to fill to the brim, etc.,..

Is there something I'm missing?

Tankful to tankful is just easier because much less calculation is needed, but there is no real difference. You just need to note down the quantities correctly and calculate at the time you do a full tank. Of course, there is speedo error and full tank (auto-cutoff) does mean you cant pay a round number, but overall the system is pretty accurate

[airwarrior]

A wide range of discussions on why/why not we have an actual fuel consumption indication in our modern cars is out there on the www. Cost is quoted as one reason. But we now have affordable "Fuel Flow Sensors" and these are even available on Amazon. So why are OEMs not installing these in the new cars ? Instead most cars now have a "Distance to go" indication.

[alpha1]

Originally Posted by airwarrior

A wide range of discussions on why/why not we have an actual fuel consumption indication in our modern cars is out there on the www. Cost is quoted as one reason. But we now have affordable "Fuel Flow Sensors" and these are even available on Amazon. So why are OEMs not installing these in the new cars ? Instead most cars now have a "Distance to go" indication.

As a driver, the immediately useful measure is how long before refuel required.
Giving a flow rate measurement might be a good indicator but not helpful - since one already has an idea that the more one presses the accelerator, the more air intake is allowed, according to which more fuel is metered in the engine cylinder.

[airwarrior]

Originally Posted by alpha1

As a driver, the immediately useful measure is how long before refuel required.
Giving a flow rate measurement might be a good indicator but not helpful - since one already has an idea that the more one presses the accelerator, the more air intake is allowed, according to which more fuel is metered in the engine cylinder.

@Alpha1. Appreciate your advice esp coming from a senior BHPian. This subject has been widely discussed in this forum and I would not be adding any value. But I have found the Distance to Go indication is often deceptive- from a low double digit it often jumps to a three digit after a few kms of getting onto to a highway from a city landscape. The fuel gauge is analog and it's indication often does not add up to the average digital Fuel Consumption Indication and Distance to Go. So I agree that the digital fuel consumption indication is entirely based on driving conditions, but what would you infer --for eg your Distance to Go indicates 50 km and the fuel gauge shows a quarter tank (40ltr capacity so 10 ltr balance) the average fuel consumption is 16 km --- should I trust the Distance to Go or the fuel gauge and average fuel consumption?
The math does not work out. This is when I felt we could do with a Digital Fuel Gauge coupled with a Fuel Flow Indicator.