‘Diesel Automatic Cars Aren’t Fuel Efficient’: Myth Debunked!
For years, India has loved diesel cars. Their impressive fuel efficiency figures made many people equate diesel with 'mileage'. Discussions around the real-world fuel efficiencies of diesel automatic cars and SUVs are spooling up online. The statement 'Diesel cars with torque converter automatic transmissions are NOT fuel efficient’- echoes in most car conversations! This is, in fact, ridiculously vague and largely incorrect, at least in the time we live in. This article will explain why.
A video shared on Instagram by Vikas Yogi, an automotive content creator, has sparked the latest round of discussions on this topic. He starts it by making a bold statement- ‘Diesel automatics are not fuel-efficient at all’ and further substantiates it by citing examples of several models- Kia Seltos, Syros, Hyundai Venue, Tata Sierra, and so on. He says that all of these diesel automatics are ‘not fuel efficient’.
In the video, we see the host driving the new Kia Seltos. He talks about how the car’s cluster is displaying a mileage of just 11+ kpl and how it dropped to around 9 kpl in tight city traffic. In his closing remarks, Yogi says that if one wants to maximise fuel efficiency, he/she must buy a diesel manual. Quite convincing, right? Now watch it another time, with a more critical and logic-based eye, and you’ll see a lot of holes in the narrative.
It doesn’t talk about driving style, number of occupants, and other factors that have direct impacts on the real-world mileage. He is seen driving on a smooth, well-paved road. The screen shows the current trip mileage as 11.5 kpl, measured over a distance of 5.1 km. Here comes the tricky part. We don’t know if the roads were so good throughout the journey.
‘Current trip mileage’ is not an instantaneous measurement; it is calculated over a certain distance and at regular intervals. So, if he has been driving through poor roads previously, with aggressive throttle inputs or in bumper-to-bumper traffic, the numbers would drop drastically and would only recover gradually. The math behind this is slightly complex. We don’t claim this to be a fault in the narrative, but it is definitely confusing!
More importantly, this video generalises things. ‘Diesel automatics are not fuel-efficient at all’ is a statement that implies that a car with a modern diesel engine and a new-age torque converter automatic transmission (say an 8AT) and an older generation diesel engine and an older transmission (say a 4AT) will both be bad with fuel efficiency.
We understand how such hooks can increase viewership and get the conversation going by aligning users on either side of the debate. In the more serious picture, they lead people to believe that the stated argument is completely correct! Ideally, the host should have phrased it ‘Diesel automatic cars aren’t as fuel efficient as diesel manuals’.
Let’s be clear and honest. A diesel engine mated to a torque converter automatic transmission will not be as efficient as the same paired with a manual gearbox.
Conventional automatic transmissions (which we usually denote with ‘AT’) don’t have a ‘clutch’ that disconnects the drive. An AT transmission uses a device called ‘torque converter’ instead. In olden times, torque converters used to cause large power wastage, eventually leading to low mileage. In the past few decades, conventional automatic gearboxes and their tech (including torque converters) have evolved a lot.
They have become more efficient and advanced. Many of their past issues and vulnerabilities have been ironed out. Today, the mileage gap between diesel automatics and diesel manuals has reduced drastically. Generally, fuel efficiency increases as the number of gears increase and with newer generations or iterations of the transmission setups.
From a customer perspective, diesel automatic variants of most cars and SUVs make a lot of sense. They are good to drive in the city and on highways and are quite fuel-efficient too, if driven the right way. In the hot mid-size SUV segment, almost all contenders offer diesel automatics (diesel engine+ torque converter ATs). Don’t hesitate to buy these, if you want to. If chosen right and used well, they won’t burn a hole in your pocket.
Don’t buy a diesel automatic if mileage is the only thing that you care about. Diesel manual variants will have slightly higher mileage figures. This doesn’t really mean that automatics return pathetic fuel efficiency figures. This is where this article differs sharply from the video content.
At Cartoq, we daily drive at least two diesel automatic SUVs. I have been driving a Seltos diesel AT (the same engine and transmission as the vehicle in the video) for the past 1.5 years.
30,000 kms down the line, I can confidently say that the actual mileage returned by this powertrain depends on where and how you drive. Even the fuel we use plays a role in shaping the overall fuel efficiency. I usually recommend IndianOil’s XtraGreen premium diesel, which has a high Cetane number, for anyone looking to maximise mileage.
The 1.5L diesel engine- 6AT combination on the Seltos, impresses with its fuel efficiency. The torque converter in this case is quite impressive and has efficient.
The SUV doesn’t, however, excite us with outright performance, but packs enough punch to keep the driver engaged. The 6-speed automatic transmission syncs well with this engine and feels good to drive. More importantly, it returns good fuel efficiency figures.
On a long 700 km highway trip, I was able to achieve up to 25.5 kpl. In regular city traffic, the car usually returns between 11 and 14 kpl. It has never dropped below 10 kpl so far.
On regular drives, it returns around 13-16 kpl. On highways, the figures usually rank in the 18-20 kpl bracket. The hack here is to maintain the right rpm. Keep the engine in its sweet spot. And finally, rely on tank-to-tank or refill-to-refill data for calculating the fuel efficiency.