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Old 29th April 2014, 14:10   #16
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Default re: Highway fuel economy less than in the city - Why?

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I think this is a typical case of petrolhead to a dieselhead.
Yes, I think that is the core issue. I have been driving petrol cars for more than 1.5 lakh kilometers and as I suspected, it will be me, who is the culprit.

Now, how do I kill my old habits is the big question for me.
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Old 29th April 2014, 14:36   #17
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Default Re: Renault Duster 85hp: High Fuel Consumption Issue

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Speed on highway : 100+

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.
I don’t think the performance kit will do you any good. There are tuning boxes available with settings like "Economy", "performance" etc. they claim that running in economy mode would give you better mileage. May be it does but it really kills the power and takes out all the fun out of driving. Trust me. I have tried it.
I drive a 1.5 diesel Ecosport and I also faced similar issue on two occasions. I got more mileage in city than on highway. Here is what I observed was the reason.

Modern cars cut the fuel supply when you let go of the accelerator. In city driving when we have attained enough speed we typically let go of the accelerator and the car covers some distance on its momentum. During this time the fuel supply is minimum, no matter which gear you are in. We tend to cover a good amount of distance in this mode if you sum it all up. On the contrary, while driving on highway, the accelerator is pressed most of the time and fuel supply is always on.

Use the techniques below to improve your highway mileage.
  • Drive in your torque band and at an RPM when your turbo is activated. (around 2000+ RPM). Modern diesel cars perform at their optimum capacity when the turbo is spooled up. The air-fuel mixture is richer in air in this state.
  • Do not press the accelerator paddle too hard. Just give it light touches whenever needed. it is called feathering. Do this to maintain your optimum RPM band.
  • Use your car's momentum whenever you can and let go of the accelerator padel on descends. but for heaven’s sake NEVER shift to neutral to cover more distance on momentum. it is too risky. I felt it is worth mentioning because I have seen people take this risk just to save some pennies.
  • if you need to pick-up speed, do that gradually. Pressing the accelerator hard will cause your car to consume more fuel.
  • Keep you air filter clean. It is very easy to do. I check mine every 5k KM.
The above works for me well and I get a mileage of 17KMPL in city as well as on highway (with AC on around 40% of the time). It drops to 15.5 or 16 if I drive with AC on throughout.

I hope this helps.
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Old 29th April 2014, 14:47   #18
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Default Re: Highway fuel economy less than in the city - Why?

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Hello All,


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?
Fuel Mileage = km/l
Speed = km/hr
Fuel burning rate = l/hr
Speed/(Fuel rate) = km.hr/(l.hr) = km/l !

The speed is always greater in highways than cities. Fuel burning rate is usually lower in highways (because you don't need high torque demands)

Do you remember your accelerator pedal position?
The more you press the greater is the fuel consumption figure.
Is it more in case of highways compared to city driving?
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Old 29th April 2014, 15:11   #19
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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.
Isn't the idle rpm 800 for diesel engines? I have been upshifting at 2000 RPM.

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2) Down shift is almost reverse of the above mentioned RPM values. But I haven't kept a close watch on that.
I downshift when RPM dips below 1500.

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3) While crawling in heavy traffic, I chose 2nd gear with more of clutch usage (some habit i am trying to change)
I am sorry but your logging the engine and frying the clutch. Please use only 1st gear for crawling traffic.

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5) Air pressure is at 29, with Nitrogen.
Is it cold tyre pressure recommended by Renault? AFAIK, it is better to fill 1-2psi more than recommended. I drive a Swift ZDi and I fill in normal air:

F - 32psi
R - 30psi

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Originally Posted by ashlyak View Post
As you said, at 100 ~ 110, I must get better kmpl. That is my worry.
Keep the speeds between 90-110 kmph will planned overtakes and no sudden acceleration. This will get you better figures in your car.

I keep getting mileage between 22-23 kmpl on average regularly but I am single most of the time.

Anurag.
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Old 29th April 2014, 15:33   #20
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Default Re: Renault Duster 85hp: High Fuel Consumption Issue

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but for heaven’s sake NEVER shift to neutral to cover more distance on momentum
In case of Duster what I observed is that shifting to Neutral cause MORE Engine Load (~50-55%) than in the correct gear w/o using the accelerator
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Old 29th April 2014, 15:42   #21
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In case of Duster what I observed is that shifting to Neutral cause MORE Engine Load (~50-55%) than in the correct gear w/o using the accelerator
How did you know there is 50-55% load?

