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Old 28th April 2014, 15:04   #1
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Default Highway fuel economy less than in the city - Why?

Hello All,

Vehicle :
I have a Duster (85) Diesel , going to be one year old and done almost 23,000 KM.


Problem :


In the city (with 100% AC on), I am getting a mileage of 14 km/l. On the highways, I am getting only 12 km/l. This is due to the high RPM and/or speed?

What I want to know :

Normally we get better mileage on highways. But my case is different with the Duster. I used to get better mileage with my other car (petrol WagonR).

Question 1 :
What would be best solution for me? Go for a tuning kit (will cost around 35k) or is there anything wrong with my driving style ?

Question 2 :
If I go for a tuning kit, and I put that on performance mode, will it consume more diesel and reduce my mileage further ?

Question 3:
Are there any other technical issues, which I should investigate ?

Question 4 :
With my WagonR, I used to get better mileage on the highway, but not with Duster. Is there anything wrong with my driving style? If so, how do I correct it?

Thanks

Last edited by GTO : 29th April 2014 at 14:30. Reason: Typos
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Old 28th April 2014, 15:09   #2
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Default re: Highway fuel economy less than in the city - Why?

There's something very wrong here.
Whats your shift pattern on the highway, or even generally?
What RPMs do you shift at etc etc.
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Old 28th April 2014, 15:20   #3
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Default re: Highway fuel economy less than in the city - Why?

Too little info provided here!

On highways...

1) What speeds do you do
2) Load - Pax? Luggage?
3) What highways
4) Tyre pressure, tried Nitrogen?
5) Did you check for clutch slippage? RPM Meter will reveal?
6) Is this FE from MID or tank-full-tank-full?
7) Give your car to another good friend and do a 80ish run on open highway to maddur (I see you from blore) and back on a less traffic time and compare the results.
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Old 28th April 2014, 15:55   #4
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Default re: Highway fuel economy less than in the city - Why?

Perhaps the speed and revving would be the culprits. If you are enjoying the macho acceleration through the gears to outrun other vehicles, curb it and observe the difference.

Last edited by rajeev k : 28th April 2014 at 16:20.
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Old 28th April 2014, 16:11   #5
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Speed on highway : 100+

RPM touching 2000, at the speed of 80km/hr is noticed. Sorry, I don't remember the RPM at 100+. Will keep a watch and update.

Load : Normal load. 2 People and 3 or 4 bags, normally.

Highways : NICE Road Bangalore, Mysore Bangalore Road, Bangalore Hassan, Bangalore Selam etc.

Tyre Pressure : 29 (as recommended by Renault)

Clutch slippage : Got this checked during last service and no issues were found.

FE at Mid and full tank : are almost same.

Giving car to friend : Tried that. Reading shows that his driving style is giving better mileage than mine. But lesser than the city mileage.

Rajeev : Yes, That is my first doubt. The happiness of driving duster makes me push him harder and harder. That is why I am considering a performance kit. May be that can give me same performance, without too much of fuel burning. I am not sure. That is one thing, that I want to know.

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Last edited by GTO : 29th April 2014 at 14:31. Reason: See note in post
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Old 28th April 2014, 16:30   #6
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Default re: Highway fuel economy less than in the city - Why?

ashlyak, If you tell us more about the driving style it would be easier for us to give you a clear reply.
  • What's your driving style?
  • At what RPM do you upshift and downshift?
  • Do you keep the accelerator pressed at 100% all the time?
  • Once you reach your desired speed, do you maintain the speed or you keep varying it? How hard do you accelerate for normal overtaking maneuver or after some unexpected slowdown?

I have driven the Duster 85hp for a good amount of distance on highways. Even when driving at speed on Rajasthan's highways, the fully loaded Duster returned FE figures in range of 17-18kpl.
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Old 28th April 2014, 16:39   #7
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Default re: Highway fuel economy less than in the city - Why?

