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Old 31st August 2010, 20:11   #16
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Originally Posted by xbox360 View Post
I actually thought about this quite a while ago and do the following to get the best of both whenever prossible -- I have my windows up and the AC off, and simply I set the blower at high speed.
Oh yes, I too do that and during rains & winter, I think its the most fuel efficient option.
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Old 31st August 2010, 20:38   #17
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Whenever I start driving, I start with windows down and blowers on to drive the stale air out. Then I roll up the windows after 2-3 minutes and turn on the AC.
I only drive with windows down/sunroof open if it has just rained (no dust and pollution) , and the road is clear (no truck to spew poison gas).
I believe clean interiors + no pollution + comfortable cooling is a worthy trade off for 1-2 kmpl less FE. More so in Kolkata. Maybe in NorthEast or Himalayas the situation is different.
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Old 31st August 2010, 20:45   #18
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For me its like this:
Dusty,hot or warm,sunny day, smoky roads with malodorous exhaust gases: Windows rolled up, AC on!
Monsoon weather, no rains, no dust,cloudy, cool: Windows down, AC off.
Dusty winter weather, cool: Again windows rolled up, AC used in the warm and circulation mode.

So summing up, dusty, polluted air or warm weather always use AC.
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Old 31st August 2010, 21:04   #19
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I almost always drive without AC, except on long drives or when with family and kids start sweating.

apart from the FE, I believe in avoiding too much comfort. Once in a while sweat glands need a workout too. weather in cincinnati is not that bad either.

I have found out that on a hot day, opening windows slightly makes it better than windows fully open. I think it's because 1) it doesn't rob you of your moisture quickly. 2) when air enters the car at pressure and expands, it loses its internal energy (temperature). Otherwise i just passes thru.

on highways aboe 65mph it makes sense to use the ac with windows up. it gets very noisy and windy inside.
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Old 31st August 2010, 23:15   #20
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Within city its Windows at 50% and blower set to 2speed.
On highway its definetly AC !!! unless the weather is extremely beautiful !!
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Old 1st September 2010, 13:39   #21
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afaik, in turbo cars, the turbo kicks in based on rpm and load, the difference in FE with or without ac should not be much even in city driving.
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Old 1st September 2010, 14:59   #22
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Highway driving : windows fully rolled up and AC on (winds does not destabilise the car at high speeds)

City driving + comfortable weather: both front window rolled up 95% and AC off (maintains ventilation + aero profile maintained to large extent)

City driving + hot weather : windows fully rolled up and AC on and thank God for giving me AC. (who cares about aerodynamic of the car)

Any which way the difference in fuel efficency (with or without AC) in a diesel car is not that much.
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Old 2nd September 2010, 19:25   #23
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Windows mostly closed until and unless the weather is good and pollution non existent, that is the hills. In hot and / or humid weather AC on. In winters AC off, but windows closed.

I have noticed that the best indicator of extra power used by AC is to try switching it off and note if the car goes faster. In general above 60 in both my Esteem and my K10 the power loss with AC, beyond 60 is insignificant.

My reading is that the AC consumes constant power, while the vehicle consumes power in proportion to the speed. Hence the point where the AC power is less than 5% of the vehicle power is where the power consumed by AC is negligible. This is borne out by my recent tests where I drove my new K10 in stop-and-go traffic with AC on, and the consumption was 12+. The next tankful I am driving on open roads and the consumption seems to be near 17 mark.
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Old 9th December 2010, 19:55   #24
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Default Re: Windows down or A/C on -- which is more fuel-efficient?

If I want to enjoy the scenery/ weather, I use my bike. for me, one of the main reasons for driving a car on congested city roads is to keep out the noise/ dirt pollution.
it would be ideal if a car were built in such a way that you could split them into two motorbikes if required. Or if you could have a car that could fit a motorbike at its back (like the bicycle racks). One could just drive till a point of no pollution (read low pollution!) and then take off on the motorbike

Last edited by selfdrive : 9th December 2010 at 20:00.
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Old 9th December 2010, 20:51   #25
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Default Re: Windows down or A/C on -- which is more fuel-efficient?

Driving in Bangalore more often than not means stuck in traffic jams every now and then; you end up idling much more than you actually move! Hence, in this scenario, the FE diff between driving with a/c and windows down is quite significant.

Unless of course when there are smoke-generous 2-wheelers and trucks, there's no choice but to let the a/c do its job.

More so, I have found the FE difference in a/c on and windows down terribly huge in my Corsa; it come to at least 3 km/l. This implies I can't indulge in the luxury every now and then!
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Old 10th December 2010, 02:35   #26
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Default Re: Windows down or A/C on -- which is more fuel-efficient?

I keep my windows up, and doors locked all the time. Switch OFF the A/C only when its too cold.

Well, I do roll down my windows sometimes, and its when I feel like revving her up and listen to the 'wrroom', say, up the ghats. .

All said, I get a city efficiency of 13km/l and a highway efficiency of around 17km/l. Not bad, considering a sedan with decent build.

Somehow, I feel that the penny earned by windows down is just not worth it.
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Old 10th December 2010, 06:08   #27
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Default Re: Windows down or A/C on -- which is more fuel-efficient?

I always keep my windows rolled up and whenever i feel too cold then i would increase the temperature of my AC, as i have ACC its very convenient to maintain opt temperature that you need. Added to this, you need not clean your interiors often if you keep you windows rolled up. Tiredness would be more if you drive with windows down.

I do role my windows down when I am in hill station to feel some greenery and fresh air.
I am getting a descent efficiency of 10km/l for city drive and 13.5km/l for highway drive.
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Old 10th December 2010, 09:26   #28
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Default Re: Windows down or A/C on -- which is more fuel-efficient?

I have window rain-guards installed.

In city non-traffic hours, windows are half rolled down. For visibility and some air.

On highway, I keep only 1/2-1 inch of window open (raining or not). Nice cool winds come in and rain doesnt!

However over speeds of 90kmph, I close all windows and start blower (speed 2 or 3) in fresh-air mode.
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Old 10th December 2010, 09:54   #29
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Default Re: Windows down or A/C on -- which is more fuel-efficient?

For town driving Windows Down, and on the Highway AC On. Wind resistance goes up as the fourth power of the speed. So pottering about town at low speed the additional drag due to open windows is lower than the juice taken by the AC, on the highway closed windows with a lower drag are more efficient.
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Old 10th December 2010, 10:35   #30
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Default Re: Windows down or A/C on -- which is more fuel-efficient?

I am interested to know, what would you generally set the speed of AC blower to.
In my Santro Xing, i feel it very pleasant when i set the blower to 2 and keep alternating it to 1, when i find it little cold
Will keep the blower between 1 and 2 improve the FE than running it at full blower (4)
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