Citigo stop/start economy

[Emil]

My memory serves well. Doesn't matter if the heater is switched up onto screen or not, it stops anyway. Engine temperature 60c and ambition temperature 0.5c.

[Fusioncrust123]

Yep, mine stop/starts fine with defrost setting too? Had it a few times when I've parked up waiting for the wife or daughter and after a bit the engine restarts automatically when I've not touched the clutch or brake. So assume as listed above that the battery use must have triggered it. Great system really and probably more complex than we realise. No issues with mine at all :-)

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[alianmac]

As a long standing member of the Institue of Advanced Motorists (IAM) who has been pondering whether Stop-Start is a good thing or not since I bought my 75PS GreenTech, I thought that I would ask for their advice on this matter. Below is my query - posted on 16 April - followed by the response that I received this afternoon. Seems pretty conclusive to me. I can't think of any reason for the IAM or the AAA to big up such systems if they are not what they claim to be.

 

================================================================

 

Hi,

 

This email is a follow up to a response I made to a recent IAM questionnaire. In it, I said that I would appreciate advice on how to make best use of some of the more advanced technology in modern cars.

 

It relates to the purpose of the stop start system that is fitted to many cars under branding such as "BlueMotion", "GreenTech", "Efficient Dynamics", etc. These are the systems that automatically shut down the engine of the car when it is stationary and the driver removes their foot from the clutch pedal. They then restart the engine when the clutch pedal is depressed again.

 

There seems to be an assumption by the manufacturers that this happening automatically is "a good thing" and the driver should just go along with it. However, I am not so sure. I have been looking for a more in-depth analysis of these systems, what they actually achieve and what the best use of the actually is. I have not been able to find anything other than opinions expressed in discussion groups.

 

I wondered if you had access to any analysis or research that shows what the benefits are? Reduced fuel consumption, improvements in air quality, allowing vehicles to qualify for lower tax bands/pass stringent emissions tests are the ones that come to my mind. Also I wondered if the IAM or any other independent and responsible driving organisation had done any real world testing to see how these systems work in real life and to develop guidelines for how to use them when driving in everyday traffic. For example, when in a traffic queue that is exhibiting stop start progress, should one stop and wait, rather than crawl gradually forward? Such behaviour runs the risk of irritating drivers behind. Likewise, an observant driver can see from other traffic lights and how long the lights affecting them have been from red that they might have a very short wait (or conversely a very long wait) before they will be allowed to progress. So what is the period that the engine has to be switched off before any cost (amount of fuel or air quality) has been exceeded?

 

Thank you in advance for any assistance that you might be able to give me.

 

===========================================================

 

Thank you for your query.

 

These automatic stop-start systems are becoming almost universal for cars with piston engines, because it is relatively straightforward for manufacturers to do and it has significant advantages for both fuel economy (and thereby lower CO2 emissions) and for urban air quality.  You raise some interesting questions which I’ll answer more or less in order, but first, I’m only going to deal with stop-start systems and that’s the name I’ll use.  Branding such as “Blue Motion” or “Efficient dynamics” usually includes some other efficiency measures as well.

 

The manufacturers claim fuel saving of around 5% for typical drivers and typical journeys.  The IAM does not carry out testing of this sort, but the AAA (Automobile Association of America) did conduct independent tests on three cars in 2014 and found they used 5% to 7% less fuel when the system was enabled, which corroborates the manufacturers’ claims.  Urban air quality is probably an even bigger winner, because most traffic jams are in towns, where the air quality problem is worst.  NOx and particulate matter (soot) from diesel engines are serious health hazards and turning the engine off when not needed means they fall to zero.

 

Many people have asked how long the engine has to be turned off to actually save any fuel.  This is because there was a belief that it takes some extra fuel to get the engine started again, recharge the battery and so on.  While this is true for a cold engine started after the car has been left overnight, it is not the case for stop-start systems.

 

When you switch off the ignition and leave a car, you turn off the computers controlling the engine.  When you return and start the engine, it turns over at least twice before starting, because the computer needs to work out the crankshaft position before injecting fuel and firing a spark plug (on petrol engines).  Only after two complete turns does it “know” which piston is on the firing stroke and operate that injector and spark plug.  The engine may take a little more than two turns to start, because fuel is wasted as it condenses on the cold metal surfaces instead of exploding.  Petrol engines inject a lot of surplus fuel while cranking because of this, (the equivalent of the old fashioned choke) while diesel engines have glow plugs to heat the walls of the combustion chambers, which take a lot of energy from the battery.  The effort of the starter motor turning a cold engine with thick oil, also takes a considerable amount from the battery which then must be re-charged, using more fuel.  So, starting an engine from cold uses quite a bit of extra fuel.

 

Things are very different when re-starting a stop-start system.  The engine is warm, so no fuel condenses and no extra fuel or glow plugs are needed; the oil is thin so the engine turns over easily, the ignition has not been turned off, so the computer still “knows” the engine position and the result is the engine starts more or less instantly.  The general engineering view is that if the engine is turned off for just a few seconds, it shows a net fuel saving.

 

You raise an interesting point about how to drive these cars. You will certainly save more fuel and pollution if you wait while the traffic moves ahead of you, catch up with it, then stop again.  This may frustrate some drivers, but most realise that while the traffic is queueing they won’t gain anything by crawling along continuously.  Of course, if you are approaching a junction with a side road it is good manners to clear this as quickly as you can in case someone following wishes to turn into it, but like most things in driving, it’s a matter of observation and judgement.

 

I hope this clarifies things for you and that you can enjoy driving your stop-start car (or whatever the marketing department of that manufacturer chose to call the system) with a greater understanding of the benefits.