Driving Style : Well, I think the best example would be to mention about the mileage I used to get on my 2005 model Wagon R. I used to get a mileage of 16 km/l on the same highways. Based on my observations, and feedback from a friend, I shift the gears at lower RPMs.

And yes, I keep touching the accelerator most of the time. But, once I reach a comfortable speed, I give soft touches to maintain the speed. Not overkill.

During over taking and unexpected slowdowns, I go slightly hard on the accelerator, to maintain the average speed.

Last edited by GTO : 29th April 2014 at 14:32. Reason: Typos
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Old 28th April 2014, 17:26   #8
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Default re: Highway fuel economy less than in the city - Why?

Ashlyak,

Answer these specific questions:

1. What ____RPM do you upshift at?
2. What ____RPM do you downshift at?

While crawling (in 2-3 kmph pace traffic) what gear do you choose?
1st gear with minimal clutch use?
OR
2nd gear with too much clutch use/slippage?

Do you live in a dusty environment?
When was your last service done? Are you sure air filter was cleaned/changed in that service?

When you go to check/fill air in tyres, how much pressure do the tyres show?
Are they just 1 or 2 points lower than 29 psi?
OR
Are they even below 25~26psi?

One more important thing:
(Since I noticed you said NICE road & some other good roads)
If you tend to drive at really high speeds -you "will" see bad figures as your FE.
Even at 100~110 - I believe you can expect 17~18 kmpl (@30psi tyre pressure ).
I am sure - at 140~150 you will see a LOT WORSE FE.
The FE could even be as low as you are getting.
(These speeds aren't the intent of 85PS model, and aren't safe either)

Not sure what figures you are doing, since both the above mentioned ranges are 100+

Thanks,

Ace.

Last edited by driverace : 28th April 2014 at 17:46.
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Old 29th April 2014, 10:17   #9
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Default re: Highway fuel economy less than in the city - Why?

Hello Ace,

Thank you !

1) I move from 1st to 2nd at around 750 or 800 RPM. Then to third at 1000 RPM. Third to 4th happens sometimes at 1000 RPM, and some time bit above that. Moving to 5th is around 1500 RPM.

2) Down shift is almost reverse of the above mentioned RPM values. But I haven't kept a close watch on that.

3) While crawling in heavy traffic, I chose 2nd gear with more of clutch usage (some habit i am trying to change.)

4) No, I don't live in a dusty environment and the air filter was changed two months back.

5) Air pressure is at 29, with Nitrogen.

As you said, at 100 ~ 110, I must get better kmpl. That is my worry.

I have OBD which works via Bluetooth. If you want any specific reading, I can collect that and share.

Last edited by GTO : 29th April 2014 at 14:34. Reason: Typos
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Old 29th April 2014, 10:22   #10
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Default re: Highway fuel economy less than in the city - Why?

Quote:
Originally Posted by ashlyak View Post
Hello Ace,

Thanks you !

1) I move from 1st to 2nd at around 750 or 800 RPM. Then to third at 1000 RPM. Third to 4th happens sometimes at 1000 RPM, and some time bit above that. Moving to 5th is around 1500 RPM.

This doesnt sound right, unless the mill in the renault is drastically diffferent.
Comparably, in my tucson, I shift from 1st at around 1.9, then 2.5, and the rest between 2.5-3.
This is sprightly for her, but i still pull better figures than what youre getting in a car about 1L kms and 7 years younger.

I think you need to revisit this style.
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Old 29th April 2014, 11:22   #11
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Default re: Highway fuel economy less than in the city - Why?

Quote:
Originally Posted by ashlyak View Post

1) I move from 1st to 2nd at around 750 or 800 RPM. Then to third at 1000 RPM. Third to 4th happens sometimes at 1000 RPM, and some time bit above that. Moving to 5th is around 1500 RPM.
@Ashlyak, my friend that sound like you are lugging the engine. shifts are best done at the mid range of the peak torque range.
Your car produces 200 Nm @ 1900 RPM, so the best shift point is at around 1750 rpm. as you progress in gear you can move the shift point between 1500 to 2000 rpm depending on the load in your car.
You might very well know that most of the fuel is consumed to attain speed (acceleration) so if you dont allow the engine to reach its torque band while accelerating you'll get the proper efficiency the engine is meant to provide.