I don't think there is 50% load on the engine in neutral gear while running.

Modern day engines cut-off fuel supply when the car is in gear but NO accelerator input is sensed hence saving fuel burnt.

Coasting with shifting to neutral and letting the car roll is risky.

Anurag.
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Old 29th April 2014, 15:48   #22
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Default Re: Highway fuel economy less than in the city - Why?

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How did you know there is 50-55% load?

I don't think there is 50% load on the engine in neutral gear while running.

Modern day engines cut-off fuel supply when the car is in gear but NO accelerator input is sensed hence saving fuel burnt.

Coasting with shifting to neutral and letting the car roll is risky.

Anurag.
I got the readings from the real time ECU OBD port data

Gliding in neutral is risky and gives more wear and tear to the clutch.
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Old 29th April 2014, 16:34   #23
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Default Re: Highway fuel economy less than in the city - Why?

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I got the readings from the real time ECU OBD port data

Gliding in neutral is risky and gives more wear and tear to the clutch.
I'm not saying that OBD was lying, but it doesn't seem to add up. I can understand that neutral may burn more fuel than appropriate gear with no acceleration, but why would the clutch have wear and tear while rotating freely in neutral?
Sorry if I am going off topic here.
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Old 29th April 2014, 18:35   #24
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Default Re: Highway fuel economy less than in the city - Why?

If you enjoy highway drives, sure the mileage will go down. I get 3.5 kmpl in highways compared to 8.5 kmpl in city and I think it is normal. Nobody likes to cruise on a highway
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Old 29th April 2014, 19:20   #25
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I get 3.5 kmpl in highways compared to 8.5 kmpl in city and I think it is normal.
Wow!

Which car do you drive that gives you 3.5 kmpl on highways and 8.5kmpl in City?

I am shocked! And I guess it is NOT normal unless your revving the engine to its nuts.

Anurag.
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Old 29th April 2014, 20:03   #26
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If you enjoy highway drives, sure the mileage will go down. I get 3.5 kmpl in highways compared to 8.5 kmpl in city and I think it is normal.
And it appeared normal to you why?
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Old 29th April 2014, 20:23   #27
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And it appeared normal to you why?
Or I guess he missed typing 1 in the 3.5 kmpl. May be meant 13.5 and 18.5 kmpl.

Anurag.
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Old 29th April 2014, 21:07   #28
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Default Re: Highway fuel economy less than in the city - Why?

1. OP has not mentioned what his actual speeds are. Hence difficult to judge / estimate possible FE for his highway speeds.

2. OP has not mentioned his method of calculating FE. Hence one more variable in this discussion

3. OP may have used MID display as the basis of his query. I just now checked with @Ampere, who also has a 85 ps Duster and it looks like the FE displayed on the MID is actually a little higher than the auto-cutoff to auto-cut off method that Ampere uses.

So OP may actually be getting a little lesser FE, though his original question would still be valid.

I also feel that 29 psi would be a little below optimal - even if it is the Renault recommended tyre pressure

Last edited by condor : 29th April 2014 at 21:13.
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Old 29th April 2014, 23:40   #29
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Default Re: Highway fuel economy less than in the city - Why?

You're sure there isn't anything wrong with the car? If you are, then it is definitely your driving style. I haven't read through the whole thread, just skimmed through it. I noticed that you mentioned at what RPMs you shift. Mate, those are too low; you'd probably be compensating by pressing the throttle even further to gain any speed. The key here is a light right foot in whichever gear. If your car has an instant mileage graph, it will be easy for you to regulate your driving style on your own. I have driven a Duster and remember getting 16 without even trying much. Hell at those speeds even my Kizashi gives 15

If you want to tune the car, I'd suggest a good remap. Try WolfMoto for switchable maps.

Cheers!
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Old 29th April 2014, 23:53   #30
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I noticed that you mentioned at what RPMs you shift. Mate, those are too low; you'd probably be compensating by pressing the throttle even further to gain any speed.
Lugging is the problem here and to compensate it - half-clutching. Both are pretty harmful and FE killers.

Anurag.
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