[fabandy]

Very interesting - thank you alianmac. I have to say, the stop-start did feel strange at first but I now find it strange to have an engine thrumming away when stopped (in another car). Now I just leave my car to it and the performance of the system has been faultless.

[Fusioncrust123]

As a long standing member of the Institue of Advanced Motorists (IAM) who has been pondering whether Stop-Start is a good thing or not since I bought my 75PS GreenTech, I thought that I would ask for their advice on this matter. Below is my query - posted on 16 April - followed by the response that I received this afternoon. Seems pretty conclusive to me. I can't think of any reason for the IAM or the AAA to big up such systems if they are not what they claim to be.

================================================================

Hi,

This email is a follow up to a response I made to a recent IAM questionnaire. In it, I said that I would appreciate advice on how to make best use of some of the more advanced technology in modern cars.

It relates to the purpose of the stop start system that is fitted to many cars under branding such as "BlueMotion", "GreenTech", "Efficient Dynamics", etc. These are the systems that automatically shut down the engine of the car when it is stationary and the driver removes their foot from the clutch pedal. They then restart the engine when the clutch pedal is depressed again.

There seems to be an assumption by the manufacturers that this happening automatically is "a good thing" and the driver should just go along with it. However, I am not so sure. I have been looking for a more in-depth analysis of these systems, what they actually achieve and what the best use of the actually is. I have not been able to find anything other than opinions expressed in discussion groups.

I wondered if you had access to any analysis or research that shows what the benefits are? Reduced fuel consumption, improvements in air quality, allowing vehicles to qualify for lower tax bands/pass stringent emissions tests are the ones that come to my mind. Also I wondered if the IAM or any other independent and responsible driving organisation had done any real world testing to see how these systems work in real life and to develop guidelines for how to use them when driving in everyday traffic. For example, when in a traffic queue that is exhibiting stop start progress, should one stop and wait, rather than crawl gradually forward? Such behaviour runs the risk of irritating drivers behind. Likewise, an observant driver can see from other traffic lights and how long the lights affecting them have been from red that they might have a very short wait (or conversely a very long wait) before they will be allowed to progress. So what is the period that the engine has to be switched off before any cost (amount of fuel or air quality) has been exceeded?

Thank you in advance for any assistance that you might be able to give me.

===========================================================

Thank you for your query.

These automatic stop-start systems are becoming almost universal for cars with piston engines, because it is relatively straightforward for manufacturers to do and it has significant advantages for both fuel economy (and thereby lower CO2 emissions) and for urban air quality. You raise some interesting questions which I’ll answer more or less in order, but first, I’m only going to deal with stop-start systems and that’s the name I’ll use. Branding such as “Blue Motion” or “Efficient dynamics” usually includes some other efficiency measures as well.

The manufacturers claim fuel saving of around 5% for typical drivers and typical journeys. The IAM does not carry out testing of this sort, but the AAA (Automobile Association of America) did conduct independent tests on three cars in 2014 and found they used 5% to 7% less fuel when the system was enabled, which corroborates the manufacturers’ claims. Urban air quality is probably an even bigger winner, because most traffic jams are in towns, where the air quality problem is worst. NOx and particulate matter (soot) from diesel engines are serious health hazards and turning the engine off when not needed means they fall to zero.

Many people have asked how long the engine has to be turned off to actually save any fuel. This is because there was a belief that it takes some extra fuel to get the engine started again, recharge the battery and so on. While this is true for a cold engine started after the car has been left overnight, it is not the case for stop-start systems.

When you switch off the ignition and leave a car, you turn off the computers controlling the engine. When you return and start the engine, it turns over at least twice before starting, because the computer needs to work out the crankshaft position before injecting fuel and firing a spark plug (on petrol engines). Only after two complete turns does it “know” which piston is on the firing stroke and operate that injector and spark plug. The engine may take a little more than two turns to start, because fuel is wasted as it condenses on the cold metal surfaces instead of exploding. Petrol engines inject a lot of surplus fuel while cranking because of this, (the equivalent of the old fashioned choke) while diesel engines have glow plugs to heat the walls of the combustion chambers, which take a lot of energy from the battery. The effort of the starter motor turning a cold engine with thick oil, also takes a considerable amount from the battery which then must be re-charged, using more fuel. So, starting an engine from cold uses quite a bit of extra fuel.

Things are very different when re-starting a stop-start system. The engine is warm, so no fuel condenses and no extra fuel or glow plugs are needed; the oil is thin so the engine turns over easily, the ignition has not been turned off, so the computer still “knows” the engine position and the result is the engine starts more or less instantly. The general engineering view is that if the engine is turned off for just a few seconds, it shows a net fuel saving.

You raise an interesting point about how to drive these cars. You will certainly save more fuel and pollution if you wait while the traffic moves ahead of you, catch up with it, then stop again. This may frustrate some drivers, but most realise that while the traffic is queueing they won’t gain anything by crawling along continuously. Of course, if you are approaching a junction with a side road it is good manners to clear this as quickly as you can in case someone following wishes to turn into it, but like most things in driving, it’s a matter of observation and judgement.

I hope this clarifies things for you and that you can enjoy driving your stop-start car (or whatever the marketing department of that manufacturer chose to call the system) with a greater understanding of the benefits.

Thanks for that, that pretty solidly answers the question i posed at the beginning of this thread. Very well explained :-)

Cheers

Martin

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[Emil]

I never thought it would be a cold start every time, but battery needs more charging after every "stop" period. Why he didn't mention anything about that.

Maybe someday I remember to read owner's manual again.

[Chris GB]

The other thing that has not been mentioned here is the fuel used (or not) replacing the battery power user for cranking and for running ancillaries while the engine is off. The smarter stop start system equipped cars have alternators that are switched to charge the battery only when you are braking, so efficiency is improve there too. The Citigo has such a system, a lot of smart tech in these little cars!