How I managed to extract 25 km/L fuel efficiency on my Sonet diesel AT

The Sonet 1.5 CRDi VGT 6AT engages the 6th gear at 75 KMPH. Therefore, setting the cruise control to that speed will fetch you maximum fuel efficiency.

BHPian AbidIqbalShaik recently shared this with other enthusiasts.

Extracting the maximum fuel efficiency from an ICE car on highways is not rocket science and I’m sure many people here know how to get the best fuel economy from the Sonet’s 1.5 CRDi VGT 6AT drivetrain. However, for those who are new to this vehicle, here’s a quick tip to get the best fuel efficiency from the car:

1. Driving At Lowest Possible RPM In Highest Gear Is The Key

• Usually, to get the highest fuel efficiency, your car has to run at the lowest possible RPM of the topmost gear. That means this drivetrain of the Sonet needs to run at the lowest speed of the sixth gear. The Sonet 1.5 CRDi VGT 6AT engages the 6th gear at 75 KMPH. Therefore, setting the cruise control to that speed will fetch you maximum fuel efficiency.

2. Driving At 75 KMPH Will Cause The Car To Shift Gears Back And Forth

• However, if the car, due to an incline, slows down even a bit, the gearbox will shift down to the 5th gear to attain the momentum before it comes back to the 6th gear. This back-and-forth gear shifting happens quite often if you set the cruise speed to exactly 75 KMPH. That is not only uncomfortable but it will also reduce the fuel economy as well as stress the gearbox.

3. Driving At 78 KMPH Is Optimum To Get The Maximum Fuel Efficiency

• Setting the cruise control to a speed that is 2-3 KMPH higher than the lowest speed the sixth gear can run at, will solve this issue. With that in mind, 78 KMPH is the optimum speed for you to extract the maximum fuel efficiency from the Sonet 1.5 CRDi VGT 6AT. At that speed, even if you are going over an incline, the car will not go below 76KMPH. That means it won't shift to the 5th gear during an incline (note that it will still shift to the 5th gear if the incline is very steep).

4. You Can Get Almost 25 KMPL On Highway With This Method

• I’ve tried this out and it has fetched me a fuel economy of 25 KMPL on a 40KM drive on Hyderabad’s ORR. In comparison, I get around 21 KMPL when I drive the car at 99 KMPH (that is the speed at which I used to travel on ORR as 100 KMPH is the speed limit on that road). Since I found this out, I’ve been driving at around 78KMPH on highways and I’m extremely pleased with the fuel efficiency I’ve been getting.

5. A Few Variables You Need To Consider

• For your reference, I've attained this fuel efficiency with the tyre pressure at 33 PSI (at cold temperature) on all four tyres, driving with only one passenger (apart from me who drives the vehicle), and carrying no luggage in the car. I also drive with a very lite foot and refrain from accelerating suddenly. Of course, there are plenty of other factors that can affect fuel efficiency which I have not mentioned here but I hope this tip helps the owners of the Sonet Diesel AT.

Please keep in mind that you should drive at that speed (78 KMPH) only if it is within the speed limit. If you are someone who drives at a lower speed on highway, I have no intention to encourage you to drive at a higher (78 KMPH) speed. This tip to drive at 78 KMPH is just an input from my end to help other members on the forum to burn less fuel.

Here's what BHPian harry10 had to say on the matter:

I have the D-At which is driven more than 20k km by now. To add to your informative post, I have done a lot of testing on my trips for speeds to maintain with cruise control extracting maximum fuel efficiency.

The speeds are - 63, 69, 77, 82, 95. These give the best mileage even with AC on 100%. Depending on the speed limit we can drive accordingly. Recently on a trip to Meerut I maintained 95 on cruise control and got 23 kmpl on MID for the trip.

I don't drive more than 100 even on empty expressways so no idea if above 100 will also extract max FR. However, below 100 these are the speed which are best for cruising getting best mileage.

Read BHPian comments for more insights and informarion.