Does starting up use more fuel than when idle?

[W2--]

Starter a cold engine uses a lot more fuel, but starter a hot engine uses not much more than idle.

If you sit in traffics a lot the saving is very noticeable.

 

[markjay]

Starter a cold engine uses a lot more fuel, but starter a hot engine uses not much more than idle.

If you sit in traffics a lot the saving is very noticeable.

Personally, I would find the stop/start in traffic annoying. Seen cars do this in slow traffic while walking alongside them - must be unnerving for the drivers.

While idling in traffic lights can't be a good thing, the only real solution for slow city traffic is cars equipped with electric engines, for obvious reasons - they start and stop seamlessly, and do not consume energy while stopped (well, almost - there's still lights, wipers, occupants' convenience, etc.).

Once full-electric cars become a viable proposition, I believe we will see electric cars in city centres, and fuel-burning cars doing the motorway miles and in rural areas.

 

[gIzzE]

If you took the long route but kept moving, or the short route with many traffic lights, the longer route may consume more fuel but still return superior mpg...

As a car owner, you want to save fuel, but manufacturers care more about average consumption figures than actual saving.

A good point.

I can go round the city to me parents in law and average 42mpg.
I can drive through the city and average 29mpg.

The journey through town is around 8 miles, the journey round is just a smidge over 17 miles.

 

[kit17]

I had stop/start in a loan car I had for 6 weeks, the best thing about it was not the potential fuel savings but the fact you didn't have to listen to the 4 pot diesel engine rattling away on tick over

 

[daveenty]

Originally with carburrated (is that a word?) engines, I was told that a thin film of fuel is constantly present in the venturi when the engine is running.
Once stopped, this film evaporates, thereby forming the need to recreate it when starting again, hence the using more fuel.

Modern fuel injection systems with electronic metering have all but eliminated this, therefore the stop/start system can be efficient both on fuel and, as stated above, emissions.

Disclaimer: Only going off what I was told when doing my apprenticeship *many* years ago. (didn't realise how many till I started counting back )

 

[DrNick]

In all honesty, its got to give better fuel economy to stop the engine. I see no reason that restarting an engine would use any extra fuel at all. The only extra use of energy I see is that you have to replace the power taken from the battery, thus there will be an extra load while this is replaced. The question then boils down to how long does it take to replace this energy. Looks like for a Smart its about 10 seconds.
With modern oils and manufacturing tolerences (and parts designed for stop/start) I can't see there being any appreciable extra wear and tear that would materially affect lifetime. Design it right and the lifetime should still be fine.

 

[Mr E]

About 5 weeks in now, and getting used to the stop-start on the car. Makes no difference at all to day-to-day performance, and hard to say what impact it has on fuel consumption as I haven't felt the need (other than playing with the buttons) to turn it off. Currently getting about 42.5mpg, mostly back lanes and short dual carriage way runs, as opposed to the 35mpg I got on the same mix with the W211; I don't think that there's enough stop-start in that mix to make too much of a difference.

I now only seem to notice when it doesn't turn off (i.e. when the ECO display is yellow). Come off the brakes (or touch the throttle when using hold) and the engine fires back into life, drops into gear and goes with no fuss or hesitation at all.

 

[@MARK]

In all honesty, its got to give better fuel economy to stop the engine. I see no reason that restarting an engine would use any extra fuel at all. The only extra use of energy I see is that you have to replace the power taken from the battery, thus there will be an extra load while this is replaced. The question then boils down to how long does it take to replace this energy. Looks like for a Smart its about 10 seconds.
With modern oils and manufacturing tolerences (and parts designed for stop/start) I can't see there being any appreciable extra wear and tear that would materially affect lifetime. Design it right and the lifetime should still be fine.

What about the starter motor itself.

The usage of that is going to be dramatically increased surely.

 

[markjay]

What about the starter motor itself.

The usage of that is going to be dramatically increased surely.

And battery life...

 

[markjay]

I think that the key question as far as components' service life is concerned, is whether starting the engine with zero oil pressure is not detrimental.

I appreciate the engine will be hot and there will still be lubricant film on all internal moving parts, but there will be no oil pressure for the first couple of seconds (as anyone with an older car fitted with oil pressure gauge can testify).

I don't know the answer...

 

[markjay]

Or perhaps I do... the manufacturers may have considered that a car doing many start-stop runs will never reach high mileage anyway, so the potentially shorter engine life will not be noticeable anyway.

If this is the case, then you wouldn't want to buy a second hand stop-start car that did mostly city miles during its early life and then rack-up motorway miles on it...

 

[Bellow]

What about the starter motor itself.

The usage of that is going to be dramatically increased surely.

And battery life...

Standard starter for cold start only. Combined alternator/starter motor for hot starts is the way some are going. The alternator providing some braking as per hybrid recoups the electrical energy for engine re-start.

 

[Ted]

Just to clear some things up
On my Kia ( ) which has stop/start

There is an uprated starter
There is an uprated battery with temperature sensor
There is some sort of inclinometer so that the alternator charge is less when going uphill, and more when going downhill.

It doesen't come into play when a number of conditions are present - battery voltage, battery temperature, aircon on and speed high, demist on, bonnet up, door open etc etc.

It also doesn't RE-activate until a certain distance and speed have been reached.

It works really well and unobtrusively apart from that slight feel of panic when you feel the shudder as you take your foot off the clutch in neutral.

Not sure how much fuel it saves though.

 

[markjay]

I still think it is a complex (and cumbersome) way of making an internal combustion engine do what electric engines do as standard.

 

[Bellow]

I think a battery is a cumbersome, weighty, expensive way of doing what a petrol or Diesel tank does as standard - and refills a sight quicker too!

 

[Ted]

I still think it is a complex (and cumbersome) way of making an internal combustion engine do what electric engines do as standard.


Oh, I definitely agree.
If the capacity/weight/cost issues with batteries were overcome, I'm sure I would be in the queue.

Maximimum torque at 0 RPM - I'm up for that!

 

[markjay]

I think a battery is a cumbersome, weighty, expensive way of doing what a petrol or Diesel tank does as standard - and refills a sight quicker too!

Oh, I definitely agree.
If the capacity/weight/cost issues with batteries were overcome, I'm sure I would be in the queue.

Maximimum torque at 0 RPM - I'm up for that!

I agree... and hence my previous comment. There is no one ideal solution for all situations. Electric cars for cities, internal combustion for motorways and rural areas.