Start/Stop system - how much fuel does it use?

[ciuncky]

Just wondering if anyone has any info about how much fuel the engine requires for a quick start (ie after a Start/Stop stop session), and how does that stack against a normal idle usage per second. In my case it's a T4 AWD

The point of this? Was curious after how many seconds of keeping the engine off would i be better (consumption-wise) after it restarts?
As in many cases i stop for 3-5 seconds and then crawl forward a bit, then stop again. I can see this having a pretty bad impact on my average fuel consumption, sometimes taking off about 2mpg as opposed to just running the engine all time.

But i obviously can't be bothered to turn it off EVERY time i start the car (though i have a solution for that if i manage to find out an answer to above question, and the time required is just too long to be realistically achievable on my commute).

Any thoughts?

[hdasmith]

I don’t know how much fuel is used to start up, but the car will tell you how much fuel is being used at idle. On my D3, it says 0.1gph. You can see this using the menu button on the steering wheel, and scrolling to the bottom of the first tab.

[ciuncky]

I’ve seen that, makes sense. What does gph mean? I’d imagine not gram per hour lol?

But we’d still need the engine restart consumption

[PC40]

Gallons per hour. Vehicle is stationary so can’t be mpg.
I find keeping car moving very slowly in queues if possible rather than stopping, avoids engine cutting out and seems to improve economy. Car doesn’t default to AWD on moving away. A gentle press on the brake pedal when coming to a halt also seems to work as well. A hard press activates stop/start.

[ciuncky]

Oh, really? I thought it always had AWD engaged. I mean, when you start moving you need a lot of grip too!

I’ve noticed the gentle breaking sometimes keeps the engine running, but at other times i’m as gentle as barely keeping the car on the spot and the engine still cuts

What i noticed however is that breaking slowly for a long distance then really gentle when nearly becoming stationary does the trick in 90% of cases

Of course, the above question was more for when large traffic queues don’t really allow this or slow rolling to keep the engine on...

[PC40]

I was told and also remember reading that the AWD system (if fitted) always activates from a standstill, and then reverts to 2WD when appropriate. Traffic queues probably don’t need a lot of grip to pull away in normal circumstances. I’ve also noticed that the engine cut out sometimes seems to have a mind of its own.
AWD obviously drinks more fuel than 2WD. I know this from 19 years of owning Subaru’s.
Unfortunately I don’t know the answer to fuel use per restart, but I’m looking forward to seeing the results when you manage to get them.

[Godders]

I have never liked the stop/start system, and as far as I can see the only way of disabling it is to create an Individual driving mode. In my case I based this on the Comfort mode, the only difference being that Stop-Start is disabled. The problem though is that every time I start the car I have to remember to switch to Individual mode. I checked with Volvo and there is no way of telling the car always to start in anything other than Comfort mode, which is a pity.

[ACertainAge]

I hate the stop/start feature. The first thing I do on EVERY journey and after EVERY stop is to disable it. I have a D3R.

[sm1thy23]

I was told a couple of years ago by a friend whose a car tech that anything over 3 seconds provides a cost saving.

[Deleted User 1945]

An SAE (Society of Automotive Engineers) paper from last year quoted this for the benefit of stop start:

Euro 6d - 5-8 seconds
Euro 6 - 6-8 seconds
Euro 5 - approximately 14 seconds

For the Volvo system it will also depend upon how hard you pressed the foot break as the mechanism for releasing the break is dependant upon reaching a take off torque from the engine equivalent to the breaking force. That means the lighter you can put the break on the less fuel you will consume at take off. the harder you press the break on the more fuel you will use on take off.