In town the story is different as you wont be pushing the car to attain high speeds as speeds are limited.

Before you start practicing this shift pattern there is something you might want to and need to do for your car.
Find a nice stretch of open road and floor it. Go through all the gears, ok maybe until 3rd but shift only near the redline or maybe at 4000rpm, trust me the Renault engine is capable of far more stress so its only like churning butter for your car.
You'll attain very high speeds while doing this so please take caution.
This will not only put a smile across your face but most importantly it will clear any blocks in the injectors fuel rails and clear any excess carbon deposits from the exhaust.
Just like the air filter, the exhaust also needs to be clear for the engine to perform at an optimal level.
BUT PLEASE TAKE CAUTION WHILE DOING SO, REMEMBER YOU NEED A NICE STRETCH OF OPEN ROAD WITH NO OR SMOOTH CORNERS.
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Old 29th April 2014, 11:33   #12
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Default re: Highway fuel economy less than in the city - Why?

- The FE is low to start with.
- And its getting reduced because of higher speeds (100+) on the highway.

One check can be :

- Try a speed of 60-80 on the highway in 5th gear.
- Then see if the FE at least matches to what the OP gets in city or goes above.

If he can establish the earlier part, then we know for sure that FE seen is low to begin with and the driving style aspect can be isolated.

Last edited by ampere : 29th April 2014 at 11:36.
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Old 29th April 2014, 11:40   #13
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Default re: Highway fuel economy less than in the city - Why?

Thank you every one. But at 2000 RPM, the car is really roaring ! Let me try today after noon or evening, but not sure, if I can move from 1st to 2nd gear at 2000 RPM. Will check and update. Normally, when I cruise at 2000 RPM, the speed will be between 80 km/h and 100 km/hr
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Old 29th April 2014, 11:55   #14
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Default re: Highway fuel economy less than in the city - Why?

Boxy design
2500+ rpm diesel engine running out of its torque band
100kmph+ speed - No wonder you get less mileage.

In Safari - 100kmph type of runs - 12.5 - 13kmpl
60-70kmph type runs = 16kmpl
Chandigarh type city(or what chd was 10 years ago) - 14kmpl
Stop and go - 10-11kmpl

Drive in the sweet spot 2000-2200 rpm and then see your mileage soar.
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Old 29th April 2014, 13:03   #15
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Default re: Highway fuel economy less than in the city - Why?

I think this is a typical case of petrolhead to a dieselhead. I am having an 85PS(O) and using in Bangalore and I am getting far better mileage. Following are my observations:

- Change the driving style, for the 1st and 2nd gears shift ~1500-2000 and the rest slightly above 2000rpm.

- To get better mileage, always use pulse and glide driving technique so that the vehicle will be moving continuously at the desired speed but with less fuel. You can do the same even at very high speeds also.

- Shifting will reduce the mileage, but at the same time unlike petrol cars never lug the vehicle. Slot in the correct gear and reach the correct rpm asap and move to the high gears. Also its a myth that only 5th gear or top gear gives the best mileage, we can get the same using 4th gear also from my experience in ORR Bangalore traffic as the rpm required for 5th will force you to downshift frequently depending on the traffic, instead maintain the 4th gear throughout will have less gear change but with good speeds and I didnt see any drop in mileage due to this.

- Use engine breaking as much as possible, I have seen people using brakes unnecessarily on seeing a small change infront and forced to shift down in most of the cases, instead release the accelerator for a while, the transmission will reduce the speed and depending on the situation apply brakes if necessary, thereby you will avoid any down shifts and save the brake pads too.
I have seen people changing brakepads at 10K service!!!.

Note: None of the performance tuning will give you better mileage unless you drive according to the vehicle.

Last edited by ::CMS:: : 29th April 2014 at 13:16.
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