Experiments on my Thar AT: Fuel consumption & speed & gear selection

Please remember that my Mahindra Thar is a diesel automatic. So, what I say here pertains only to this specific variant.

BHPian tilt recently shared this with other enthusiasts.

I just did a BLR-HYD-BLR drive and did a couple of experiments since I had time.

Experiment 1: Fuel consumption

I have always been complaining that my Diesel Automatic consumes exactly as much fuel as a Petrol Thar, city or highway. Meaning the best I have ever managed was 12 on the highway, driving very very sedately and accelerating very very sedately too. I normally get anywhere between 7 and 10, with 11 being occasional and 12 being a one-time exception.

This time I decided to cruise (meaning I used cruise control) at 100 on the way to HYD and 80 on the way back. This needs a little clarification. I set the cruise control at 105-110 on the speedo; and on the "Adventure statistics" screen in the ICE display, it showed 100. Same with the 80 - it was at 84-85 on the speedo and 80 on the display.

On the way to HYD I got 13 km/l and on the way back I got 14.4 km/l.

Experiment 2: Driving speed and gear selection

Please remember my Thar is an automatic and diesel. So, what I say here pertains only to this specific variant.

When driving at 80 or 85, the car does not shift to 6th gear at all and it is not possible to force it into 6th. In fact, it is only at 90 or higher that the car shifts into 6th; and the moment the brake is applied or so, it shifts back into 5.

Remember I mentioned that I was cruising back to BLR at 80? The car was in 5th all the while, at around 1600 RPM. However, when I drive at 90, the car goes into 6th and the RPM drops to 1500.

My contention was that the fuel consumption would be lower and the economy higher at a lower RPM, and therefore (counterintuitively) I should get better economy driving faster than slower.

I wanted to see if there was any way I could force the car to be in 6th at 80 instead of sticking to 5th, so I tried something:

• I set the cruise control at 80
• I then turned off cruise control and then accelerated to 90 where the car shifted to 6th (this did not happen if cruise control was on - it stays in 5th past 90, hence the turning off cruise)
• I let go of the accelerator and hit "Resume"
• The car slowed down to 80, and wonder of wonders - the gear remained in 6th with RPM of 1400
• However, if for some reason I had to brake (meaning get out of cruise control either by braking or turning it off manually), the car will go back to 5th at 80 and stay there - I have to repeat the above steps to get back it into 6th.

Here's what BHPian ph03n!x had to say about the matter:

Using cruise anywhere you can - even at 45KMPH / 4th gives better mileage!

And yes, spot on with 80 KMPH/ 6th gear too - you can find such sweet spots for every gear. And the best mileage I have seen is (IIRC) 15.5 in 65 KMPH / 5th gear, when I was driving on undivided state highways in TN.

But your overall mileage is in line with what I've seen, 12 KMPL across 35k KM, highways getting 13 to 14 KMPL and city drives at 10 to 11 KMPL.

Here's what BHPian abirnale had to say about the matter:

Does cruise control work if you use manual mode on the stick? That way you can always set the gear to 6th, upon braking or slowing down, it will choose whatever appropriate gear for that speed and when you resume, just manually shift to 6th again. Something like on those lines?

Check out BHPian comments for more insights and information.