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Old 29th June 2011, 07:41   #1
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Default How much fuel is consumed on engine start?

Hi,

I wanted to know how much fuel is consumed each time we start our vehicles. I'm talking about petrol vehicles in range of 1200 cc to 1800 cc. Though it's advised that to save fuel whenever we have to stop for more than 2 minutes we should switch our engines off which should translate to around 30 to 40 ml of petrol consumed on each start.

I tried searching answer to it but couldn't find one.
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Old 29th June 2011, 10:24   #2
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Default Re: Fuel Consumed During Start

I guess the stopping interval has come down to about 30 seconds, so if you are going to stop for more than 30 seconds, you should ideally switch off your engine.

You should also throw into the equation the amount of fuel that will be burnt if the engine idles for 30 seconds.

So yes, I would like to know some approximate figures too.
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Old 29th June 2011, 10:37   #3
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Default Re: Fuel Consumed During Start

Start-stop system - Wikipedia, the free encyclopedia


toyota, doing this in 70's used 1.5 seconds!
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Old 29th June 2011, 11:25   #4
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Default Re: Fuel Consumed During Start

This link provides some interesting info:

Fuel economy-maximizing behaviors - Wikipedia, the free encyclopedia
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Old 29th June 2011, 13:11   #5
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Default Re: Fuel Consumed During Start

In general the rule is to switch off the engine if one has to wait for over 60 seconds (timers at red light are very beneficial for this purpose). I don't think that it will be sensible to switch off the engine for 20-40 seconds stop. The reason is that first it causes starter to wear unnecessarily, secondly it consumes battery power and finally starting the engine sometimes consumes more oil than idling for 20-30 seconds as many of you must have noted that when we start the car, it idles at much higher RPM and then settles. This will ultimately consume more fuel.

Last edited by bluevolt : 29th June 2011 at 13:13.
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Old 29th June 2011, 14:07   #6
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Default Re: Fuel Consumed During Start

The fuel consumed itself during start up has to be very minimal. But the engine draws substantial power from the battery, which has to get charged back to that level by burning fuel. So probably it is this fuel quantity you are interested in knowing.
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Old 29th June 2011, 14:12   #7
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Default Re: Fuel Consumed During Start

Quote:
Originally Posted by bluevolt View Post
... as many of you must have noted that when we start the car, it idles at much higher RPM and then settles. This will ultimately consume more fuel.
You are describing a cold start, where the engine is cranked in the morning after it has rested for a whole night. What about a situation where I have driven for half an hour and then stop at a light and switch off the engine? It has already reached its operating temperature. I don't think it would drink any more fuel than idling. If the engine took two seconds to crank I would equate it with two seconds of idling. So if I switch off the engine and then start in about ten seconds, I have actually saved a few seconds of idling.

With modern MPFI engines it's hard to conceive the ECU would be injecting more fuel than necessary into the chamber.

Also the statement on starter motors: I have yet to see anyone actually giving proof that the starter motor is affected due to frequent starts and stops. I have been switching off my engine even in bumper to bumper traffic, where I have to move ahead a couple of feet and then wait for about 30-40 seconds before crawling another couple of feet, for a total duration of about 200 meters, for many years. On both my cars, M800 and Santro I have never faced any problems with starter motors. And both were old.
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Old 29th June 2011, 14:43   #8
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Default Re: Fuel Consumed During Start

Perhaps the fuel consumed during starting at signals (not cold starts) would differ between diesel and petrol mills?

Also, does it make any difference if the air con is kept switched on while stopping/ starting at signals? I am not aware of the effect this has on FE.
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Old 29th June 2011, 15:09   #9
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Default Re: Fuel Consumed During Start

With Scangauge Fuel consumed per hour during ideling is between 0.8 lts to 1.2 lts depending on weather AC is on or not. Which means approx 20ml per minute.
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Old 29th June 2011, 15:16   #10
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Default Re: Fuel Consumed During Start

Which car did you measure it on?
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Old 29th June 2011, 15:24   #11
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Default Re: Fuel Consumed During Start

Quote:
Originally Posted by saurabhkum View Post
With Scangauge Fuel consumed per hour during ideling is between 0.8 lts to 1.2 lts depending on weather AC is on or not. Which means approx 20ml per minute.
This seems to be first hand data. Is it possible for you to elaborate the observations with Scangauge? Like which car, conditions etc.
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Old 29th June 2011, 15:28   #12
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Default Re: Fuel Consumed During Start

I do the switch off only if I have more than a minute and am not using AC. Which is only for a couple of months in Chennai weather! I think the power drawn and the fuel consumed when we start after 60 seconds negate any gains made during the stop.
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Old 29th June 2011, 15:28   #13
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Default Re: Fuel Consumed During Start

Sorry the car is Hyundai Accent 1.5lts
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Old 29th June 2011, 15:35   #14
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Default Re: Fuel Consumed During Start

Quote:
Originally Posted by saurabhkum View Post
Sorry the car is Hyundai Accent 1.5lts
Is your Accent fitted with a Scangauge?

Didnt understand why are you sorry about the Accent.
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Old 29th June 2011, 15:41   #15
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Default Re: Fuel Consumed During Start

Good topic. Common sense would suggest increased fuel consumption during cold start and nominal consumption during startup of an engine that has reached optimal temperature. Starting torque required for the engine rotor would cause some amount of battery drop which in turn would consume extra fuel to recharge. As a thumb rule, anything above 30 secs at a red light calls for turning off the engine. Sadly, most traffic signals here do not have timers. So you have to guess if you should turn off the engine or let it idle.
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