Eco option on XF

[Norfolk Ian]

So today I took my XF out for its first run, I found it had an Eco button - I’d appreciate your thoughts and advice on its use. I took my XF to my childhood home (house in background of photo) for its first drive.

[LairdScooby]

Is the Eco button on the Climate Control (heater) panel Ian? If so, it will almost certainly switch the AC compressor off but normal operation will let the AC compressor run as and when necessary.

If it's with the gear selector, i would guess it's an economy mode for the gearbox.

[Raistlin]

Your car defaults to engine stop / start during short stops Ian. Pressing the button disables the function until you recycle ignition (or press it again).

[Norfolk Ian]

Thank you both, do either of you think is has any benefits using it or if it causes and problems 🙏

[Raistlin]

I hate it with a passion.

[LairdScooby]

Thankfully i don't have it on mine (hence my ignorance about the button) but my friend has it on her Audi - complete and utter pain in the rear!

If it was me, i'd turn it off as well, puts undue strain on the starter and no doubt the battery too (although cars with Start-Stop have beefier batteries to cope, allegedly) not to mention taking the decision making from me.

I'm a big boy now, i know when to switch the engine off due to long delays due to roadworks, heavy traffic etc.

[Big John]

On 10/24/2023 at 12:42 PM, Norfolk Ian said:

Thank you both, do either of you think is has any benefits using it or if it causes and problems 🙏

Hi Ian

Stop/Start is quite a marmite function. Most  people love it or hate it. Potential negatives are usually related to engine and/or starter wear and tear. Most engine and starter pinion wear is at start up, however stop/start actually pre-engages the starter pinion so not really an issue. The middle position is people not liking not being in control or insecurity that engine will start again 🙂

Positives are that it does reduce emissions (the actual rationale for its introduction). If it engages you know your battery/batteries are OK as it will not engage if it is not sure it can restart the car.

Personally I let it engage at least once each journey before disabling as this confirms batteries are OK.
If going anywhere when car is to be left for a few days I would always disable as the XF does conduct occasional self tests of the battery which involves discharging to 75% capacity. My concern is always that id gets to that point just before I park up so instead of starting with 100% I would be starting with 75% 😞

As you may know the XF along with many modern cars does seem to suffer from parasitic drain so I only leave mine for a week at most before attaching my ctek.

J

[Norfolk Ian]

Thank you John I appreciate the advice, I’m loving my XF 

[LairdScooby]

6 hours ago, Big John said:

however stop/start actually pre-engages the starter pinion so not really an issue.

Errr, i beg to differ - pre-engaged starters have been around for donkeys years and holding the pinion in so it was "ready" to restart would cause a considerable battery drain (~30A usually for hold-in current) which would flatten the battery fairly quickly.

Also because of how the starter solenoid operates, it pulls the pinon into engagement and then makes the circuit but there are no half-measures - it pulls in and then the contacts are automatically closed so the motor operates.

[Big John]

8 hours ago, LairdScooby said:

Errr, i beg to differ - pre-engaged starters have been around for donkeys years and holding the pinion in so it was "ready" to restart would cause a considerable battery drain (~30A usually for hold-in current) which would flatten the battery fairly quickly.

Also because of how the starter solenoid operates, it pulls the pinon into engagement and then makes the circuit but there are no half-measures - it pulls in and then the contacts are automatically closed so the motor operates.

Hi Dave

In answer to your first point I agree, that is what I said 🙂 , I woould never use it if my destination was an Airport car park! However proponents would argue that is why the cars use AGM batteries that are designed for repeated deep discharge (I don't see myself approaching the expected service specification of over 300000 starts in the next five years).

On the second point, again I sort of agree. However, as I said on wear and tear, this is accounted for by the design to minimse wear. A nice little article here: https://haynes.com/en-gb/tips-tutorials/stop-start-technology-explained

As I said it is a marmite issue 🙂

J

[LairdScooby]

3 hours ago, Big John said:

On the second point, again I sort of agree. However, as I said on wear and tear, this is accounted for by the design to minimse wear. A nice little article here: https://haynes.com/en-gb/tips-tutorials/stop-start-technology-explained

From the article John :

If you've ever tried to start a car that's already running you'll have discovered that it makes a hideous crunching sound as the starter pinion tries to engage with a rapidly spinning flywheel!

As a result single solenoid Stop-Start systems can pause the starting process and prevent the engine from starting until it's fully stopped – this isn't ideal as the car doesn't start 'on demand' but a moment later.

A tandem solenoid works by spinning up the starter pinion to synchronise it with the flywheel, then the second solenoid seamlessly engages the gear.

Highlighted and underlined the relevant bit - surely a contradiction in terms? The idea is to prevent the graunching of the starter pinion on a turning flywheel/ring gear so by spinning a starter pinion up and engaging with a ring gear (moving or not) the effect would be the same as trying to engage a stationary pinion with a spinning ring gear.

Maybe it's just that haynes haven't explained it all that well but either way, a solenoid has a hefty current draw and i'm struggling to reconcile the concept of an excessive current draw with the need to start 50uS quicker than the conventional arrangement. More research is needed i think!

 

*** EDIT ***

Having done a bit more digging, it appears that is exactly how the sytem works. I'm much more used to starters that turn the engine at 250-300rpm to start them, it seems the newer motors are capable of spinning much faster to enable meshing with the ring gear at the same speed but it must be a very critical line of getting the two speeds matched! 😮

Also discovered the Permanently Engaged starter which presumably has a starter clutch inside to connect the starter pinion to the motor.

Definitely Marmite!

[Norfolk Ian]

Hi Dave & John,

Thanks for your advice and knowledge. I’m not mechanical at all, so having a source of knowledge in the club is really helpful.

🙏 Ian