• Cars travel faster on the highway and efficiency is bette...
    Cars travel faster on the highway and efficiency is better on the highway than in the city.
  • Check your tyre pressures after each fill-up.
    Check your tyre pressures after each fill-up.
  • Use the same petrol pump for consistency.
    Use the same petrol pump for consistency.
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Calculate your car's fuel efficiency correctly

1st Oct 2017 6:00 am

Is your car's digital readout giving you the accurate mileage? We tell you how you can calculate fuel efficiency of your car accurately.

"Kitna detI hai?" (How much does it give?) More often than not, that’s the first question asked about a new car. It's no secret that we are quite obsessed with fuel efficiency in India, and it's why car manufacturers highlight their official fuel efficiency claims on their brochures and in their advertisements. These figures are obtained by driving the vehicle on a rolling dyno (a treadmill for cars) according to a predefined ‘Indian driving cycle’. So, while the figures indicate the efficiency levels of different cars, they do not reflect the reality of driving on the road. Factors like traffic levels and road conditions, however, do alter this figure. And while many of us check the efficiency levels, and quite a few meticulously track efficiency with every fill, very few use the correct technique. Some of us even rely on the car's trip meter.

To ensure you get an accurate picture of your car's efficiency and how much you spend, here are a few points to bear in mind. 

To the brim
Filling the tank up completely is the only way to know the exact amount of fuel used. But simply relying on the automatic cut-off won't be very accurate. When you fill your car, the fuel gushes into the tank at a high speed, and, at times, all the air present doesn't escape out, thus you get a full tank, but with some air trapped inside. But modern fuel injected cars also have return lines for fuel not used and this complicates the matter even more. So, wait for a while after the cut-off and fill it again a few times. Also, if the fuel nozzle is dipped in completely, the flow stops as soon as the level reaches the nozzle. So, ask the attendant to rest the tip of the nozzle at the end of the fuel filler and fill it up.

Stick to your pump
Where you fill is as important as how you fill. For consistency, it is highly recommended that you try and use the same fuel station and dispenser too. Most fuel pumps are calibrated and accurate, but there can be slight variations between them. Additionally, changing the brand of fuel each time can affect fuel economy, as there is a slight difference in each brand. The preparation, additives, etc. differ from manufacturer to manufacturer and this can have an impact on efficiency. Also stick to company owned fuel pumps or ones that have a good reputation for maintaining quality.

Odometer and trip meters
Keeping a tab on the odometer and trip meter is vital to get the correct fuel economy. The odo records the total number of kilometres your car has done till date, while the trip meter allows you to record a specific distance you have travelled. Some cars also feature two trip meters – Trip A and Trip B. Use Trip A for each fill up and note down the reading along with the litres filled. Then reset the trip and follow the same procedure each time. For longer outstation trips, where you will have multiple fills, you can use Trip A to measure efficiency between each fill, while Trip B can be used to calculate the total trip efficiency.

Pay attention to the drive cycle
Any change to the driving cycle, like traffic and even vehicle load will impact fuel efficiency. If you wish to check your car's typical efficiency, try and use the same set of conditions. Avoid long detours and alternate routes. Try and standardize your driving speed and style too. Also, air conditioning has to be set at a constant as that contributes heavily to the overall economy.

Keep the car in check
Tyre pressure can greatly influence fuel efficiency. An underinflated tyre will be harder to rotate and will result in lower efficiency. A good habit will be to check the pressure during every alternate fuel fill. At well-maintained fuel pumps, the tyre pressure gauges are calibrated. Apart from this, maintain the car well as factors like a clogged air filter, dirty engine oil can all affect fuel efficiency.

Use technology
There are plenty of smartphone apps that can help you keep a check on your fuel records, service schedules and do all the calculations for you. There are apps that also log your fills and calculate the consumption against the GPS kilometre measurement. Relying on GPS can be accurate, but there may be satellite loss in some areas and that could affect your overall calculation.

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