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Old 1st October 2011, 00:05   #16
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Default Re: The curious case of highly varying FE during city & highway driving

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The Ikon manual has a nice graph which depicts FE in different gears. Unfortunately I dont have the manual (and the car) now. Is it possible to post the graph here?
Ask away dot!

The curious case of highly varying FE during city & highway driving-fuel.jpg
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Old 1st October 2011, 09:13   #17
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Default Re: The curious case of highly varying FE during city & highway driving

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Ask away dot!
Thanks a ton dhanusus. I owe you one! (BTW, how did you scan the page at 12 am? Amazing.)

I think this graph nicely answers many of the questions that are being discussed here. In city traffic where we usually shuffle within 1-2-3 gears, the FE is naturally and expectedly less.
Further, at high speeds FE increases with speed irrespective of gear position.

Now why some cars have a wide range in city an highway FE depends on torque and power bands of that car at low rpm.

Lets also remember that FE = 0 at idle. So more time at crawling traffic, more horrible the number as the weighted average will be closer to lower values than higher.

Last edited by dot : 1st October 2011 at 09:18.
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Old 1st October 2011, 14:13   #18
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Default Re: The curious case of highly varying FE during city & highway driving

I do not know how he scanned, but for most small area scans I use my mobile phone camera! Mighty useful, especially in field when you have to send a drawing over mail. Of course the MP matters on how much clarity you will get, or looking the other way, how much you can "scan" in one frame.
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Old 1st October 2011, 15:27   #19
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Default Re: The curious case of highly varying FE during city & highway driving

A very rudimentary way of explaining is that in a city drive your engine is running for say 1 hr covering 15 km , where as in highway, you will cover around 80 km. So your fuel efficiency should be theoretically 5 times more. Factor in various factors like idling (consumes lesser power), lesser wind drag at lower speeds( air drag contributes more to traction effort than any other factor ) you end up with 30-40% more mileage. So the cars (hatchbacks) are tuned for city driving than highway driving.
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Old 1st October 2011, 22:45   #20
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Default Re: The curious case of highly varying FE during city & highway driving

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I do not know how he scanned, but for most small area scans I use my mobile phone camera!
OT:
Shows that I am a pretty techy challenged person. It was indeed a photograph. Thanks for showing me the (flash) light!
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Old 2nd October 2011, 14:58   #21
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Default Re: The curious case of highly varying FE during city & highway driving

Noticed something peculiar today.

Generally when I drive in the city, the engine temp. needle is right in the centre of the guage. On the recent highway drive, the engine temp. needle was stuck at around 1/4th.

While on a city drive today, the needle was at 1/2 as usual and on a particular 3km stretch where I was cruising at 60 km/hr without interruption, the needle actually sunk back to 1/4.

I don't know if it is only now that I'm "noticing" it or this is unusual. Does this happen on other cars as well?

Also, any one with technical specs on the Corsa's gearing pattern?
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Old 2nd October 2011, 15:18   #22
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Default Re: The curious case of highly varying FE during city & highway driving

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Does this happen on other cars as well?
As I mentioned before, while on the highway, the engine runs cooler, due to increased cooling from the ram air.

One car, in which there is some real movement of the needle during city and highway runs is the Indica DLS. For best FE, we usually try to keep the needle as low as possible. Which also means less engine load.
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4. While on the highway, the engine runs much cooler.
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Old 2nd October 2011, 22:05   #23
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Default Re: The curious case of highly varying FE during city & highway driving

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Originally Posted by libranof1987 View Post
Noticed something peculiar today.

Generally when I drive in the city, the engine temp. needle is right in the centre of the guage. On the recent highway drive, the engine temp. needle was stuck at around 1/4th.

Does this happen on other cars as well?
Frankly, I have never seen this phenomenon in any of my recent cars: Altima - 2.4L, Civic - 1.8L, Ikon - 1.3L, Santro - 1.1L. The reason I mentioned the engine capacities is that irrespective of engine volume in these cars, engine temp needle would reach one particular value in any type of traffic condition and would not change.

Last edited by dot : 2nd October 2011 at 22:06.
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Old 3rd October 2011, 11:31   #24
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Default Re: The curious case of highly varying FE during city & highway driving

If your cooling system is designed properly and all the components are working, the the engine should reach its operating temparature (around 100 degrees), fast and stay there irrespective of the load and ambient temperature. Any excessive heat generated should be dissipated by the radiator. If the climate is cold, then the fan stops and later on the thermostat in the block limits water going to the radiator so that the engine is running hot. In short the engine cooling system should maintain a constant temperature.

So when ever you notice that the temperature needle is varying with load, there is a need for better control. Rather than using the temperature needle as a load indicator, use it to check if the operating temperature is reached, or there is some problem in the cooling system indicated by high temperature readings. Contrary to popular belief engine running cooler than normal is going to decrease FE and performance.
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Old 3rd October 2011, 12:06   #25
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Default Re: The curious case of highly varying FE during city & highway driving

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Originally Posted by libranof1987 View Post
... Generally when I drive in the city, the engine temp. needle is right in the centre of the guage. On the recent highway drive, the engine temp. needle was stuck at around 1/4th. ...
That's pretty normal, nothing peculiar. Start-stop driving and more idling than cruising will cause the water temperature to increase, especially in warm/hot weather. @dhanushs gave the correct pointer - increased forced cooling while driving >50Kmph.

BTW, were the mileage figures you quoted from actual calculation (almost - tank top-up method for example) or from the MFD? If MFD, you are getting the short term consumption figure. If for any reason you are forced to do start-stop driving on a highway (happens! Anyone have experience of 101 in the Bay Area?) you will get higher consumption figures like in start-stop driving in city.

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Originally Posted by dhanushs View Post
... One car, in which there is some real movement of the needle during city and highway runs is the Indica DLS. ...
True, that! Even others of the same family like the V2 etc. My sister usually makes a panic call to me from Delhi if the needle crosses 1/2. She can write pages on the cooling system problems she has had with her V2 over the years, not the least due to the hathoda-chhaap mechanics at TASS in Delhi.
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Old 3rd October 2011, 12:15   #26
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Default Re: The curious case of highly varying FE during city & highway driving

One more point to be added: When we measure the FE in city, we measure it over a period - say over a week. Consider the number of times we cold start. A lot of fuel is wasted there. Also, there could be leakages in the fuel tank/lines (however minor they are) which would also make a difference due to the extended time period (a week or so) over which we measure FE. In a long drive, we measure it within a day
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